Patterns of integration of DNA microinjected into cultured mammalian cells: evidence for homologous recombination between injected plasmid DNA molecules

We examined the fate of DNA microinjected into nuclei of cultured mammalian cells. The sequence composition and the physical form of the vector carrying the selectable gene affected the efficiency of DNA-mediated transformation. Introduction of sequences near the simian virus 40 origin of DNA replication or in the long terminal repeat of avian sarcoma provirus into a recombinant plasmid containing the herpes simplex virus thymidine kinase gene. (pBR322/HSV-tk) enhanced the frequency of transformation of LMtk- and RAT-2tk- cells to the TK+ phenotype 20- to 40-fold. In cells receiving injections of only a few plasmid DNA molecules, the transformation frequency was 40-fold higher after injection of linear molecules than after injection of supercoiled molecules. By controlling the number of gene copies injected into a recipient cell, we could obtain transformants containing a single copy or as many as 50 to 100 copies of the selectable gene. Multiple copies of the transforming gene were not scattered throughout the host genome but were integrated as a concatemer at one or a very few sites in the host chromosome. Independent transformants contained the donated genes in different chromosomes. The orientation of the gene copies within the concatemer was not random; rather, the copies were organized as tandem head-to-tail arrays. By analyzing transformants obtained by coinjecting two vectors which were identical except that in one a portion of the vector was inverted, we were able to conclude that the head-to-tail concatemers were generated predominantly by homologous recombination. Surprisingly, these head-to-tail concatemers were found in transformants obtained by injecting either supercoiled or linear plasmid DNA. Even though we demonstrated that cultured mammalian cells contain the enzymes for ligating two DNA molecules very efficiently irrespective of the sequences or topology at their ends, we found that even linear plasmid DNA was recruited into the concatemer by homologous recombination.

Biophysical characterization of fungal phytases (myo-inositol hexakisphosphate phosphohydrolases): molecular size, glycosylation pattern, and engineering of proteolytic resistance

Phytases (myo-inositol hexakisphosphate phosphohydrolases) are found naturally in plants and microorganisms, particularly fungi. Interest in these enzymes has been stimulated by the fact that phytase supplements increase the availability of phosphorus in pig and poultry feed and thereby reduce environmental pollution due to excess phosphate excretion in areas where there is intensive livestock production. The wild-type phytases from six different fungi, Aspergillus niger, Aspergillus terreus, Aspergillus fumigatus, Emericella nidulans, Myceliophthora thermophila, and Talaromyces thermophilus, were overexpressed in either filamentous fungi or yeasts and purified, and their biophysical properties were compared with those of a phytase from Escherichia coli. All of the phytases examined are monomeric proteins. While E. coli phytase is a nonglycosylated enzyme, the glycosylation patterns of the fungal phytases proved to be highly variable, differing for individual phytases, for a given phytase produced in different expression systems, and for individual batches of a given phytase produced in a particular expression system. Whereas the extents of glycosylation were moderate when the fungal phytases were expressed in filamentous fungi, they were excessive when the phytases were expressed in yeasts. However, the different extents of glycosylation had no effect on the specific activity, the thermostability, or the refolding properties of individual phytases. When expressed in A. niger, several fungal phytases were susceptible to limited proteolysis by proteases present in the culture supernatant. N-terminal sequencing of the fragments revealed that cleavage invariably occurred at exposed loops on the surface of the molecule. Site-directed mutagenesis of A. fumigatus and E. nidulans phytases at the cleavage sites yielded mutants that were considerably more resistant to proteolytic attack. Therefore, engineering of exposed surface loops may be a strategy for improving phytase stability during feed processing and in the digestive tract.

The cloning and reintroduction into animal cells of a functional CAD gene, a dominant amplifiable genetic marker

Rodent cells resistant to PALA, a specific inhibitor of the aspartate transcarbamylase activity of the multifunctional CAD protein, overproduce CAD as a result of amplification of the CAD gene. We cloned a functional CAD gene from Syrian hamster cells using a cosmid vector. Two independently isolated cosmids containing CAD genes have inserts 40 and 45 kb long. We introduced the cloned genes into CAD-deficient Chinese hamster ovary (CHO) cell mutants by fusing them with protoplasts of Escherichia coli containing the cosmids. We also introduced the cloned genes into wild-type CHO cells by selecting cells that became resistant to high concentrations of PALA following protoplast fusion. The transformants of the mutant and wild-type CHO cells contain multiple active copies of the donated Syrian hamster CAD genes. The cloned genes in three independent transformants are integrated into host-cell chromosomes at single locations identified by in situ hybridization. In two of these transformants, the genes are located in one X chromosome or in a chromosome resembling the X. In the third case, the genes are located in a small metacentric or rearranged chromosome.

Dental units: an environmental study of sources of potentially pathogenic mycobacteria

SETTING

Infections caused by non-tuberculous mycobacteria (NTM) are generally thought to be acquired from environmental sources. However, little is known about the situations in which transmission occurs.

OBJECTIVE

In an attempt to identify situations of relevant contact with NTM we investigated the water to which patients are exposed during dental treatment.

DESIGN

The concentration and species of NTM were determined in 43 cooling and spray water samples from 21 dental units in ten offices. In addition, mycobacterial colonization of 16 biofilm samples from the waterlines of two dental units was investigated.

RESULTS

The mean NTM concentration in the water samples was 365 colony-forming units (cfu) per mL, exceeding the mean drinking water concentration by a factor of almost 400. In the biofilm samples the mean NTM density amounted to 1165 cfu/cm2. The species identified included Mycobacterium gordonae, M. flavescens, M. chelonae, 'M. chelonae-like organism' and M. simiae.

CONCLUSION

High numbers of NTM may be swallowed, inhaled or inoculated into oral wounds during dental treatment, possibly resulting in colonization, sensitization or infection. Mycobacterial proliferation in biofilms forming within dental units may explain the extent of NTM contamination of dental spray and cooling water.

Onchocerca ochengi: epidemiological evidence of cross-protection against Onchocerca volvulus in man

In North Cameroon, the vector of Onchocerca volvulus (causative agent of human onchocerciasis) also transmits 2 filariae of animals: O. ochengi from cattle and O. ramachandrini from wart hogs. In order to assess the qualitative and quantitative roles of these 'animal filariae' in the epidemiology of O. volvulus, the transmission of the 3 parasites was measured in 2 villages and related to the endemicity of human onchocerciasis. In Galim, a cattle-farming Guinea savanna village where wild animals are rare, the overwhelming majority of all filarial infections found in the Simulium damnosum s.l. vectors throughout the year were O. ochengi (89%). The remaining infections were mainly O. volvulus (10.5%), and a few O. ramachandrini (0.5%). In Karna, a crop-farming Sudan savanna village where cattle are rare, but wild animals common, flies were also more frequently infected with animal filariae than with the human parasite. In the dry season, when nomadic cattle are present, 54% of all infections were O. ochengi, 36% O. volvulus and 10% O. ramachindrini. In the rainy season, when the cattle move away, flies were mainly infected with O. ramachandrini (52% of all infections) and secondly with O. volvulus (48%). In Karna, the relationship between the Annual Transmission Potential (ATP) of O. volvulus and its prevalence in the human population conformed to other onchocerciasis foci, in that a moderate ATP led to hyperendemic onchocerciasis. In Galim, however, a 7-fold higher O. volvulus-ATP (caused by a very high biting rate of the flies) contrasted with a strikingly low endemicity of onchocerciasis. Since, at the same time, in Galim the transmission of O. ochengi (measured on man) was very high (15,000 L3/fly collector/year), we hypothesize that the reduced endemicity of onchocerciasis in Galim is due to 'natural heterologous vaccination' by the large annual number of O. ochengi-L3, inoculated into man by anthropo-boophilic S. damnosum s.l. The importance of micro-epidemiology for the understanding of the interlinkage of human and animal onchocerciasis is discussed.

Bovine onchocercosis in north Cameroon

Ventral skin biopsies from 204 Gudali cattle of the Vina division in the Adamawa highlands revealed microfilariae of Onchocerca gutturosa, O. ochengi and O. dukei in 85%, 51% and 8% of the animals, respectively. In 60 Fulani cattle from the Tcholliré division in the Sudan savanna, the same microfilaria species were detected in 92%, 83% and 47% of the animals. Onchocerca armillata adult worms were found in 67% of the Gudalis and in 100% of the Fulanis. In areas of high transmission the prevalences declined in old animals, possibly indicating acquired resistance. For all species no significant difference in prevalence was found between male and female cattle. The microfilariae of O. ochengi and O. dukei were concentrated in the skin of the posterior and anterior belly, respectively. Onchocerca gutturosa microfilariae had highest densities on the hump and near the umbilicus, whereas those of O. armillata were distributed more evenly across the body surface. In infected hides the mean microfilarial densities of O. gutturosa, O. ochengi, O. dukei and O. armillata were respectively 3.1 microfilariae (mff) mg-1, 0.6 mff mg-1, 0.7 mff mg-1 and 0.092 mff mg-1 for the whole body surface and 9.3 mff mg-1, 3.8 mff mg-1 and 1.9 mff mg-1 for the sites of highest density (O. armillata had no predilection site). Ninety-five per cent of the microfilariae were located in the uppermost skin layer of 2 mm depth, 5% were in the corium and none were found in the subcutis. Two cattle had skin microfilariae of a hitherto unknown Onchocerca species.

Age-related satisfaction with complete dentures, desire for improvement and attitudes to implant treatment

In the edentulous lower jaw implant stabilised dentures have proved clinically so successful that the indication for this treatment is now being discussed more often with geriatric patients. The aim of this study of edentate subjects was to determine the age-relation of the demand for denture improvement, the risks and feasibility of implant treatment. Sixty four complete denture wearers aged from 42 to 84 years took part in the study. A questionnaire was used to determine the subjective demand for denture improvement. For 33 subjects implants seemed possible. For these patients fear and scepticism concerning implant treatment were specified and quantified. Impaired general health was the most frequent absolute contra-indication for implants; the local oral prerequisites tended to be slightly less favourable in elderly. Older patients were more satisfied with poorly fitting dentures and were less prepared to take trouble to achieve denture improvement. Although scepticism concerning implant treatment was not age-related, patients who were keen for an improvement of their dentures were significantly younger and less sceptical about implants.

A strictly anaerobic nitrate-reducing bacterium growing with resorcinol and other aromatic compounds

With resorcinol as sole source of energy and organic carbon, two stains of gram-negative, nitrate-reducing bacteria were isolated under strictly anaerobic conditions. Strain LuBRes1 was facultatively anaerobic and catalase- and superoxide dismutase-positive. This strain was affiliated with Alcaligenes denitrificans on the basis of substrate utilization spectrum and peritrichous flagellation. Strain LuFRes1 could grow only under anaerobic conditions with oxidized nitrogen compounds as electron acceptor. Cells were catalase-negative but superoxide dismutase-positive. Since this strain was apparently an obligate nitrate reducer, it could not be grouped with any existing genus. Resorcinol was completely oxidized to CO2 by both strains. Neither an enzyme activity reducing or hydrolyzing the resorcinol molecule, nor an acyl-CoA-synthetase activating resorcylic acids or benzoate was detected in cell-free extracts of cells grown with resorcinol. In dense cell suspensions, both strains produced a compound which was identified as 5-oxo-2-hexenoic acid by mass spectrometric analysis. This would indicate a direct, hydrolytic cleavage of the resorcinol nucleus without initial reduction.

Detection of Loa loa-specific DNA in blood from occult-infected individuals

Accurate and specific diagnosis of human loiasis is of crucial importance in an endemic area where two-thirds of infected individuals are without circulating microfilariae (occult loiasis). By using the polymerase chain reaction (PCR) and specific primers to the repeat 3 region (15r3) of the gene coding for Loa loa 15-kDa polyprotein antigen, DNA was amplified from total blood lysate of occult-infected subjects. A 396-bp DNA fragment was specifically detected. We tested the specificity of this method by qualitative hybridization to PCR products using blood lysates of the following subjects: (1) from Gabon (80 individuals residing in L. loa endemic area where loiasis exists sympatrically with Mansonella perstans); (2) from Togo (12 individuals infected with Onchocerca volvulus and M. perstans); (3) from Tahiti (12 individuals infected with Wuchereria bancrofti); and (4) from Mali (12 individuals infected with O. volvulus and M. perstans). Samples from Gabon included 60 L. loa amicrofilaremics and 20 L. loa occult-infected subjects. Qualitative hybridization carried out at 50 degrees C on PCR products, using a 15r3-specific oligonucleotide probe, revealed hybridization with L. loa-infected samples from Gabon and four samples from Togo after 2 days exposure to the film. The positive samples from Togo were characterized by the use of nested PCR. Three nested PCR products have been sequenced. No differences were observed between the three sequences and they are 99.72% identical to L. loa 15r3. None of bancroftian-infected individuals from Tahiti, nor O. volvulus- and M. perstans-infected individuals from Mali reacted after 1 week's exposure (overexposure) to the film. This allows us to conclude first that our 15r3 PCR assay is specific for L. loa and secondly that L. loa infections occur in Togo. The sensitivity of this 15r3 PCR assay was further investigated with occult patients and field-collected amicrofilaremic samples. We found that 19 of the 20 occult-infected individuals were positive on Southern hybridization, whereas 35/60 amicrofilaremics were positive. These results have shown that the sensitivity of this assay in detecting unequivocal, parasitologically proven occult loiasis was 95%, while the specificity with regard to the sympatric M. perstans was 100%.

T helper responsiveness in human Loa loa infection; defective specific proliferation and cytokine production by CD4+ T cells from microfilaraemic subjects compared with amicrofilaraemics

The proliferation and cytokine profiles of peripheral blood mononuclear cells (PBMC) from microfilaraemic (Mf+) subjects infected by Loa loa in response to antigens of several parasitic stages were compared with those from amicrofilaraemic (Mf-) individuals. While a strong lymphoproliferative response and consistent levels of both Th1 (IL-2, interferon-gamma (IFN-gamma)) and Th2 (IL-4, IL-5) type cytokines were observed in response to adult worm (AW) and microfilariae (Mf) antigen in Mf- individuals, Mf+ subjects were characterized by a T cell unresponsiveness, including proliferation, cytokine production and IL-2 mRNA expression. Conversely, T cell responsiveness to mitogens and non-specific antigen were similar in the two endemic populations. Depletion of lymphocyte subpopulations indicated that T CD4+ were mainly involved in the specific cellular response. In contrast to other cytokines, IL-10 was produced in response to all parasitic stages, in both Mf+ and Mf- patients. Neutralization of IL-10 did not restore cytokine production in Mf+ patients, while B7 mRNA expression was similar between Mf+ and Mf- subjects in response to Mf antigen, suggesting that IL-10 was not the only factor responsible for T cell unresponsiveness. Mf+ patients have lower Mf antigen-specific IgG levels compared with Mf-, and there is a significant correlation between Mf antigen-specific antibodies and IL-5 responses. These findings suggest that Mf- status is correlated with T helper responsiveness, including proliferation and production of both Th1- and Th2-type cytokines, whereas Mf+ status is characterized by unresponsiveness of the same cell population, induced and/or maintained by microfilariae.

Effect of cold plasma on periodontal wound healing-an in vitro study

OBJECTIVES

Cold atmospheric plasma (CAP), a room temperate ionized gas, seems to be a possible way to enhance tissue recovery. An in vitro study was conducted to investigate the influence of medical CAP on the regenerative capacity of human periodontal ligament (PDL) cells.

MATERIAL AND METHODS

Human PDL cells were subjected to CAP at various intensities, distances, and durations. The effects of CAP on a number of specific markers were studied at transcriptional level using real-time PCR. Additionally, an in vitro wound healing assay was applied to PDL cell monolayers either in the presence or absence of CAP by using JuLI™ Br Live Cell Analyzer and software. Finally, cell viability of CAP-treated cells was analyzed by an XTT assay.

RESULTS

CAP treatment enhanced significantly the expression of the cytokines tumor necrosis factor (TNF)α, cyclooxygenase (COX)2, interleukin (IL)-1β, IL-6, IL-8, collagen (COL)1α, and matrix metalloproteinase (MMP)1, as well as the proliferation markers Ki67 and proliferating cell nuclear antigen (PCNA), but downregulated apoptotic markers Apaf1 and p53. Additionally, the in vitro wound healing rate was significantly enhanced after CAP application. Moreover, CAP treatment resulted in a significantly increased cell viability in the XTT assay.

CONCLUSION

This in vitro study shows that CAP has regulatable effects on markers of periodontal wound healing thereby underlining the potential use of CAP as a benefit treatment strategy.

CLINICAL RELEVANCE

Our study demonstrates the application of CAP in the treatment of oral pathologies suggesting a promising future treatment approach.

Blunt-end and single-strand ligations by Escherichia coli ligase: influence on an in vitro amplification scheme

A ligase-based, in vitro DNA amplification system (LAR) has been described by Wu and Wallace [Genomics 4 (1989) 560-569]. This strategy is based on the ability of a DNA ligase to join the 5' phosphate of one DNA molecule to the 3' hydroxyl of a second during a nick-closing reaction. Escherichia coli DNA ligase has been used in place of the T4 DNA ligase in our study in order to limit template-independent ligation activities, which lower the sensitivity of this amplification procedure. The results of this study indicate that E. coli ligase also joins blunt-ended DNA molecules and some single-stranded oligodeoxyribonucleotides, in the absence of a complementary template, with an efficiency which is sensitive to both the concentrations of DNA substrate and enzyme.

Occupational exposure to inhalable and total aerosol in the primary nickel production industry

OBJECTIVES

This paper describes a study that was carried out in the primary nickel production industry to investigate the levels of personal exposure to aerosols containing nickel and the impact on exposure assessment of introducing new personal sampling techniques with performance consistent with the latest particle size-selective criteria.

METHODS

Experiments were carried out at workplaces in mining, milling, smelting, and refining works to investigate the effect of changing from the current method of total aerosol (with the widely used 37 mm filter holder) to the new method of measuring inhalable aerosol (with the Institute of Occupational Medicine (IOM) inhalable aerosol sampler).

RESULTS

The results show that inhalable aerosol exposure concentrations--for both overall aerosol and for total nickel--were consistently and significantly higher than the corresponding total aerosol concentrations. Weighted least squares linear regression yielded IOM/37 mm factors ranging from about 1.2 to 4.0. The exposure data for each company process were found to be log-normally distributed.

CONCLUSIONS

The results suggest the possibility of generating a single pragmatic factor for each company process for converting current total aerosol exposures to new exposures based on the inhalability concept contained in the latest particle size-selective criteria for aerosol exposure assessment. Such data may be important in determining new occupational exposure limits for nickel.

Impact of PET/CT for Assessing Response to Immunotherapy-A Clinical Perspective

Cancer immunotherapy using immune-checkpoint inhibitors (ICI) has revolutionized the therapeutic landscape of various malignancies like non-small-cell lung cancer or melanoma. Pre-therapy response prediction and assessment during ICI treatment is challenging due to the lack of reliable biomarkers and the possibility of atypical radiological response patterns. Positron emission tomography/computed tomography (PET/CT) enables the visualization and quantification of metabolic lesion activity additional to conventional CT imaging. Various biomarkers derived from PET/CT have been reported as predictors for response to ICI and may aid to overcome the challenges clinicians currently face in the management of ICI-treated patients. In this narrative review, experts in nuclear medicine, thoracic oncology, dermatooncology, hemato- and internal oncology, urological and head/neck tumors performed literature reviews in their respective field and a joint discussion on the use of PET/CT in the context of ICI treatment. The aims were to give a clinical overview on present standards and evidence, to identify current challenges and fields of research and to enable an outlook to future developments and their possible implications. Multiple promising studies concerning ICI response assessment or prediction using biomarkers derived from PET/CT alone or as composite biomarkers have been identified for various malignancies and disease stages. Of interest, additional major incentives in the field may evolve from novel tracers specifically targeting immune-checkpoint molecules which could allow not only response assessment and prognosis, but also visualization of histological tumor cell properties like programmed death-ligand (PD-L1) expression in vivo. Despite the broad range of existing literature on PET/CT-derived biomarkers in ICI therapy, implications for daily clinical practice remain elusive. High-quality prospective data are urgently warranted to determine whether patients benefit from the application of PET/CT in terms of prognosis. At the moment, the lack of such evidence as well as the absence of standardized imaging methods and biomarkers still precludes PET/CT imaging to be included in the relevant clinical practice guidelines.

Age-related differences in parasitosis may indicate acquired immunity against microfilariae in cattle naturally infected with Onchocerca ochengi

Onchocerca ochengi is a common parasite of cattle in savanna areas of West Africa and its adult stages inhabit intradermal nodules. We have exploited the accessibility of the macrofilariae to examine quantitative and qualitative differences in both the macro- and microfilariae (mff) in relation to age in naturally infected cattle. Autochthonous cattle at a site on the Adamawa plateau, North Cameroon, situated near a perennial Simulium damnosum s.l. breeding site, were examined in three age groups (1.5-2.5, n = 34; 3-5, n = 39 and greater than or equal to 8 years old, n = 21). Skin mff densities were assessed from ventral skin biopsies, total body counts of nodules were done by palpation and 1-4 nodules were excised from positive animals, collagenase digested and the numbers and condition of macrofilariae determined. Embryogenesis profiles (embryograms) were done on a representative number of female worms in each age group. The overall prevalence of infection in the study population was 71% for mff and 85% for nodules. Nodule prevalence increased significantly from the 1.5-2.5 to 3-5 years old groups, but no other inter-age prevalences were significantly different. While the mean number of nodules per animal increased with age, geometric means (gm) 3.7, 15.5 and 23.1, the skin mff density maximized in the middle age group and decreased significantly in the old animals (gm 15.8, 44.7 and 11.4 mff/g, difference between latter two parameters significant, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Hippuric acid and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid in serum and urine. Analytical approaches and clinical relevance in kidney diseases

Hippuric acid (HA) and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (FA) were determined in serum, plasma, ultrafiltrate and urine by gas chromatography (GC), high-performance liquid chromatography and GC with mass-selective detection, and the methods were compared. As determined by affinity chromatography and analysis of serum and ultrafiltrate, 0.5% of FA in serum occurs free and 99.5% is bound to albumin. In haemodialysed patients with chronic renal failure, the plasma levels of HA and FA are elevated in comparison with normal controls and hospital patients without kidney diseases: HA, 11.1 +/- 5.7 mg/dl (n = 86); FA, 1.9 +/- 1.2 mg/dl (n = 86). Gradual increases in HA in serum, depending on the creatinine concentrations, are found in non-dialysed patients with chronic renal failure. By haemodialysis and haemofiltration the HA levels are lowered (53-66 and 30-36%, respectively), whereas FA is not dialysable.

Human occult loiasis: field evaluation of a nested polymerase chain reaction assay for the detection of occult infection

A nested polymerase chain reaction (nested PCR) assay, targeted on the repeat 3 region (15r3) of the gene coding for a Loa loa 15 kD polyprotein, was developed to detect L. loa infection. The assay has a sensitivity of 95% and is 100% specific with regard to sympatric filarial parasites: Mansonella perstans, Onchocerca volvulus and Wuchereria bancrofti. In this field study in a mixed filarial (L. loa and M. perstans) endemic region of Gabon, 157 L. loa amicrofilaraemic blood samples (AMF; diagnosed by leucoconcentration followed by standard microscopic examination) from the residents from four villages were screened by the 15r3-nested PCR assay. The assay detected 106 occult infected subjects among the 157 AMF individuals (68%), including 59 of 87 adults (68%) and 47 of 70 children (67%). In each village the prevalence of occult infection was, respectively, 38%, 52%, 79% and 80% for Moyabi, Djoutou, N'djokaye and Okoumbi. The annual transmission potential (ATP) of loiasis has been estimated to be 250 infective larvae (L 3) per man per year for Moyabi and Djoutou, 1800 for N'djokaye and 433000 L3/man/year for Okoumbi. This implies a correlation between occult infection of loiasis and the intensity of transmission. By contrast, the prevalence of L. loa microfilariae was 21% for Okoumbi, 22%, for N'djokaye and 19% for Djoutou and Moyabi. These results show that the prevalence of loiasis in this region of Gabon is higher than previously described by standard microscopic examination and that the application of this assay will be significant in the development of control strategies for loiasis.

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.

Onchocerca ochengi: assessment of the Simulium vectors in north Cameroon

In the savanna areas of tropical Africa, cattle are frequently infected with the filaria Onchocerca ochengi. This parasite is closely related to Onchocerca volvulus, the causative agent of human onchocerciasis (river blindness), and is capable of developing in the same vector, Simulium damnosum s.l. In North Cameroon, where both O. ochengi and O. volvulus are endemic, we carried out a field study (reported in this and 2 following papers) to examine to which extent the transmission of the 2 parasite species overlap and what influence this has on the epidemiology of human onchocerciasis. In this paper we report our experiments to determine which of the S. damnosum species in North Cameroon act as vectors of O. ochengi, how efficiently they do so and whether other Simulium species play a vector role. To this end, infected cattle were exposed near 5 rivers in different geographical areas. Among 14 Simulium species identified as aquatic and/or adult stages at these rivers, only 6 (S. squamosum, S. damnosum s.s., S. sirbanum, S. bovis, S. wellmanni and S. hargreavesi) were found to bite cattle in important numbers in at least 1 of the sites. The 3 species of the S. damnosum complex were all capable of ingesting microfilariae (mf) of O. ochengi and developing a proportion of them to infective larvae (L3). Whereas S. squamosum and S. damnosum s.s., the prevailing vectors in the Guinea and Sudan savanna respectively, showed a high vector competence (17% of ingested mf developed to L3), S. sirbanum, which was much rarer in both areas, appeared to have a much lower susceptibility (2%). Other boophilic Simulium species were only seen in certain sites and seasons, being either incapable of ingesting important numbers of O. ochengi mf from body regions where these mf were abundant (S. bovis, S. hargreavesi); not able to support the development of ingested mf to L3 (S. wellmanni), or bit cattle preferentially in the ears, where O. ochengi mf do not occur (S. hargreavesi). We conclude that in North Cameroon members of the S. damnosum complex are the only important vectors of O. ochengi, with S. squamosum and S. damnosum s.s. being the main vectors.

The development of Onchocerca dukei and O. ochengi microfilariae to infective-stage larvae in Simulium damnosum s.l. and in members of the S. medusaeforme group, following intra-thoracic injection

Neonate Simulium females from an endemic area of human and bovine onchocerciasis in North-Cameroon were injected in one set of experiments with microfilariae (mff) of Onchocerca dukei and in another with mff of O. ochengi. Onchocerca dukei was found to develop to infective third-stage larvae in Simulium flies: 148 third-stage larvae (28.1% of injected mff) were recovered in S. hargreavesi, seven (10.4% of injected mff) in S. vorax, and 12 (1.3%) in S. damnosum s.l. Onchocerca ochengi mff developed in S. hargreavesi at a rate of 17.3% and in S. damnosum s.l. at 16.1%, yielding a total of 77 and 32 third-stage larvae respectively. Onchocerca dukei infective larvae had a mean length of 717.3 microns and a mean maximum diameter of 17.5 microns, and were slightly shorter and conspicuously thinner than those of O. ochengi (748.3 microns x 20.4 microns). All larval stages of O. dukei typically had an attenuated anterior end. The implications of these findings for the epidemiology of human onchocerciasis are discussed.

Distribution of microfilariae of Onchocerca lienalis and Onchocerca gutturosa in the skin of cattle in Germany and their development in Simulium ornatum and Culicoides nubeculosus following artificial infestation

Onchocerca microfilariae were isolated form the umbilicus and neck of 438 cow hides at the abattoir in Tübingen, F.R.G. The overall Onchocerca infection rate was 40.4%. The presence of Onchocerca lienalis and O. gutturosa microfilariae, which are difficult to distinguish by morphological criteria, was retrospectively demonstrated after artifically infesting Simulium ornatum and Culicoides nubeculosus and identifying the infective larvae recovered. Nine of 16 samples of umbilical microfilariae fed to C. nubeculosus through a latex membrane developed to O. gutturosa third stage larvae (L3). Six of seven umbilical samples injected into the thorax of S. ornatum yielded O. lienalis L3. In six infestation trials in which microfilariae were introduced both into S. ornatum and C. nubeculosus, O. lienalis L3 were recovered exclusively from simuliids, while O. gutturosa L3 developed only in midges. Of six umbilical skins tested by cross-infestation, one contained exclusively O. gutturosa microfilariae, four only O. lienalis microfilariae and one was infected with both species. Developmental success of O. lienalis microfilariae to L3 in S. ornatum following intrathoracic injection was 22% of the mean inoculum. O. gutturosa microfilariae, ingested by C. nubeculosus through a latex membrane, developed to L3 at a rate of 2.3% of the mean microfilarial uptake.