Ivermectin-facilitated immunity in onchocerciasis; activation of parasite-specific Th1-type responses with subclinical Onchocerca volvulus infection

Association of haemato-biochemical indices and blood composite ratios with microfilaridermia in Onchocerciasis patients

BACKGROUND

Onchocerciasis causes chronic systemic inflammation. Several studies have used markers such as haemato-biochemical indices to predict the occurrence of systemic inflammation. This study assessed the variability and predictability of haemato-biochemical indices and blood composite ratios (BCRs) in microfilariae positive (MF+) and microfilariae negative (MF-) subgroups of onchocercomata participants.

METHODS

One hundred and five (105) MF + and 34 MF- participants were retrospectively recruited into the study. Screening for the presence of O. volvulus microfilariae was done from skin snips taken from the left and right iliac crests of participants using established and approved protocols. Haematological and biochemical indices were measured using standard laboratory automated analyzers. Blood composite ratios (BCRs) were calculated as ratios of the absolute parameters involved.

RESULTS

A significantly increased total WBC, absolute eosinophil, eosinophil percent and absolute basophil were observed in the MF + participants compared to MF- participants. Reduced gamma-glutamyl transferase (GGT) with increased estimated glomerular filtration rate (eGFR) was significantly associated with MF + participants compared to MF- participants. BCRs were significantly higher for eosinophil-to-neutrophil ratio (ENR), eosinophil-to-monocyte ratio (EMR), eosinophil-to-basophil ratio (EBR) and eosinophil-to-lymphocyte ratio (ELR) in MF + participants compared to MF- participants. After multivariate adjustment, onchocercomata participants with increased eosinophil counts (aOR = 13.86, 95% CI [2.07-92.90], p = 0.007), ENR x10 (aOR = 1.42, 95% CI [1.05-1.93], p = 0.025), EMR (aOR = 2.64, 95% CI [1.25-5.60], p = 0.011), EBR (aOR = 1.07, 95% CI [1.01-1.10], p = 0.020) and ELR x10 (aOR = 1.69, 95% CI [1.14-2.51], p = 0.009) were more likely to have microfilaridermia.

CONCLUSIONS

Elevated eosinophil counts with higher ENR, EMR, EBR and ELR levels are significantly associated with microfilaridermia in onchocercomata participants. Combining BCRs with eosinophil count significantly led to an improvement in the conventional model for predicting microfilaridermia.

Development of a recombinant vaccine against human onchocerciasis

INTRODUCTION

Human onchocerciasis caused by the filarial nematode parasite Onchocerca volvulus remains a major cause of debilitating disease infecting millions primarily in Sub-Saharan Africa. The development of a prophylactic vaccine, along with mass drug administration, would facilitate meeting the goal of onchocerciasis elimination by 2030.

AREAS COVERED

Models used to study immunity to Onchocerca include natural infection of cattle with Onchocerca ochengi and O. volvulus infective third-stage larvae implanted within diffusion chambers in mice. A vaccine, comprised of two adjuvanted recombinant antigens, induced protective immunity in genetically diverse mice suggesting that it will function similarly in diverse human populations. These antigens were recognized by immune humans and also induced protective immunity against Brugia malayi. We describe the development of a fusion protein composed of the two vaccine antigens with the plan to test the vaccine in cows and non-human primates as a prelude to the initiation of phase 1 clinical trials.

EXPERT OPINION

The adjuvanted O. volvulus vaccine composed of two antigens Ov-103 and Ov-RAL-2 was shown to be consistently effective at inducing protective immunity using multiple immune mechanisms. The vaccine is ready for further evaluation in other animal models before moving to clinical trials in humans.

Computational Design and Preliminary Serological Analysis of a Novel Multi-Epitope Vaccine Candidate against Onchocerciasis and Related Filarial Diseases

: Onchocerciasis is a skin and eye disease that exerts a heavy socio-economic burden, particularly in sub-Saharan Africa, a region which harbours greater than 96% of either infected or at-risk populations. The elimination plan for the disease is currently challenged by many factors including amongst others; the potential emergence of resistance to the main chemotherapeutic agent, ivermectin (IVM). Novel tools, including preventative and therapeutic vaccines, could provide additional impetus to the disease elimination tool portfolio. Several observations in both humans and animals have provided evidence for the development of both natural and artificial acquired immunity. In this study, immuno-informatics tools were applied to design a filarial-conserved multi-epitope subunit vaccine candidate, (designated Ov-DKR-2) consisting of B-and T-lymphocyte epitopes of eight immunogenic antigens previously assessed in pre-clinical studies. The high-percentage conservation of the selected proteins and epitopes predicted in related nematode parasitic species hints that the generated chimera may be instrumental for cross-protection. Bioinformatics analyses were employed for the prediction, refinement, and validation of the 3D structure of the Ov-DKR-2 chimera. In-silico immune simulation projected significantly high levels of IgG1, T-helper, T-cytotoxic cells, INF-γ, and IL-2 responses. Preliminary immunological analyses revealed that the multi-epitope vaccine candidate reacted with antibodies in sera from both onchocerciasis-infected individuals, endemic normals as well as loiasis-infected persons but not with the control sera from European individuals. These results support the premise for further characterisation of the engineered protein as a vaccine candidate for onchocerciasis.

Nitazoxanide/azithromycin combination for COVID-19: A suggested new protocol for early management

Azithromycin has been shown to have a clinical efficacy against severe acute respiratory syndrome coronavirus 2; ivermectin has also demonstrated a remarkable experimental efficacy with a potential to be used for Coronavirus disease 2019. Further, BCG vaccination is being considered for clinical trials aiming to test its potential for lowering COVID-19 morbidity and mortality. This article illustrates some structural and functional relationships that may gather these drugs and the author, basing on a combined pathophysiological and pharmacological approach, recommends the FDA-approved antidiarrhea drug; nitazoxanide, which has been previously suggested but unfortunately widely ignored, to be tested in combination with azithromycin for their potential activity against SARS CoV-2, soonest. The author also recommends testing their combined administration as early during the clinical course of COVID-19 as possible. Further, basing on the same represented concept, the author suggests more trials for interferons to be tested against SARS CoV-2, especially in severe and critical COVID-19 cases.

Modelling exposure heterogeneity and density dependence in onchocerciasis using a novel individual-based transmission model, EPIONCHO-IBM: Implications for elimination and data needs

BACKGROUND

Density dependence in helminth establishment and heterogeneity in exposure to infection are known to drive resilience to interventions based on mass drug administration (MDA). However, the interaction between these processes is poorly understood. We developed a novel individual-based model for onchocerciasis transmission, EPIONCHO-IBM, which accounts for both processes. We fit the model to pre-intervention epidemiological data and explore parasite dynamics during MDA with ivermectin.

METHODOLOGY/PRINCIPAL FINDINGS

Density dependence and heterogeneity in exposure to blackfly (vector) bites were estimated by fitting the model to matched pre-intervention microfilarial prevalence, microfilarial intensity and vector biting rate data from savannah areas of Cameroon and Côte d'Ivoire/Burkina Faso using Latin hypercube sampling. Transmission dynamics during 25 years of annual and biannual ivermectin MDA were investigated. Density dependence in parasite establishment within humans was estimated for different levels of (fixed) exposure heterogeneity to understand how parametric uncertainty may influence treatment dynamics. Stronger overdispersion in exposure to blackfly bites results in the estimation of stronger density-dependent parasite establishment within humans, consequently increasing resilience to MDA. For all levels of exposure heterogeneity tested, the model predicts a departure from the functional forms for density dependence assumed in the deterministic version of the model.

CONCLUSIONS/SIGNIFICANCE

This is the first, stochastic model of onchocerciasis, that accounts for and estimates density-dependent parasite establishment in humans alongside exposure heterogeneity. Capturing the interaction between these processes is fundamental to our understanding of resilience to MDA interventions. Given that uncertainty in these processes results in very different treatment dynamics, collecting data on exposure heterogeneity would be essential for improving model predictions during MDA. We discuss possible ways in which such data may be collected as well as the importance of better understanding the effects of immunological responses on establishing parasites prior to and during ivermectin treatment.

In-silico design of a multi-epitope vaccine candidate against onchocerciasis and related filarial diseases

Onchocerciasis is a parasitic disease with high socio-economic burden particularly in sub-Saharan Africa. The elimination plan for this disease has faced numerous challenges. A multi-epitope prophylactic/therapeutic vaccine targeting the infective L3 and microfilaria stages of the parasite's life cycle would be invaluable to achieve the current elimination goal. There are several observations that make the possibility of developing a vaccine against this disease likely. For example, despite being exposed to high transmission rates of infection, 1 to 5% of people have no clinical manifestations of the disease and are thus considered as putatively immune individuals. An immuno-informatics approach was applied to design a filarial multi-epitope subunit vaccine peptide consisting of linear B-cell and T-cell epitopes of proteins reported to be potential novel vaccine candidates. Conservation of the selected proteins and predicted epitopes in other parasitic nematode species suggests that the generated chimera could be helpful for cross-protection. The 3D structure was predicted, refined, and validated using bioinformatics tools. Protein-protein docking of the chimeric vaccine peptide with the TLR4 protein predicted efficient binding. Immune simulation predicted significantly high levels of IgG₁, T-helper, T-cytotoxic cells, INF-γ, and IL-2. Overall, the constructed recombinant putative peptide demonstrated antigenicity superior to current vaccine candidates.

Prediction and validation of the structural features of Ov58GPCR, an immunogenic determinant of Onchocerca volvulus

Onchocerciasis is a severely debilitating yet neglected tropical disease (NTD) that creates social stigma, generates and perpetuates poverty, and leads ultimately in some cases to irreversible unilateral or bilateral blindness if untreated. Consequently, the disease is a major impediment to socioeconomic development. Many control programs have been launched for the disease with moderate successes achieved. This mitigated hit is partially due to the lingering need for reliable, non-invasive and easily applicable tools for mapping endemic regions and post-elimination surveillance. In this work, bioinformatics analyses combined with immunological assays were applied in a bid to develop potential tools for diagnosis and assessing the success of drug treatment programs. We report that (i) the O. volvulus antigen, Ov58GPCR is a G-protein coupled receptor (GPCR) conserved in related nematodes, (ii) synthetic peptides predicted to be in the extracellular domain (ECD) of Ov58GPCR are indeed immunogenic epitopes in actively-infected individuals, (iii) synthetic peptide cocktails discriminate between actively-infected individuals, treated individuals and healthy African controls, (iv) polyclonal antibodies against one of the peptides or against the bacterially-expressed ECD reacted specifically with the native antigen of O. volvulus total and surface extracts, (v) Ov58GPCR is transcribed in both larvae and adult parasite stages, (vi) IgG and IgE responses to the recombinant ECD decline with ivermectin treatment. All these findings suggest that the extracellular domain and synthetic peptides of Ov58GPCR, as well as the specific immune response generated could be harnessed in the context of disease diagnosis and surveillance.

Examining the role of macrolides and host immunity in combatting filarial parasites

Macrocyclic lactones (MLs), specifically the avermectins and milbemycins, are known for their effectiveness against a broad spectrum of disease-causing nematodes and arthropods in humans and animals. In most nematodes, drugs in this class induce paralysis, resulting in starvation, impaired ability to remain associated with their anatomical environment, and death of all life stages. Initially, this was also thought to be the ML mode of action against filarial nematodes, but researchers have not been able to validate these characteristic effects of immobilization/starvation of MLs in vitro, even at higher doses than are possible in vivo. Relatively recently, ML receptor sites exclusively located proximate to the excretory-secretory (ES) apparatus were identified in Brugia malayi microfilaria and an ML-induced suppression of secretory protein release by B. malayi microfilariae was demonstrated in vitro. It is hypothesized here that suppression of these ES proteins prevents the filarial worm from interfering with the host's complement cascade, reducing the ability of the parasite to evade the immune system. Live microfilariae and/or larvae, thus exposed, are attacked and presented to the host's innate immune mechanisms and are ultimately killed by the immune response, not the ML drug. These live, exposed filarial worms stimulate development of innate, cellular and humoral immune responses that when properly stimulated, are capable of clearing all larvae or microfilariae present in the host, regardless of their individual sensitivity to MLs. Additional research in this area can be expected to improve our understanding of the relationships among filarial worms, MLs, and the host immune system, which likely would have implications in filarial disease management in humans and animals.

Distinctive cytokine, chemokine, and antibody responses in Echinococcus multilocularis-infected patients with cured, stable, or progressive disease

Metacestode larvae of the tapeworm Echinococcus multilocularis can cause alveolar echinococcosis (AE), a severe parasitic disease in man, which, if it remains untreated, may cause organ failure and death. Spontaneous and parasite antigen-induced cellular responses were studied in patients with cured, stable, and progressive AE to differentiate the response profiles between the distinct states of infection. Antibody reactivity was evaluated in AE patients with cured, stable, and progressive disease. The spontaneous cellular release of pro-inflammatory IL-31 and IL-33 was clearly depressed in all AE patients, while regulatory IL-27, anti-inflammatory SDF-1/CXCL12, and eosinophil granulocyte attracting Eotaxin-1, Eotaxin-2, and Eotaxin-3 (CCL11, CCL24, CCL26) were enhanced with disease progression. Such distinctive response profiles could be applied for monitoring of AE disease progression or regression. E. multilocularis metacestode (Em) antigens (entire metacestode EmAg as well as EmVesicles) stimulated in vitro IL-31, IL-33, Eotaxin-1, Eotaxin-3, and CXCL12 cytokine and chemokine responses, which were similarly present in all AE patient groups, while regulatory IL-27 was suppressed and pro-inflammatory Eotaxin-2 was enhanced. E. multilocularis metacestode-specific IgG1, IgG3, and IgE responses progressively diminished with regression from active to stable and cured AE. IgG2 and IgG4 reactivity remained similarly high in stable and progressive cases, and lessened only with cured AE. Antibody reactivity against E. multilocularis vesicle antigen distinctively separated between cured, stable, or progressive AE, with the exception of IgG4. In sum, the combined and longitudinal study of several cytokines and chemokines, together with the evaluation of E. multilocularis vesicle-specific antibody responses, should provide a better understanding of the immune response during progression and regression of AE, and may help to improve the staging of AE patients.

Density-dependent mortality of the human host in onchocerciasis: relationships between microfilarial load and excess mortality

Background

The parasite Onchocerca volvulus has, until recently, been regarded as the cause of a chronic yet non-fatal condition. Recent analyses, however, have indicated that in addition to blindness, the parasite can also be directly associated with human mortality. Such analyses also suggested that the relationship between microfilarial load and excess mortality might be non-linear. Determining the functional form of such relationship would contribute to quantify the population impact of mass microfilaricidal treatment.

Methodology/Principal Findings

Data from the Onchocerciasis Control Programme in West Africa (OCP) collected from 1974 through 2001 were used to determine functional relationships between microfilarial load and excess mortality of the human host. The goodness-of-fit of three candidate functional forms (a (log-) linear model and two saturating functions) were explored and a saturating (log-) sigmoid function was deemed to be statistically the best fit. The excess mortality associated with microfilarial load was also found to be greater in younger hosts. The attributable mortality risk due to onchocerciasis was estimated to be 5.9%.

Conclusions/Significance

Incorporation of this non-linear functional relationship between microfilarial load and excess mortality into mathematical models for the transmission and control of onchocerciasis will have important implications for our understanding of the population biology of O. volvulus, its impact on human populations, the global burden of disease due to onchocerciasis, and the projected benefits of control programmes in both human and economic terms.

Human onchocerciasis (River Blindness) is a parasitic disease leading to visual impairment including blindness. Blindness may lead to premature death, but infection with the parasite itself (Onchocerca volvulus) may also cause excess mortality in sighted individuals. The excess risk of mortality may not be directly (linearly) proportional to the intensity of infection (a measure of how many parasites an individual harbours). We analyze cohort data from the Onchocerciasis Control Programme in West Africa, collected between 1974 and 2001, by fitting a suite of quantitative models (including a ‘null’ model of no relationship between infection intensity and mortality, a (log-) linear function, and two plateauing curves), and choosing the one that is the most statistically adequate. The risk of human mortality initially increases with parasite density but saturates at high densities (following an S-shape curve), and such risk is greater in younger individuals for a given infection intensity. Our results have important repercussions for programmes aiming to control onchocerciasis (in terms of how the benefits of the programme are calculated), for measuring the burden of disease and mortality caused by the infection, and for a better understanding of the processes that govern the density of parasite populations among human hosts.

Chemokines and cytokines in patients with an occult Onchocerca volvulus infection

Repeated ivermectin treatment will clear microfilaria (Mf) of Onchocerca volvulus from skin and eyes of onchocerciasis patients while adult filaria remains alive and reproductive, and such occult O. volvulus infection may persist for years. To investigate the effect of residual adult filaria on the immune response profile, chemokines and cytokines were quantified 1) in onchocerciasis patients who developed an occult O. volvulus infection (Mf-negative) due to repeated ivermectin treatments, 2) patients who became Mf-negative without ivermectin treatments due to missing re-infection, and 3) endemic and non-endemic O. volvulus Mf-negative controls. With occult O. volvulus infection, serum levels of pro-inflammatory chemokines MCP-1/CCL2, MIP-1α/CCL3, MIP-1β/CCL4, MPIF-1/CCL23 and CXCL8/IL-8 enhanced and approached higher concentrations as determined in infection-free controls, whilst regulatory and Th2-type cytokines and chemokines MCP-4/CCL13, MIP-1δ/CCL15, TARC/CCL17 and IL-13 lessened. Levels of Eotaxin-2/CCL24, MCP-3/CCL7 and BCA-1/CXCL13 remained unchanged. At 3 days post-initial ivermectin treatment, MCP-1/CCL2, MCP-4/CCL13, MPIF-1/CCL23 and Eotaxin-2/CCL24 were strongly enhanced, suggesting that monocytes and eosinophil granulocytes have mediated Mf clearance. In summary, with occult and expiring O. volvulus infections the serum levels of inflammatory chemokines enhanced over time while regulatory and Th2-type-promoting cytokines and chemokines lessened; these changes may reflect a decreasing effector cell activation against Mf of O. volvulus, and in parallel, an enhancing inflammatory immune responsiveness.

Control of onchocerciasis in Africa: threshold shifts, breakpoints and rules for elimination

Control of onchocerciasis in Africa is currently based on annual community-directed treatment with ivermectin (CDTI) which has been assumed to be not efficient enough to bring about elimination. However, elimination has recently been reported to have been achieved by CDTI alone in villages of Senegal and Mali, reviving debate on the eradicability of onchocerciasis in Africa. We investigate the eradicability of onchocerciasis by examining threshold shifts and breakpoints predicted by a stochastic transmission model that has been fitted extensively to data. We show that elimination based on CDTI relies on shifting the threshold biting rate to a level that is higher than the annual biting rate. Breakpoints become relevant in the context of when to stop CDTI. In order for the model to predict a good chance for CDTI to eliminate onchocerciasis, facilitating factors such as the macrofilaricidal effect of ivermectin must be assumed. A chart predicting the minimum efficacy of CDTI required for elimination, dependent on the annual biting rate, is provided. Generalisable recommendations into strategies for the elimination of onchocerciasis are derived, particularly referring to the roles of vectors, the residual infection rate under control, and a low-spreader problem originating from patients with low parasite burdens.

Identifying sub-optimal responses to ivermectin in the treatment of River Blindness

Identification of drug resistance before it becomes a public health concern requires a clear distinction between what constitutes a normal and a suboptimal treatment response. A novel method of analyzing drug efficacy studies in human helminthiases is proposed and used to investigate recent claims of atypical responses to ivermectin in the treatment of River Blindness. The variability in the rate at which Onchocerca volvulus microfilariae repopulate host's skin following ivermectin treatment is quantified using an individual-based onchocerciasis mathematical model. The model estimates a single skin repopulation rate for every host sampled, allowing reports of suboptimal responses to be statistically compared with responses from populations with no prior exposure to ivermectin. Statistically faster rates of skin repopulation were observed in 3 Ghanaian villages (treated 12-17 times), despite the wide variability in repopulation rates observed in ivermectin-naïve populations. Another village previously thought to have high rates of skin repopulation was shown to be indistinguishable from the normal treatment response. The model is used to generate testable hypotheses to identify whether atypical rates of skin repopulation by microfilariae could result from low treatment coverage alone or provide evidence of decreased ivermectin efficacy. Further work linking phenotypic poor responses to treatment with parasite molecular genetics markers will be required to confirm drug resistance. Limitations of the skin-snipping method for estimating parasite load indicates that changes in the distribution of microfilarial repopulation rates, rather than their absolute values, maybe a more sensitive indicator of emerging ivermectin resistance.

Onchocerca volvulus-specific antibody and cytokine responses in onchocerciasis patients after 16 years of repeated ivermectin therapy

The recommended control option against onchocerciasis is repeated ivermectin treatment, which will need to be implemented for decades, and it remains unknown how repeated ivermectin therapy might affect immunity against Onchocerca volvulus in the long term. O. volvulus-specific antibody reactivity and cellular cytokine production were investigated in onchocerciasis patients receiving ivermectin (150 microg/kg) annually for 16 years. In treated patients, the T helper type 2 (Th2) cytokine interleukin (IL)-5 and T regulatory IL-10 in response to O. volvulus antigen (OvAg) and bacteria-derived Streptolysin O (SL-O) diminished to levels found in infection-free endemic controls; also, cellular release of Th1-type interferon (IFN)-gamma at 16 years post initial ivermectin treatment (p.i.t.) approached control levels. In ivermectin-treated onchocerciasis patients, IL-5 production in responses to the mitogen phytohaemagglutinin (PHA) decreased, but IL-10 in response PHA increased, and neither attained the cytokine production levels of endemic controls. At 16 years p.i.t., O. volvulus-specific IgG1 and IgG4 subclass reactivity still persisted at higher levels in onchocerciasis patients than in O. volvulus exposed but microfilariae-free endemic controls. In addition, cytokine responses remained depressed in onchocerciasis patients infected concurrently with Mansonella perstans and Necator americanus or Entamoeba histolytica/dispar. Thus, long-term ivermectin therapy of onchocerciasis may not suffice to re-establish fully a balanced Th1 and Th2 immune responsiveness in O. volvulus microfilariae-negative individuals. Such deficient reconstitution of immune competence may be due to an as yet continuing and uncontrolled reinfection with O. volvulus, but parasite co-infections can also bias and may prevent the development of such immunity.

Cytokine and chemokine responses in patients co-infected with Entamoeba histolytica/dispar, Necator americanus and Mansonella perstans and changes after anti-parasite treatment

This study examined the impact of concurrent parasite infections (amoebiasis, filariasis, necatoriasis) and the effect of anti-parasite treatment on cytokine and chemokine responses in singly and poly-parasitized patients. Cellular reactivity and parasite-specific Th1- and Th2-type cytokine and chemokine profiles were investigated before and six weeks after treatment. In those patients infected with three parasite species, cellular secretion of interleukin 5 (IL-5) and IL-12p40 by PBMC was strongly diminished (p<0.005) but IL-10 was elevated in parasite-infected patients (p<0.0001) in response to protozoa- and helminth-specific as well as bacteria-specific antigens. Macrophage inflammatory chemokines (MIP-1alpha/CCL3 and MIP-1beta/CCL4), macrophage-derived chemokine (MDC/CCL22) and neutrophil activating chemokine (IL-8/CXCL8) were produced by PBMC in similar amounts in endemic controls and singly and poly-parasitized patients, but thymus and activation-regulated chemokine (TARC/CCL17) was produced the highest by PBMC from patients with triple parasite infections (p<0.0001). Following anti-parasite therapy, secretion of IL-12p40 and IL-5 augmented significantly in treated patients while IL-10, MDC, MIP-1alpha, TARC and IL-8 substantially diminished (all p<10(-5)) when their PBMC were activated with parasite- and bacteria-specific antigens. In summary, PBMC from poly-parasitized patients responded to protozoa- and helminth-specific antigens with a compromised IL-5 and IL-12p40 but high IL-10 and a substantial chemokine release. Chemokines may attract and activate effector cells in peri-parasitic tissues to limit parasite proliferation and dissemination, while depressed IL-5 and IL-12p40 but prominent IL-10 may prevent eosinophil and cytotoxic cell-mediated inflammatory processes and pathogenesis to the host. The changes in this profile following anti-parasite therapy disclosed the dynamics of an immune adaptation associated with parasite accumulation and also with clearance of parasite infections.

Chemokines in onchocerciasis patients after a single dose of ivermectin

Ivermectin treatment will effectively diminish microfilariae (Mf) of Onchocerca volvulus in the skin of patients, but therapy is associated with adverse host inflammatory responses. To investigate the association of proinflammatory chemokines with the intensity of infection and clinical adverse reactions, chemokine serum levels were measured in patients following ivermectin treatment (100 microg/kg, 150 microg/kg or 200 microg/kg) or placebo. The density of O. volvulus Mf per mg skin decreased by 85%, 97%, 97% and 90% at day 3, at month 3, month 6 and at 1 year post-ivermectin. The cutaneous T cell-attracting chemokine (CTACK/CCL27) was found highly elevated in onchocerciasis patients compared to infection-free European controls (P = 0.0004) and it did not change following ivermectin or placebo to 1 year post-therapy. The chemokine RANTES/CCL5 (regulated on activated and normally T cell-expressed) was similarly high in onchocerciasis patients and infection-free European controls; the RANTES/CCL5 levels did not change following treatment until 6 months post-therapy but were slightly elevated at 1 year post-therapy (P < 0.02). In contrast, the Th2-type chemoattractants, thymus and activation regulated chemokine (TARC/CCL17) and macrophage-derived chemokine (MDC/CCL22), were activated at 3 days post-ivermectin (P < 0.0001) to return to pretreatment or lower levels thereafter. The Th1-type chemoattractants, macrophage inflammatory protein (MIP)-1alpha/CCL3 and MIP-1beta/CCL4 were low before ivermectin treatment, but following clearance of microfilariae of O. volvulus their levels increased from 6 months post-therapy onwards (for both at 12 months post-therapy, P < 0.0001). The adverse reaction scores (RS) in treated patients increased significantly on day 3 (P < 0.02) while it remained unchanged in those who received placebo (P = 0.22); RS interacted with the microfilarial density (P = 0.01), but not with the dose of ivermectin or with the serum levels of MIP-1alpha/CCL3, MIP-1beta/CCL4, TARC/CCL17, MDC/CCL22 and CTACK/CCL27. Our observations suggest that following ivermectin, macrophages as well as memory Th2-type lymphocytes and B cells, attracted and activated by MDC/CCL22, TARC/CCL17 and CTACK/CCL27, may contribute to dermal immune responses and O. volvulus Mf killing and clearance. The transient changes of TARC/CCL17 and MDC/CCL22 were not associated with clinical adverse responses, and the later rise of MIP-1alpha/CCL3 and MIP-1beta/CCL4 showed a reactivation of Type 1 immune responses associated with persistent low levels of O. volvulus microfilariae and an expiring O. volvulus infection.

Immunomodulatory effect of various anti-parasitics: a review

This paper reviews the immunomodulatory effects (immunosuppression or immunoactivation) of various anthelmintics including levamisole, fenvalerate, dieldrin, carbofuran, aminocarb, thiabendazole, fenbendazole, oxfendazole and ivermectin. The induced modulation of immune function may occur via direct and/or indirect mechanisms. The immunomodulatory effects of these anti-parasitics have been studied in a variety of bacterial (e.g. brucellosis, salmonellosis, paratuberculosis, mastitis), viral (e.g. infectious bovine rhinotracheitis, Herpes, foot and mouth disease), parasitic (e.g. onchocerciasis, coccidiosis, ascariasis, schistosomiasis) and neoplastic diseases. Some antiparasitics have also been used to boost immunity in a number of human diseases including leprosy, Hodgkin's disease, rheumatoid arthritis, and in adjuvanted therapy of colorectal cancer. The ability to stimulate the immune response of animals offers a new means of disease intervention. Future research on immunomodulatory effects of anti-parasitics, for humans and domestic farm animals, will provide additional methods of treating immunosuppressed subjects. The immunopotentiating or immunosuppressing activity of anti-parasitics will dictate whether co-administration of vaccines and anthelmintics or administration of vaccines during the window of immunoactivation is justified or not.

Cattle protected from onchocerciasis by ivermectin are highly susceptible to infection after drug withdrawal

Ivermectin administration is now the major tool in the control of human onchocerciasis (caused by Onchocerca volvulus) based on its suppression of microfilariae and hence the prevention of disease. However, in Africa, transmission is not eliminated and treated populations continue to be exposed to infective larval (L(3)) challenge, albeit at reduced levels. We have investigated whether protective immunity might develop under such conditions using the analogous host-parasite system Onchocerca ochengi in cattle, based on our previous findings in cattle exposed to challenge, that in vivo ivermectin attenuates the development of adult infections and that irradiation-attenuated L(3) induce significant protection. In a two-phase prospective study over 4 years, groups of cattle were exposed to severe natural challenge. In the first phase, 38/40 animals treated either with ivermectin or with moxidectin at either monthly or 3-monthly intervals had not developed detectable infections after 22 months of exposure whereas, in a non-treated control group (n = 14) nodule prevalence was 78.6% and the geometric mean (range) nodule load was 4.8 (0-33). In the second phase, all drug treatments were withdrawn, a new control group (n = 8) introduced, and exposure continued at the same site. After 24 months, all groups had developed patent infections, with geometric mean (range) nodule loads of 17.4 (4-99), 38.4 (10-111), 50.7 (26-86), 14.3 (0-69) and 14.7 (0-55) for the control, monthly-ivermectin, 3-monthly ivermectin, monthly moxidectin and 3-monthly moxidectin groups, respectively. There was no evidence of protection-indeed the 3-monthly ivermectin group was significantly (P < 0.05) hyper-susceptible. In addition, microfilarial densities and the rate of increase in microfilarial load were significantly higher (P < 0.05) in the ivermectin-treated groups than in control animals. These results have important implications for ivermectin-based control of human onchocerciasis and suggest that humans exposed to ongoing transmission in endemic areas whilst receiving ivermectin are unlikely to develop immunity and will be highly susceptible should drug distribution cease.

Regulatory effects of IL-12 and IL-18 on Onchocerca volvulus- and Entamoeba histolytica-specific cellular reactivity and cytokine profiles

In the present study, the cytokines interleukin (IL)-12 and IL-18 were evaluated for their capacity to modulate and to re-direct in vitro parasite antigen-specific cellular responsiveness in patients exposed to Onchocerca volvulus and Entamoeba histolytica infection. We found that IL-18 was highly capable of reducing parasite antigen-induced IL-10 production by PBMC. In contrast, addition or neutralization of IL-12, also in combination with IL-18 and the interferon-gamma-inducible chemokine IP-10 did not affect IL-10 production. Interestingly, the highest IL-10 levels were measured when IL-18 and IP-10 were both neutralized. Although having no effect on IL-10, IL-12 strongly promoted spontaneous and parasite antigen-driven IFN-gamma production by PBMC, whereas IL-18 was only moderately affecting IFN-gamma release by PBMC re-stimulated with E. histolytica- or O. volvulus-specific antigens. Both IL-12 and IL-18 diminished the cellular production of IL-13, and a synergistic effect was observed when the cytokines were combined. Likewise, neutralization of IL-12 enhanced Entamoeba and Onchocerca antigen-driven IL-13 production, but no further increase of IL-13 was observed, when anti-IL-12 and anti-IL-18 were used together. This study disclosed that IL-18 will significantly down-regulate parasite-specific IL-10 production, whereas IL-12 induced IFN-gamma and inhibited IL-13 production by PBMC from humans exposed to O. volvulus and E. histolytica. Such selective immune-regulatory capacity of IL-12 and IL-18 may comprise an important tool to re-direct polarized cytokine responses towards a balanced Th1/Th2 cytokine profile, which may prevent pathology and promote immunity against helminth and protozoan parasite infections.

Possible pathogenic pathways in the adverse clinical events seen following ivermectin administration to onchocerciasis patients

BACKGROUND: Reactions are commonly associated with the chemotherapy of onchocerciasis. However unmanageable reactions are uncommon when ivermectin (Mectizan(R)) is used for the treatment of this infection, and this drug has proved to be a great improvement over previously used agents. Serious adverse events (SAE) nevertheless have occurred, and there is considerable concern about the negative effect such events may have on mass drug administration programs.This paper reviews the basic pathogenic mechanisms that can be involved in the destruction of microfilaria by chemotherapeutic agents. A central challenge to filarial chemotherapy is the need to remove parasites from biologically sensitive tissues, a more difficult medical challenge than eliminating nematodes from the gastrointestinal tract.Explanations for the etiology of the serious adverse reactions occurring with ivermectin treatment in specific geographic areas where there is coincident heavy Loa loa infections are hampered by a lack of specific pathological case material. Ways to investigate these possibilities are reviewed. Possible pathogenic mechanisms include embolic vascular pathology accompanied by local inflammation, blood brain barrier mdr1 abnormalities, and genetic predisposition to excessive inflammatory responses. CONCLUSION: It is important to keep ivermectin, and all its associated adverse clinical events, in perspective with the many other chemotherapeutic agents in general use - many of which produce serious adverse events even more frequently than does ivermectin. Currently available evidence indicates that the pathogenesis of the Loa-associated adverse reactions are probably related to inflammatory responses to microfilariae in specific tissues. However, the possibility of genetic predispositions to pathology should also be considered.

CD4+-dependent immunity to Onchocerca volvulus third-stage larvae in humans and the mouse vaccination model: common ground and distinctions

Onchocerciasis is a major filarial disease and is the second most common cause of infectious blindness in the world. Disease development after infection with Onchocerca volvulus varies widely and is determined by the host's immune response to the parasite. Vector control and administration of ivermectin has reduced infection and disease rates significantly. However, limitations of these programmes, including ivermectin's selective activity on microfilariae, the need for 10-15 years of annual treatments, logistical obstacles and the potential emergence of drug-resistant strains demand alternative strategies. A vaccine that targets O. volvulus infective third-stage larvae (L3) could provide an additional tool to guarantee successful elimination of infection with O. volvulus. An essential step in the development of immunoprophylactic procedures and reagents is the identification of host immune responses toward antigens of O. volvulus L3 and L3 developing to the fourth-stage larvae that are associated with protection against these stages of the parasite. This review summarises the recent advancements in understanding the immune mechanisms in particular the CD4(+) responses to L3 stages in humans and in the mouse vaccination model. Comparison between the two uncovered common immunological elements in naturally exposed humans and mice vaccinated with radiation attenuated L3 or recombinant O. volvulus antigens, as well as significant differences. These studies promisingly suggest that the O. volvulus mouse model is a very useful adjunct to the studying of natural infection in humans and could provide us with the tools to identify the target molecules and the effector immune correlates of protection in humans responsible for attrition of L3 stages. Since some of these antigens may exist in other nematodes, any insight gained into the mechanisms of vaccine-induced anti-O. volvulus L3 protective immunity in both humans and mice could be applicable to the development of vaccines against other nematode infections.

Density-dependent parasite establishment suggests infection-associated immunosuppression as an important mechanism for parasite density regulation in onchocerciasis

The modulation of human immune response by filarial parasites has yielded contradictory experimental findings and attracted much controversy. We address the unresolved question of acquisition, establishment and accumulation of Onchocerca volvulus by using a modelling approach that relates computer simulations to cross-sectional data concerning parasite burdens in 913 West African onchocerciasis patients. It is shown that the acquisition of O. volvulus is not constant with host age; instead, the analysis of age profiles of parasite burdens strongly indicate the operation of immunosuppressive processes within the human host, associated with the presence of adult parasites or microfilariae. It is suggested that these processes suppress immunity against incoming infective larvae (L3), which themselves act as an immune modulating component once they have successfully overcome the barrier of concomitant immunity. Suppression of parasite-specific immunity leads to parasite establishment rates which increase along with the parasite burden, but which hardly depend on hyperendemic annual transmission potentials. Children, still immunocompetent due to low parasite burdens, acquire 0.1-0.5 adult female parasites per year, whereas older people, immunosuppressed due to high burdens, acquire 2-4 adult female parasites per year. Differences in parasite establishment between the forest and the savannah strains of O. volvulus are quantified and dynamic aspects of density-dependent parasite establishment discussed.

Interleukin-4 is essential for the control of microfilariae in murine infection with the filaria Litomosoides sigmodontis

Litomosoides sigmodontis is the only filaria which develops from infective larvae into microfilaria-producing adults in immunocompetent laboratory mice. In this study we report that interleukin-4 knockout (IL-4 KO) mice have an up to 100-fold-higher and a significantly prolonged microfilaremia compared to wild-type BALB/c mice, as well as 20 times more microfilariae in the thoracic cavity, the site of infection. While worm development and adult worm persistence were equivalent in IL-4 KO and wild-type mice, the fertility and length of adult female worms in IL-4 KO mice was clearly enhanced. The high susceptibility to microfilariae in IL-4 KO mice required the presence of adult worms in a full infection cycle since microfilariae loads did not differ much between IL-4 KO and wild-type mice when purified microfilariae were injected into mice. In addition, we found that eosinophilia was diminished and immunoglobulin E (IgE) was absent in IL-4 KO mice. IgE, however, does not seem to be the essential factor for microfilarial containment since microfilaremia was not elevated in B-cell KO mice. In conclusion, IL-4 is shown for the first time to be essential for the control of microfilarial loads but not of adult worm loads in a fully permissive murine filarial infection. IL-4 dependent effector pathways seem to operate on adult worms rather than directly on microfilariae.

Lack of interferon-γ confers impaired neutrophil granulocyte function and imparts prolonged survival of adult filarial worms in murine filariasis

We investigated the role of IFN-gamma in host defense during murine filariasis. Using the fully permissive infection of BALB/c mice with the rodent filaria Litomosoides sigmodontis, we show that interferon (IFN)-gamma is essential for encapsulation of adult filarial worms in inflammatory nodules and for normal worm clearance. IFN-gamma knockout (KO) mice had only one third of the nodules of wild-type mice but displayed a more than twofold increase in worm burden and increased microfilaremia. Neutrophil granulocytes, but not macrophages or eosinophils, appear to directly control worm load and nodule formation. Neutrophils, which we showed earlier to be essential for the encapsulation process in the thoracic cavity, where the worms reside, were diminished at this location in IFN-gamma KO compared to wild-type mice; they also displayed strongly reduced chemotactic and phagocytic activity compared to neutrophils of controls. This argues for a distinct defect in neutrophil activation accounting for the low formation of inflammatory nodules. Tumor necrosis factor-alpha, a major neutrophil-activating cytokine expressed by macrophages in the thoracic cavity around the worms, was highly induced in wild-type but absent in KO mice. Diminished activation of neutrophils seems to be a general hallmark of IFN-gamma KO mice, since neutrophils from uninfected KO mice also showed a reduction in chemotactic and phagocytic activity when induced by casein. In conclusion, these data are the first to define an IFN-gamma-dependent immune effector mechanism in murine filarial infection, i.e. neutrophil-mediated control of the adult worm load.

Human infection with Ascaris lumbricoides is associated with suppression of the interleukin-2 response to recombinant cholera toxin B subunit following vaccination with the live oral cholera vaccine CVD 103-HgR

To investigate the potential immunomodulatory effects of concurrent ascariasis on the cytokine response to a live oral vaccine, we measured cytokine responses to cholera toxin B subunit (CT-B) following vaccination with the live oral cholera vaccine CVD 103-HgR in Ascaris lumbricoides-infected subjects randomized in a double-blind study to receive two doses of either albendazole or placebo prior to vaccination and in a group of healthy U.S. controls. Postvaccination cytokine responses to CT-B were characterized by transient increases in the production of interleukin-2 (IL-2; P = 0.02) and gamma interferon (IFN-gamma; P = 0.001) in the three study groups combined; however, postvaccination increases in IFN-gamma were significant only in the albendazole-treated A. lumbricoides infection group (P = 0.008). Postvaccination levels of IL-2 were significantly greater in the albendazole-treated group compared with the placebo group (P = 0.03). No changes in levels of Th1 and Th2 cytokines in response to control ascaris antigens were observed over the same period. These findings indicate that vaccination with CVD 103-HgR is associated with a Th1 cytokine response (IL-2 and IFN-gamma) to CT-B, that infection with A. lumbricoides diminishes the magnitude of this response, and that albendazole treatment prior to vaccination was able to partially reverse the deficit in IL-2. The potential modulation of the immune response to oral vaccines by geohelminth parasites has important implications for the design of vaccination campaigns in geohelminth-endemic areas.

Prenatal immune priming with helminth infections: parasite-specific cellular reactivity and Th1 and Th2 cytokine responses in neonates

The present investigation aimed to determine to what extent maternal helminth infection primes parasite-specific cellular responsiveness in neonates. Umbilical cord mononuclear blood cells (UCBC) and peripheral blood mononuclear cells (PBMC) from mothers proliferated in response to mitogenic stimulation with concanavalin A, as well as to bacterial Streptococcus pyogenes-derived (streptolysin O) and helminth-specific antigens of Necator americanus and Onchocerca volvulus. Cellular responses to Echinococcus multilocularis (Em) and Oesophagostomum bifurcum (Oes), helminth parasites not endemic in the study area, were absent (for Em) or very low (for Oes due to antigenic cross-reactivity). Cellular responsiveness to mitogen and antigens was higher in mothers than in their neonates. Several Th1-type (IL-2, IL-12, and IFN-gamma) and Th2-type (IL-5 and IL-10) cytokines were produced by UCBC from neonates and PBMC from mothers. Low levels of IFN-gamma were elicited by UCBC in response to helminth and bacterial antigens, while secretion of IL-2 was pronounced and similarly high in neonates and their mothers. Amounts of IL-5 produced by UCBC in response to bacterial SL-O and mitogenic stimulation (PHA) were low, but equivalent levels of IL-5 were induced by intestinal helminth and filaria-derived antigens in neonates and mothers. A pronounced production of IL-10 and IL-12 by UCBC was observed--spontaneous IL-10 and IL-12 secretion by UCBC was higher in neonates than by PBMC from mothers. Net amounts of IL-10 elicited by helminth antigens were similar, while net IL-12 in response to mitogen, and bacterial and helminth antigens was significantly higher in mothers than their offspring. Our results indicate that human maternal helminth infection does sensitize in utero for parasite-specific cellular responsiveness in offspring, and also activates specific production of several cytokines, and such children do not present a dominant expression of immunity of either Th1 or Th2.

The role of nitric oxide in the innate resistance to microfilariae of Litomosoides sigmodontis in mice

Nitric oxide (NO) has been shown to be an important effector mechanism in the defence against various pathogens, including filariae. The production of NO, as well as H2O2, is induced by the Th1 cytokine IFN-gamma. Therefore, the microfilariae (mf) of filarial nematodes, which are known to elicit the release of IFN-gamma, may be a target of NO release. In this study, we found that mf of the filarial species Litomosoides sigmodontis were resistant to the attack of H2O2, but vulnerable to NO exposure in vitro by a chemical NO donor, as well as activated macrophages. Adult worms were considerably less affected by exposure to NO. In-vivo production of NO following injection of mf, in this and previous studies, suggested a central role in the defence to filariae. However, neither pharmaceutical inhibition of nitric oxide synthesis, nor genetic knockout of the gene for inducible nitric oxide synthase (iNOS), abrogated resistance to circulating mf in mice. Interestingly, however, iNOS-KO mice showed higher interleukin (IL)-2 responses and lower IL-10 production, compared to their wild-type counterparts. In conclusion, despite its effectiveness in vitro and the observed production of NO by ex vivo cells following infection, nitric oxide seems not to be an important factor in elimination of mf of L. sigmodontis in vivo. However, it may have a regulatory role in the immune response.

Measurement of T-cell-derived antigen binding molecules and immunoglobulin G specific to Candida albicans mannan in sera of patients with recurrent vulvovaginal candidiasis

Immunoglobulin G (IgG) and T-cell-derived antigen binding molecules (TABM) specific to whole Candida extract and to Candida-derived mannans prepared by both the cetryltrimethylammonium bromide (CTAB) and alkaline degradation (PEAT) methods were measured in the sera of women with vulvovaginal candidiasis and controls. In the patients there were significantly higher levels of IgG to both CTAB and PEAT mannans and of TABM to CTAB mannan. TABM specific to CTAB mannan was purified from the serum of a patient with a high titer of this TABM. The purified TABM bound specifically to CTAB mannan and to other yeast and mold extracts. This TABM preparation was associated with transforming growth factor beta2 (TGF-beta2), and on specific binding to mannan there was a marked increase in the level of detectable TGF-beta2. This increase in TGF-beta2 level was critically dependent on the relative concentrations of the purified TABM and mannan, being smallest when either was in excess. The TABM specific to CTAB mannan was also shown to inhibit Candida-stimulated gamma interferon production. The results suggest that CTAB mannan-specific TABM may increase susceptibility to vulvovaginal candidiasis in association with a shift in the immune response to the Th2 type.

Antigen-specific cellular hyporesponsiveness in a chronic human helminth infection is mediated by T(h)3/T(r)1-type cytokines IL-10 and transforming growth factor-beta but not by a T(h)1 to T(h)2 shift

Exposure to infective larvae of the filarial nematode Onchocerca volvulus (Ov) either results in patent infection (microfilaridermia) or it leads to a status called putative immunity, characterized by resistance to infection. Similar to other chronic helminth infections, there is a T cell proliferative hyporesponsiveness to Ov antigen (OvAg) by peripheral blood mononuclear cells (PBMC) from individuals with patent infection, i.e. generalized onchocerciasis (GEO), compared to PBMC from putatively immune (PI) individuals. In this study, mechanisms mediating this cellular hyporesponsiveness in GEO were investigated: the low proliferative response in PBMC from GEO individuals was associated with a lack of IL-4 production and significantly lower production of IL-5 compared to those from PI individuals, arguing against a general shift towards a T(h)2 response being the cause of hyporesponsiveness. In contrast, IL-10 and transforming growth factor (TGF)-beta, two cytokines associated with a T(h)3 response, seemed to mediate hyporesponsiveness: PBMC from individuals with GEO produced significantly more IL-10, and T cell proliferative hyporesponsiveness in this group could be reversed by the addition of anti-IL-10 and anti-TGF-beta antibodies. Hyporesponsiveness was specific for OvAg and not observed upon stimulation with related nematode antigens, arguing for a T cell-mediated, Ov-specific down-regulation. Ov-specific T cells could be cloned from GEO PBMC which have a unique cytokine profile (no IL-2 but high IL-10 and/or TGF-beta production), similar to the T cell subsets known to suppress ongoing inflammation (T(h)3 and T(r)1), indicating that this cell type which has not been found so far in infectious diseases may be involved in maintaining Ov-specific hyporesponsiveness.

Cytokine and chemokine secretion by human peripheral blood cells in response to viable Echinococcus multilocularis metacestode vesicles

In human alveolar echinococcosis, asexually proliferating metacestodes of Echinococcus multilocularis progressively infiltrate host tissues and cause serious pathology to the affected organs. This study employed an in vitro culture of E. multilocularis and examined the production of cytokines and chemokines by peripheral blood cells from echinococcosis patients in response to viable proliferating E. multilocularis metacestode vesicles (Em-vesicles). A significant interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) production was elicited in echinococcosis patients when their cells were cocultured with viable Em-vesicles and autologous immune sera. Furthermore, in echinococcosis patients, substantial amounts of cytokines were detected; and the levels of IL-12 and IL-13 found in patients correlated with the actual state of clinical disease. These observations suggest that viable E. multilocularis vesicles will induce significant cellular production of cytokines and chemokines in patients, and that such immune mediators may activate and enhance antibody-dependent cellular effector mechanism against proliferating metacestodes of E. multilocularis.

Prenatal immune priming in onchocerciasis-onchocerca volvulus-specific cellular responsiveness and cytokine production in newborns from infected mothers

This study investigated the effect of maternal Onchocerca volvulus infection on humoral and cellular responsiveness in newborn children and their mothers. Onchocerca volvulus-specific IgG isotypes and IgE were significantly elevated in infected mothers and their infants. One year post partum, O. volvulus-specific IgG4 was strongly reduced in children of infected mothers, while IgG1 responses weakened only slightly. Umbilical cord mononuclear blood cells (UCBC) and peripheral blood cells (PBMC) from mothers proliferated in response to phytohaemagglutinin (PHA), concanavalin A (Con A), and the bacterial antigens streptolysin-O (SL-O) or purified protein derivative (PPD). UCBC from neonates born to O. volvulus-infected mothers responded lower (P < 0.01) to Con A (at 5 micrograms/ml), PPD (at 10 and 50 micrograms/ml) and O. volvulus-derived antigens (OvAg) (at 35 micrograms/ml), and in parallel, a diminished cellular reactivity (P < 0.01) by PBMC was observed to OvAg in mothers positive for O. volvulus. Several Th1-type (IL-2, IL-12, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha)) and Th2-type (IL-4, IL-5, IL-10, IL-13) cytokines were secreted by UCBC and PBMC in response to OvAg, bacterial SL-O and PHA. OvAg did not stimulate IL-2 and none of the mitogens or antigens induced production of IL-4 in neonates. In response to OvAg, substantially elevated (P < 0.01) amounts of IFN-gamma were produced by UCBC from newborns of O. volvulus-infected mothers. UCBC secreted low levels of IL-5 and IL-13, while higher amounts of IL-10 were found (P < 0. 01) in newborns from onchocerciasis-free mothers. In conclusion, maternal O. volvulus-infection will sensitize in utero parasite-specific cellular immune responsiveness in neonates and activate OvAg-specific production of several Th1- and Th2-type cytokines.

Regulatory effects of Th1-type (IFN-gamma, IL-12) and Th2-type cytokines (IL-10, IL-13) on parasite-specific cellular responsiveness in Onchocerca volvulus-infected humans and exposed endemic controls

The present study investigated in vitro the regulatory effects of T helper 1 (Th1)-type (interferon-gamma, IFN-gamma; interleukin-12, IL-12) and Th2-type cytokines (IL-10, IL-13) on Onchocerca volvulus-specific cellular reactivity in onchocerciasis patients, and in exposed endemic control individuals presenting no clinical and parasitological signs of disease. In both patients and controls, addition of IL-10 dose-dependently depressed O. volvulus antigen (OvAg)-specific cellular proliferation, and peripheral blood mononuclear cells (PBMC) from patients who were more sensitive to the suppressive effect of IL-10 than those from endemic controls. However, neutralization of IL-10 by specific antibody did not reverse cellular hyporesponsiveness. In contrast to the inhibitory effects of IL-10, exogenous IL-12 and IL-13 augmented PBMC proliferative responses to OvAg both in patients and controls (P<0. 01) and neutralizing of IL-12 or IL-13 significantly decreased OvAg-specific proliferation in both groups. Exogenous IFN-gamma did not activate OvAg-specific proliferative responses in patients, but anti-IFN-gamma antibodies abolished cellular reactivity to OvAg. Antibody to IL-10 increased (P<0.05) OvAg-specific production of IL-5, IL-12 and IFN-gamma, and inversely, anti-IFN-gamma enhanced IL-10 (in patients only) and IL-5 and IL-13 in both patients and controls. Neutralization of IL-12 activated OvAg-specific production of IL-10, IL-2 and IFN-gamma. In conclusion, despite of an overproduction of IL-10, which suppressed cellular reactivity in patients and control individuals, OvAg-specific cellular responses were activated in vitro by exogenous supplementation with IL-12 and IL-13, and cytokine neutralization experiments confirmed that distinct type 1 and type 2 T helper cytokines cross-regulate expression and magnitude of O. volvulus-specific cellular responsiveness in humans.

Crusted scabies in two immunocompromised children: successful treatment with oral ivermectin

Two immunodeficient children, aged 4 and 12 years, with crusted scabies were successfully treated with a single oral dose of ivermectin (200 micrograms/kg). One child had been diagnosed in infancy with an undefined congenital T cell immunodeficiency and the other with chronic mucocutaneous candidiasis. Both had failed to respond to conventional topical therapy. In view of the excellent therapeutic response and absence of side-effects, ivermectin should be considered in the treatment of recalcitrant crusted scabies in children.

Delayed-type hypersensitivity reactions to Onchocerca volvulus antigens in exposed and non-exposed African individuals

Although considered of critical importance, the mode of helper T-lymphocyte function in Onchocerca volvulus infection is still unclear including the role of the Th1/Th2 dichotomy. We studied the delayed-type hypersensitivity (DTH) reaction, which is the classical Th1 response, to O. volvulus antigens in Africans exposed and not exposed to the infection. DTH reactions were found in a small percentage of patients with generalized onchocerciasis, but in a high percentage of patients with localized onchocerciasis, in putatively immune subjects, and also in non-exposed individuals, which may be due to cross-reactivity with other nematodes. These findings support the notions of (i) prenatal influence of maternal O. volvulus infection preventing development of Th1 responses and/or (ii) suppression of Th1 responses by the infection itself.

Decreased CD4 and increased CD8 counts with T cell activation is associated with chronic helminth infection

We have previously reported the presence of marked immune dysregulation with a dominant Th2 profile, in a population of Ethiopian immigrants (ETH) in Israel heavily infected with helminths. In order to characterize better this immune dysregulation we studied by flow cytometry the expression of several activation markers on peripheral T cell populations, and lymphocyte apoptosis, in blood samples obtained from 63 'new' ETH (recently arrived), 18 'old' ETH (> 5 years since immigration) and 34 non-Ethiopian Israelis. The main findings in the 'new' ETH group in comparison with the non-Ethiopian controls were: (i) decreased CD4 and increased CD8 lymphocyte counts; (ii) elevated levels of activated T cells (CD3, CD4 and CD8) expressing HLA-DR; (iii) decreased levels of 'naive' CD4+ cells (CD45RA+), with increased levels of 'memory' CD4+ cells (CD45RO+); (iv) decreased numbers of CD28+ CD8+ lymphocytes; (v) marked increase in lymphocyte apoptosis. These T cell alterations and activation profile remained unchanged in 10 'new' ETH in whom the helminth infections persisted for 6-11 months. In contrast, in 18 'old' ETH, without helminth infections, the T cell activation profile was within the normal range. These findings suggest that chronic helminth infections may have a profound effect on the immune system of the host that disappears after eradication of these infections and adjustment to the new environment. It should therefore be taken into consideration for every immunomodulation therapy and especially in vaccine design and trials, in regions endemic for helminth infections.

T cell responses in coinfection with Onchocerca volvulus and the human immunodeficiency virus type 1

Onchocerca volvulus and the human immunodeficiency virus (HIV) are two immunocompromising infectious agents of major public health concern in Uganda. To examine the effect of coinfection with O. volvulus and HIV on cellular immune responses, lymphocyte proliferative responses and cytokine production of peripheral blood mononuclear cells (PBMC) from persons infected with O. volvulus with and without HIV type 1 infection were compared. Proliferation of PBMC to PHA and tuberculin (PPD) in coinfection was less (P = 0.08, P < 0.01) than in O. volvulus infection. O. volvulus extract stimulated lymphocyte proliferation in microfilaria-negative and HIV-negative O. volvulus infection while only an inconspicuous response was observed in microfilaria-negative coinfection. After stimulation of PBMC with PPD, the production of interferon-gamma (IFN-gamma), interleukin (IL)-4 and IL-5-demonstrated in O. volvulus infection-were reduced in coinfection with HIV (P < 0.01). While both groups failed to produce IFN-gamma in response to O. volvulus extract, only O. volvulus infected persons generated pronounced IL-5 and low IL-4 levels (0.01 > P = 0.02). The cellular immune responses in coinfection suggested an HIV-related lack of specific reactivity to O. volvulus antigen and impairment of IL-4 and IL-5 production in addition to the lack of IFN-gamma response on antigenic stimulation.

Immune responses to third stage larvae of Onchocerca volvulus in interferon-gamma and interleukin-4 knockout mice

To shed clarity on the dichotomy of reported results relative to the significance of T helper-1 vs T helper-2 immune responses in onchocerciasis, we compared the survivability of Onchocerca volvulus third-stage larvae (L3) in immunized mice that had either a targeted disruption of the Interleukin-4 or Interferon-gamma gene. Treatment groups consisted of control mice and mice immunized with irradiated O. volvulus L3. All mice were challenged with diffusion chambers containing viable L3. Vaccinated IL-4-/- were unable to kill this larval target. In contrast, vaccinated INF-gamma-/- and C57BL/6 mice, exhibited high levels of killing, had elevated levels of IL-4 and significantly greater numbers of eosinophils in their diffusion chambers than the IL-4-/-. Whereas, levels of IFN-gamma in all three groups of immunized mice were equivalent to those of control mice, levels of IL-5 were elevated, even in the IL-4-/-, indicating that cytokines other than IL-4 were involved in its production. The protective immune response to third-stage larvae of O. volvulus in mice vaccinated with irradiated larvae has an absolute IL-4 requirement.

Onchocera volvulus: characterization of a highly immunogenic Gln-rich protein

A pool of sera from individuals classified as putatively immune (PI) to Onchocerca volvulus infection was employed in the screening of a fourth-stage larval cDNA expression library. A highly immunogenic clone, encoding the Ov 53/80 protein, was identified. The full length cDNA of clone 4.21 contained 2527 nucleotides encoding 769 amino acids of which 100 are glutamine residues (13%). Antibodies raised against recombinant protein encoded by a partial cDNA sequence (clone 73-k) recognized a 53 and 80 kDa protein in O. volvulus larval and adult parasite extracts, respectively. The antibodies localized the native protein in the cuticle, hypodermis, secretory vesicles and in granules of the glandular esophagus of larvae and in the hypodermis and the cuticle of adult worms. The recombinant 73-k polypeptide (r73) was recognized by 90-100% of sera from PI and infected individuals from Liberia, but only by 67% of similar groups from Ecuador. r73 specific IgG2 and IgG3 levels in the PI from Liberia and Ecuador, respectively, were significantly lower than in the infected, whereas the r73 specific IgG1/IgG3 or IgG1/IgG2 in the PI and the infected individuals from Liberia or Ecuador, respectively, were similar. The IgG4 specific antibody response in the PI from Liberia and Ecuador were lower than in the infected. The T-cell proliferative responses to r73 in infected individuals from Cameroon were found to be inversely correlated with their levels of microfilariae.

Protective responses against skin-dwelling microfilariae of Onchocerca lienalis in severe combined immunodeficient mice

Inoculation of severe combined immunodeficient (SCID) mice with microfilariae of Onchocerca lienalis results in a sustained infection of the skin, extending for months beyond the point at which the parasites are eliminated from immunocompetent BALB/c controls. Reconstitution of SCID mice with spleen cells, thymocytes, or CD4+-cell-enriched splenocytes from naive BALB/c donors confers the ability to mount a protective immune response, leading to the rapid elimination of microfilariae. High levels of interleukin-5 and low levels of gamma interferon in the sera of reconstituted SCID mice during the destruction of microfilariae suggest that this protective immune response is directed by Th2 lymphocytes, mirroring that observed in immunocompetent controls. Unexpectedly, abbreviation of primary infections of unreconstituted SCID mice with the drug ivermectin induces resistance to reinfection with microfilariae at a level equivalent to that induced in secondarily infected, immunocompetent controls. In contrast to protection mediated by adoptive reconstitution, resistance induced by ivermectin-abbreviated infection occurs in the absence of T cells and in association with negligible levels of serum interleukin-5 and gamma interferon. This points to the activation of some alternative host defense mechanism that operates after the clearance of therapeutic levels of drug. Such a response could have important implications for the treatment of human onchocerciasis and may go some way in explaining the long-term suppression of microfilariae observed in patients after treatment with ivermectin.

Experimental infection of a nonhuman primate with Loa loa induces transient strong immune activation followed by peripheral unresponsiveness of helper T cells

Human infection with the parasite Loa loa is characterized by a good adaptation between the parasite and its host. One portion of the human population harbors only adult worms in subcutaneous tissues, whereas another portion also harbors the L1 microfilarial stage in peripheral circulation. This study was undertaken to understand the mechanisms by which the parasite evades or modulates host immunological attack. The cellular responses, based on T-cell proliferation, to the production of various cytokines (interleukin-2 [IL-2], gamma interferon [IFN-gamma], IL-4, and IL-5) and to expression of cytokine (IL-2, IFN-gamma, IL-4, IL-5, IL-10, and IL-12) mRNAs were investigated during the experimental infection with human parasite L. loa of a nonhuman primate which has been shown to display a spectrum of disease similar to that found in humans. Our results indicate that a T-cell unresponsiveness occurs when female worm products are released into the peripheral circulation, preceded by a transient period of strong T-cell proliferation, cytokine production, and cytokine mRNA expression. In the unresponsive state, only IL-10 mRNA is expressed, suggesting a role for IL-10 in down-regulation and maintenance of unresponsiveness. Taken together, these results indicate that both IL-10 production, which is known to inhibit B7 expression on monocytes, and the massive release of female products in the blood where T cells encounter antigens presented by nonactivated B lymphocytes, which lack costimulatory signals, should contribute to the inactivation of T cells.

The diverse expression of immunity in humans at distinct states of Onchocerca volvulus infection

This study examined the development and persistence of immunity in humans presenting defined states of Onchocerca volvulus infection, i.e. in exposed endemic control individuals without microfilaridermia and clinical disease, in patients with patent or post-patent onchocerciasis, and in patients concurrently infected with Mansonella perstans. Onchocerca volvulus antigen (OvAg)-specific cellular reactivity was significantly diminished in microfilariae (mf)-positive patients, while the highest reactivity was measured in exposed but mf-negative endemic controls, those being free of any clinical signs of onchocercal disease. In patients who became post-patent, responses to OvAg were significantly augmented, but did not approach entirely the magnitude observed in endemic controls. In onchocerciasis patients with concurrent mansonelliasis, cellular unresponsiveness to OvAg persisted, even when mf of O. volvulus were eliminated permanently by repeated ivermectin therapy. Cells from mf-positive onchocerciasis patients produced significantly less interferon-gamma (IFN-gamma) (P < 0.01) and interleukin-5 (IL-5) (P < 0.05) in response to OvAg than those taken from endemic controls or post-patent individuals in whom IFN-gamma and IL-5 production was similarly high. In contrast, both OvAg-driven as well as spontaneous IL-10 secretion was higher in mf-positive patients than in endemic controls or post-patent cases. In all individuals examined, serological recognition of OvAg by immunoglobulins was dominated by IgG4; in mf-positive patients OvAg of 205,000-12,000 molecular weight (MW) were strongly bound. In post-patent individuals, and similarly in endemic controls. OvAg recognition by IgG4 varied from intense (with numerous antigens being recognized) to weak or absent antigen binding. Significantly elevated OvAg-specific IgG isotypes were measured in mf-positive onchocerciasis patients in comparison with endemic controls or post-patent individuals (with the exception of IgG3). IgG1, IgG2 and IgE were higher, but IgG4 was lower in endemic controls compared with post-patent onchocerciasis patients. The ratios of IgG4/IgG1 differed (P < 0.001) between endemic controls and mf-positive or post-patent onchocerciasis patients, with IgG4/IgG1 ratios of R < 3.0 being characteristic for endemic controls and post-patent O. volvulus infection. In conclusion, this cross-sectional immunoepidemiological investigation showed that distinct states of O. volvulus infection correlate with a particular cellular and humoral immune response. The mf-free condition appeared to be associated with a vigorous parasite-specific cellular reactivity and a particular cytokine production profile, while concurrent M. perstans infection depressed OvAg-specific cellular responsiveness. Antibody responses, in all likelihood, reflected the intensity and state of infection, and not the degree of acquired immunity protective against parasite aggregation.

Microfilarial clearance in loiasis involves elevation of Th1 and Th2 products and emergence of a specific pattern of T-cell populations

Diethylcarbamazine (DEC) induced clearance of microfilaraemia in loiasis is associated with severe posttreatment reactions. To define the switch from hypo- to hyper-responsiveness associated with DEC treatment, phenotypic alterations of T-lymphocytes, characterized by flow cytometry, and cytokines, determined by enzyme linked immunosorbent assay, were monitored in a microfilaraemic patient. In contrast to reports on onchocerciasis and lymphatic filariases, no elevation of interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha was observed. The most severe side effects coincided with an elevation of interferon (IFN)-gamma on day 3, followed by IL-10, transforming growth factor (TGF)-beta 2 and macrophage inflammatory protein-1 alpha (MIP-1 alpha) peaking on day 5. Phenotypically, T-cell activation markers CD38, CD54 and CD25 were significantly expressed before treatment, with high CD38 expression still existing one year after clearance of microfilaraemia. Treatment-related increases were observed with anti-CD122, anti-HLA-DR and anti-CD69. CD28 was expressed before treatment on almost 100% of CD4+ and CD8+ T cells and dropped to 20% by day 5, reaching again baseline levels on day 21. Furthermore, there emerged 20% TCR alpha beta+/CD3+ T cells and 10% anti-beta V5(c)+ T cells, altogether indicating a specific pattern of T-helper (Th) 1 and Th2 cytokines as well as expansion of certain pauciclonal T-cell populations in response to microfilarial clearance.

Anti-interleukin-4 modulation of the Th2 polarized response to the parasitic nematode Brugia pahangi

Lymphatic filariasis is a chronic disease characterized by a pronounced Th2 bias in the immune response and impaired antigen (Ag)-specific Th1 responses. We have used a mouse model of filariasis to investigate the role of the infective form (the third-stage larvae [L3]) in modulating the immune response. Subcutaneous infection of BALB/c mice with L3 of Brugia pahangi has a profound effect on Th cell function. By day 12 post-infection, spleen cells from these mice exhibited a dramatic reduction in concanavalin A-driven proliferation and interleukin-2 (IL-2) and gamma interferon (IFN-gamma) secretion in comparison with uninfected controls. However, exposure to L3 did not render the mice completely unresponsive; these animals mounted a strong Th2 response to the parasite, characterized by elevated levels of IL-4, IL-5, and IL-10 and parasite-specific serum immunoglobulin G (IgG), IgG1, and IgE. Treatment of spleen cells from L3-infected mice with neutralizing anti-IL-4 or recombinant IL-2 resulted in a dramatic increase in concanavalin A-induced proliferation and IL-2 and IFN-gamma production. Despite their defective polyclonal Th1 response, cells from L3 infected mice proliferated when stimulated with Ag, and this response was blocked by anti-IL-4. However, anti-IL-4 treatment failed to induce Ag-specific IL-2 or IFN-gamma production, indicating that B.pahangi-primed Th1 cells do not appear to be present or are still unable to respond even in the absence of IL-4.

Elevated proliferation and interleukin-4 release from CD4+ cells after chemotherapy in human Schistosoma haematobium infection

Cellular immune responses to schistosomal antigens were examined in 110 Schistosoma haematobium-infected individuals before and 5 weeks after treatment with praziquantel. Chemotherapy resulted in significant decrease in worm load as measured by egg output and circulating antigens. The proliferative responses to adult worm antigen (AWA) increased significantly after treatment (p < 0.001) whereas purified protein derivative of tuberculin or phytohemagglutinin responsiveness was unaffected. Interleukin (IL)-4 production in response to both AWA and soluble egg antigen (SEA) increased markedly after treatment (p < 0.001), but IL-5 remained unchanged. None of the studied subjects released any measurable IL-2 and only 21% produced interferon (IFN)-gamma in response to parasite antigens. The deficiency in either IFN-gamma or IL-2 release was not restored by chemotherapy. Thus chronic infection with S. haematobium is associated with the reversible down-regulation of T cell proliferative responses and IL-4 release. Results from cell depletion experiments indicated that CD4+ T cells were the target of this down-modulation.

Malaria and onchocerciasis: On HLA and related matters

In recent years, associations of particular factors of the human leukocyte antigen (HLA) system with two major infectious diseases of tropical countries have been recognized: common West African HLA antigens are associated with protection from severe Plasmodium falciparum malaria, and HLA-D alleles are associated with generalized disease, localized disease and putative immunity in Onchocerca volvulus infection. Here, Christian Meyer and Peter Kremsner summarize current information on the involvement of HLA factors in P. falciparum malaria and O. volvulus infection, and briefly report on HLA-related immunological characteristics of various conditions in these infectious diseases.

Eosinophils are the major effector cells of immunity to microfilariae in a mouse model of onchocerciasis

Mice inoculated with microfilariae of the filarial nematode Onchocerca lienalis clear their parasites over a period of 3-4 months and are highly resistant to re-infection. We have investigated the comparative roles of the eosinophil, macrophage and neutrophil in effecting this parasite clearance, employing agents specifically to perturb cell function in vivo. Using the anti-IL-5 monoclonal antibody TRFK-5, we show that eosinophils are of primary importance in effecting resistance to re-infection. Ablation of macrophages (with carbon) and neutrophils (with the monoclonal antibody NIMP-R14) had no effect on parasite clearance following re-infection. Neutralization of these 3 cell types during a primary infection showed that while the removal of both eosinophils and macrophages caused a small but significant delay in parasite clearance, the depletion of neutrophils had no effect. This report describes the first direct evidence for eosinophil-mediated killing of microfilariae in vivo, and is consistent with Th-2 cell responses previously described in this model.

Susceptibility of Brugia malayi and Onchocerca lienalis microfilariae to nitric oxide and hydrogen peroxide in cell-free culture and from IFN gamma-activated macrophages

The susceptibility of Brugia malayi and Onchocerca lienalis microfilariae to H2O2 and NO either in cell-free culture or from IFN gamma-activated macrophages was examined. In cell-free culture, O. lienalis microfilariae were highly susceptible to H2O2 induced toxicity, exhibiting rapid reductions in motility and viability. The addition of exogenous catalase abrogated H2O2-induced killing. In contrast, B. malayi microfilariae were relatively resistant to H2O2, with concentrations as high as 50 microM having no effect on motility or viability. On exposure to NO, both species showed reductions in motility within 5-30 min, but longer was required to see effects on the viability of microfilariae. Parasites incubated with IFN gamma-activated macrophages also exhibited marked reductions in motility and viability. In cultures with B. malayi and activated macrophages, inhibition of these effects was achieved by the addition of either L-NMMA, to abolish NO production, or neutralizing anti-TNF alpha antibodies. Attempts to inhibit parasite killing by the addition of catalase to macrophage cultures were ineffective. The results of this study show that B. malayi and O. lienalis microfilariae have different susceptibility to H2O2, but are equally affected by exposure to NO. Moreover both species are killed by IFN gamma-activated macrophages and in the case of B. malayi, killing is dependent on the generation of NO via TNF alpha.

In Th2-biased lymphatic filarial patients, responses to purified protein derivative of Mycobacterium tuberculosis remain Th1

Natural infection with filarial nematode parasites results in immune responses skewed towards T helper (Th)2, while infection with mycobacteria shows many characteristics of a Th1-dominated response. Cytokines typifying Th1, interferon (IFN)-gamma, and Th2, interleukin (IL)-4, were measured following stimulation of peripheral blood mononuclear cells from filarial patients with Brugia malayi adult worm antigen (BmA) and purified protein derivative of Mycobacterium tuberculosis (PPD). In response to PPD, only 1 out of 81 patients produced IL-4, and this at an amount (4.4 pg/ml) just above the detection limit, whereas 59% of patients responded to BmA by releasing IL-4. Conversely, substantial quantities of IFN-gamma were released in response to PPD (geometric mean 37.43 U/ml) compared to low BmA-stimulated IFN-gamma production in the same patients (geometric mean 5.02 U/ml). These results demonstrate that the strong skewing of the cytokine environment towards Th2 in filarial patients in vivo does not influence the predominance of a Th1 type immune response to PPD.