Inflammatory status and preerythrocytic stages of malaria: role of the C-reactive protein

C-Reactive Protein: Friend or Foe? Phylogeny From Heavy Metals to Modified Lipoproteins and SARS-CoV-2

Animal C-reactive protein (CRP) has a widespread existence throughout phylogeny implying that these proteins have essential functions mandatory to be preserved. About 500 million years of evolution teach us that there is a continuous interplay between emerging antigens and components of innate immunity. The most archaic physiological roles of CRP seem to be detoxication of heavy metals and other chemicals followed or accompanied by an acute phase response and host defense against bacterial, viral as well as parasitic infection. On the other hand, unusual antigens have emerged questioning the black-and-white perception of CRP as being invariably beneficial. Such antigens came along either as autoantigens like excessive tissue-stranded modified lipoprotein due to misdirected food intake linking CRP with atherosclerosis with an as yet open net effect, or as foreign antigens like SARS-CoV-2 inducing an uncontrolled CRP-mediated autoimmune response. The latter two examples impressingly demonstrate that a component of ancient immunity like CRP should not be considered under identical “beneficial” auspices throughout phylogeny but might effect quite the reverse as well.

Identification of protein markers in patients infected with Plasmodium knowlesi, Plasmodium falciparum and Plasmodium vivax

Malaria is caused by parasitic protozoans of the genus Plasmodium and is one of the most prevalent infectious diseases in tropical and subtropical regions. For this reason, effective and practical diagnostic methods are urgently needed to control the spread of malaria. The aim of the current study was to identify a panel of new malarial markers, which could be used to diagnose patients infected with various Plasmodium species, including P. knowlesi, P. vivax and P. falciparum. Sera from malaria-infected patients were pooled and compared to control sera obtained from healthy individuals using the isobaric tags for relative and absolute quantitation (iTRAQ) technique. Mass spectrometry was used to identify serum proteins and quantify their relative abundance. We found that the levels of several proteins were increased in pooled serum from infected patients, including cell adhesion molecule-4 and C-reactive protein. In contrast, the serum concentration of haptoglobin was reduced in malaria-infected individuals, which we verified by western blot assay. Therefore, these proteins might represent infectious markers of malaria, which could be used to develop novel diagnostic tools for detecting P. knowlesi, P. vivax and P. falciparum. However, these potential malarial markers will need to be validated in a larger population of infected individuals.

Affinity proteomics reveals elevated muscle proteins in plasma of children with cerebral malaria

Systemic inflammation and sequestration of parasitized erythrocytes are central processes in the pathophysiology of severe Plasmodium falciparum childhood malaria. However, it is still not understood why some children are more at risks to develop malaria complications than others. To identify human proteins in plasma related to childhood malaria syndromes, multiplex antibody suspension bead arrays were employed. Out of the 1,015 proteins analyzed in plasma from more than 700 children, 41 differed between malaria infected children and community controls, whereas 13 discriminated uncomplicated malaria from severe malaria syndromes. Markers of oxidative stress were found related to severe malaria anemia while markers of endothelial activation, platelet adhesion and muscular damage were identified in relation to children with cerebral malaria. These findings suggest the presence of generalized vascular inflammation, vascular wall modulations, activation of endothelium and unbalanced glucose metabolism in severe malaria. The increased levels of specific muscle proteins in plasma implicate potential muscle damage and microvasculature lesions during the course of cerebral malaria.

Why do some malaria-infected children develop severe and lethal forms of the disease, while others only have mild forms? In order to try to find potential answers or clues to this question, we have here analyzed more than 1,000 different human proteins in the blood of more than 500 malaria-infected children from Ibadan in Nigeria, a holoendemic malaria region. We identified several proteins that were present at higher levels in the blood from the children that developed severe malaria in comparison to those that did not. Some of the most interesting identified proteins were muscle specific proteins, which indicate that damaged muscles could be a discriminatory pathologic event in cerebral malaria compared to other malaria cases. These findings will hopefully lead to an increased understanding of the disease and may contribute to the development of clinical algorithms that could predict which children are more at risks to severe malaria. This in turn will be of high value in the management of these children in already overloaded tertiary-care health facilities in urban large densely-populated sub-Saharan cities with holoendemic malaria such as in the case of Ibadan and Lagos.

Natural acquisition of immunity to Plasmodium vivax: epidemiological observations and potential targets

Population studies show that individuals acquire immunity to Plasmodium vivax more quickly than Plasmodium falciparum irrespective of overall transmission intensity, resulting in the peak burden of P. vivax malaria in younger age groups. Similarly, actively induced P. vivax infections in malaria therapy patients resulted in faster and generally more strain-transcending acquisition of immunity than P. falciparum infections. The mechanisms behind the more rapid acquisition of immunity to P. vivax are poorly understood. Natural acquired immune responses to P. vivax target both pre-erythrocytic and blood-stage antigens and include humoral and cellular components. To date, only a few studies have investigated the association of these immune responses with protection, with most studies focussing on a few merozoite antigens (such as the Pv Duffy binding protein (PvDBP), the Pv reticulocyte binding proteins (PvRBPs), or the Pv merozoite surface proteins (PvMSP1, 3 & 9)) or the circumsporozoite protein (PvCSP). Naturally acquired transmission-blocking (TB) immunity (TBI) was also found in several populations. Although limited, these data support the premise that developing a multi-stage P. vivax vaccine may be feasible and is worth pursuing.

Inhibitory effect of TNF-α on malaria pre-erythrocytic stage development: influence of host hepatocyte/parasite combinations

Background

The liver stages of malaria parasites are inhibited by cytokines such as interferon-γ or Interleukin (IL)-6. Binding of these cytokines to their receptors at the surface of the infected hepatocytes leads to the production of nitric oxide (NO) and radical oxygen intermediates (ROI), which kill hepatic parasites. However, conflicting results were obtained with TNF-α possibly because of differences in the models used. We have reassessed the role of TNF-α in the different cellular systems used to study the Plasmodium pre-erythrocytic stages.

Methods and Findings

Human or mouse TNF-α were tested against human and rodent malaria parasites grown in vitro in human or rodent primary hepatocytes, or in hepatoma cell lines. Our data demonstrated that TNF-α treatment prevents the development of malaria pre-erythrocytic stages. This inhibitory effect however varies with the infecting parasite species and with the nature and origin of the cytokine and hepatocytes. Inhibition was only observed for all parasite species tested when hepatocytes were pre-incubated 24 or 48 hrs before infection and activity was directed only against early hepatic parasite. We further showed that TNF-α inhibition was mediated by a soluble factor present in the supernatant of TNF-α stimulated hepatocytes but it was not related to NO or ROI. Treatment TNF-α prevents the development of human and rodent malaria pre-erythrocytic stages through the activity of a mediator that remains to be identified.

Conclusions

Treatment TNF-α prevents the development of human and rodent malaria pre-erythrocytic stages through the activity of a mediator that remains to be identified. However, the nature of the cytokine-host cell-parasite combination must be carefully considered for extrapolation to the human infection.

Modulating effects of plasma containing anti-malarial antibodies on in vitro anti-malarial drug susceptibility in Plasmodium falciparum

Background

The efficacy of anti-malarial drugs is determined by the level of parasite susceptibility, anti-malarial drug bioavailability and pharmacokinetics, and host factors including immunity. Host immunity improves the in vivo therapeutic efficacy of anti-malarial drugs, but the mechanism and magnitude of this effect has not been characterized. This study characterized the effects of 'immune' plasma to Plasmodium falciparumon the in vitro susceptibility of P. falciparum to anti-malarial drugs.

Methods

Titres of antibodies against blood stage antigens (mainly the ring-infected erythrocyte surface antigen [RESA]) were measured in plasma samples obtained from Thai patients with acute falciparum malaria. 'Immune' plasma was selected and its effects on in vitro parasite growth and multiplication of the Thai P. falciparum laboratory strain TM267 were assessed by light microscopy. The in vitro susceptibility to quinine and artesunate was then determined in the presence and absence of 'immune' plasma using the ³H-hypoxanthine uptake inhibition method. Drug susceptibility was expressed as the concentrations causing 50% and 90% inhibition (IC₅₀ and IC₉₀), of ³H-hypoxanthine uptake.

Results

Incubation with 'immune' plasma reduced parasite maturation and decreased parasite multiplication in a dose dependent manner. ³H-hypoxanthine incorporation after incubation with 'immune' plasma was decreased significantly compared to controls (median [range]; 181.5 [0 to 3,269] cpm versus 1,222.5 [388 to 5,932] cpm) (p= 0.001). As a result 'immune' plasma reduced apparent susceptibility to quinine substantially; median (range) IC₅₀ 6.4 (0.5 to 23.8) ng/ml versus 221.5 (174.4 to 250.4) ng/ml (p = 0.02), and also had a borderline effect on artesunate susceptibility; IC₅₀ 0.2 (0.02 to 0.3) ng/ml versus 0.8 (0.2 to 2.3) ng/ml (p = 0.08). Effects were greatest at low concentrations, changing the shape of the concentration-effect relationship. IC₉₀ values were not significantly affected; median (range) IC₉₀ 448.0 (65 to > 500) ng/ml versus 368.8 (261 to 501) ng/ml for quinine (p > 0.05) and 17.0 (0.1 to 29.5) ng/ml versus 7.6 (2.3 to 19.5) ng/ml for artesunate (p = 0.4).

Conclusions

'Immune' plasma containing anti-malarial antibodies inhibits parasite development and multiplication and increases apparent in vitro anti-malarial drug susceptibility of P. falciparum. The IC₉₀ was much less affected than the IC₅₀ measurement.

Patterns of co-association of C-reactive protein and nitric oxide in malaria in endemic areas of Iran

In addition to numerous immune factors, C-reactive protein (CRP) and nitric oxide (NO) are believed to be molecules of malaria immunopathology. The objective of this study was to detect CRP and NO inductions by agglutination latex test and Griess microassay respectively in both control and malaria groups from endemic areas of Iran, including Southeastern (SE) (Sistan & Balouchestan, Hormozgan, Kerman) and Northwestern (NW) provinces (Ardabil). The results indicated that CRP and NO are produced in all malaria endemic areas of Iran. In addition, more CRP and NO positive cases were observed amongst malaria patients in comparison with those in control group. A variable co-association of CRP/NO production were detected between control and malaria groups, which depended upon the malaria endemic areas and the type of plasmodia infection. The percentage of CRP/NO positive cases was observed to be lower in NW compare to SE region, which may be due to the different type of plasmodium in the NW (Plasmodium vivax) with SE area (P. vivax, Plasmodium falciparum, mixed infection). The fluctuations in CRP/NO induction may be consistent with genetic background of patients. Although, CRP/NO may play important role in malaria, their actual function and interaction in clinical forms of disease remains unclear.

Fcgamma receptor IIA and IIIB polymorphisms are associated with susceptibility to cerebral malaria

Human FcgammaRIIA and FcgammaRIIIB exhibit genetic polymorphisms, FcgammaRIIA-131H/R and FcgammaRIIIB-NA1/NA2, coding for different capacities for IgG binding and phagocytosis. Recently, FcgammaRIIA-131R was reported to be associated with protection against high-density Plasmodium falciparum infection in Kenya. Furthermore, FcgammaRIIIB-NA1/NA2 polymorphism was shown to influence FcgammaRIIA function in an allele-specific manner. In this study, we examined a possible association of FcgammaRIIA-131H/R and FcgammaRIIIB-NA1/NA2 polymorphisms with malaria severity in 107 cerebral malaria patients, 157 non-cerebral severe malaria patients, and 202 mild malaria controls living in northwest Thailand. This study reveals that, with the FcgammaRIIIB-NA2 allele, the FcgammaRIIA-131H/H genotype is associated with susceptibility to cerebral malaria (OR 1.85, 95% CI 1.14-3.01; P=0.012), although these polymorphisms are not individually involved in the disease severity. Our results suggest that FcgammaRIIA-131H/R and FcgammaRIIIB-NA1/NA2 polymorphisms have an interactive effect on host defense against malaria infection.

Host responses to Plasmodium yoelii hepatic stages: a paradigm in host-parasite interaction

The liver stage of malaria, caused by the genus Plasmodium, is clinically silent, but immunologically significant. Ample evidence exists for an effective CD8(+) T cell response to this stage as well as the involvement of gammadeltaT cells and NK1.1(int) cells in immunized animal models. In contrast, there is little information concerning responses in a naive host. Here we report that several host gene expressions in the liver, spleen, and kidney of BALB/c mice are altered during the liver stage of Plasmodium yoelii infection. Really interesting new gene 3 (Ring3), semaphorin subclass 4 member G, glutamylcysteine synthetase, and p45 NF erythroid 2 were all up-regulated 24 h after infection with P. yoelii. Semaphorin subclass 4 member G expression was elevated in the kidney, whereas Ring3 was elevated in both spleen and kidney. The expression of TNF-alpha (TNF-alpha and IFN-gamma) were down-regulated in all three tissues tested except in infected spleen where IFN-gamma was elevated. P. yoelii-related host gene changes were compared with those in Toxoplasma gondii-infected livers. Ring3 expression increased 5-fold over control values, whereas expression of the other transcripts remained unchanged. TNF-alpha and IFN-gamma expressions were increased in the Toxoplasma-infected livers. The uniform increase of Ring3 expression in both Plasmodium- and Toxoplasma-infected livers suggests an innate immune response against parasitic infections, whereas the other gene expression changes are consistent with Plasmodium parasite-specific responses. Taken together, these changes suggest the immune responses to P. yoelii infection are both parasite and organ specific.

Experimental erythrocytic malaria infection induces elevated serum amyloid P production in mice

Experimental blood-stage malaria infection of NIH mice was observed to induce an acute phase response (APR). Infection of mice with either P. chabaudi, P. vinckei (both non-lethal) or P. berghei (lethal infection) resulted in elevated serum amyloid P (SAP) production, the major acute phase protein in mice. Peak production occurred at the peak of the parasitaemia (approximately day 10 post infection). SAP isolated from the serum of P. chabaudi infected mice was shown to inhibit the growth of intra-erythrocytic malaria parasites in vitro. Furthermore, isolated SAP suppressed the proliferative response of splenocytes taken from a naïve mouse to concanavalin A. To assess if SAP had a protective role in vivo during experimental blood-stage infection, IL-6 deficient mice, which have a significantly reduced APR, were infected with P. chabaudi. A significant extension to the primary parasitaemia was observed in IL-6 deficient mice compared to infected wild type mice. These observations demonstrate that blood-stage malaria infection induces a systemic APR and that this may contribute to the immune response to infection in an anti-parasitic or immunomodulatory manner.

Rouleaux-forming serum proteins are involved in the rosetting of Plasmodium falciparum-infected erythrocytes

Excessive sequestration of Plasmodium falciparum-infected (pRBC) and uninfected erythrocytes (RBC) in the microvasculature, cytoadherence, and rosetting, have been suggested to be correlated with the development of cerebral malaria. P. falciparum erythrocyte membrane protein-1 (PfEMP1) is the parasite-derived adhesin which mediates rosetting. Herein we show that serum proteins are crucial for the rosette formation of four strains of parasites (FCR3S1, TM284, TM180, and R29), whereas the rosettes of a fifth strain (DD2) are serum independent. Some parasites, e.g., FCR3S1, can be depleted of all rosettes by washes in heparin and Na citrate and none of the rosettes remain when the parasite is grown in foetal calf serum or ALBUMAX. Rosettes of other parasites are less sensitive; e.g., 20% of TM180 and R29 and 70% of TM284 rosettes still prevail after cultivation. A serum fraction generated by ion-exchange chromatography and poly-ethylene-glycol precipitation restored 50% of FCR3S1 and approx 40 to 100% of TM180 rosettes. In FCR3S1, antibodies to fibrinogen reverted the effect of the serum fraction and stained fibrinogen bound to the pRBC surface in transmission electron microscopy. Normal, nonimmune IgM and/or IgG was also found attached to the pRBC of the four serum-dependent strains as seen by surface immunofluorescens. Our results suggest that serum proteins, known to participate in rouleaux formation of normal erythrocytes, produce stable rosettes in conjunction with the recently identified parasite-derived rosetting ligand PfEMP1.

Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan

The haptoglobin phenotypes of Sudanese patients with complicated and uncomplicated falciparum malaria, and those of uninfected randomly selected individuals, were determined by electrophoresis of sera on polyacrylamide gels followed by benzidine staining of the gels. Among 273 malaria patients, the proportions with haptoglobin phenotypes (1-1), (2-1) and (2-2) were 60.8%, 29.7% and 9.5%, respectively, and in 72 cerebral malaria patients the proportions were 63.9%, 29.2%, and 6.9%. The distribution among 208 control individuals was 26.0%, 55.8% and 18.3%, respectively. The difference between patients and controls was highly significant (P < 0.001). The distribution of the different haptoglobin phenotypes among the randomly selected group of 208 Sudanese individuals was comparable to that in many other populations. The results suggests that the haptoglobin phenotype (1-1) is associated with susceptibility to falciparum malaria and the development of severe complications; alternatively, the other phenotypes may confer resistance.

A method for the quantitative assessment of malaria parasite development in organs of the mammalian host

A non-radioactive PCR method was developed to quantify the development of malaria parasites in the infected host. This was achieved by using Plasmodium genus-specific primers corresponding to the parasite's small subunit ribosomal RNA genes. The quantification of the PCR product was performed by high performance liquid chromatography, and calibration curves were obtained by amplification from defined quantities of purified Plasmodium genomic DNA. Using this method, it was possible to quantify development of P. berghei and P. yoelii blood-stage parasites from blood and brain samples of infected mice, and of hepatic stage parasites, from liver samples of mice infected with different numbers of sporozoites.

Iron overload increases hepatic development of Plasmodium yoelii in mice

Iron overload in BALB/c mice by treatment with ferric ammonium citrate promotes the hepatic development of Plasmodium yoelii in vivo and in vitro. This was the result of increased penetration of the parasite into hepatocytes since no effect was observed on parasite transformation or maturation. These results could explain why in endemic regions iron supplementation led, in certain studies, to an increase in clinical episodes of malaria and in the prevalence of malaria infection.

Susceptibility to Plasmodium berghei infection in rats is modulated by the acute phase response

Brown Norway (BN) and Sprague Dawley (SD) rats are known to differ in their susceptibility to infection with sporozoites of Plasmodium berghei, as measured by the density of liver schizonts. Because of the known inhibitory effect of non-specific immunomodulators on schizont development, we compared some aspects of the acute phase response in these two rat strains. LPS induced IL-6 production was measured in supernatants of spleen cells and peritoneal macrophages of both strains. SD rats, which are the least susceptible to P. berghei sporozoites, showed significantly higher IL-6 production by macrophages from both sources. When LPS was administered in vivo, SD rats also had a significantly higher IL-6 response. Hepatocytes from both strains were cultured in the presence of IL-6. After three days of culture, alpha 2-Macroglobulin concentrations in the supernatants of SD hepatocytes were much higher than those from BN rats. Kupffer cell depletion in both BN and SD rats was correlated with a significant increase in liver schizont density, but did not abrogate the difference in susceptibility. From these results we conclude that the higher cytokine production capacity of SD rats compared to BN rats, may contribute to the difference in susceptibility to P. berghei sporozoites between these strains, but that other yet unknown factors are also involved.

Nitric oxide-mediated antiplasmodial activity in human and murine hepatocytes induced by gamma interferon and the parasite itself: enhancement by exogenous tetrahydrobiopterin

Expression of inducible nitric oxide (NO) synthase has been shown to inhibit the development of several pathogens, including fungi, bacteria, parasites, and viruses. However, there is still controversy as to whether this effector mechanism can inhibit the development of human pathogens. We now report that gamma interferon (IFN-gamma) induces the elimination of Plasmodium falciparum-infected primary human hepatocytes from cultures and that the antimalarial activity is dependent on NO. Infection with the parasite alone in the absence of added IFN-gamma caused a 10-fold increase in NO formation. Both spontaneous inhibition and IFN-gamma-induced inhibition of Plasmodium yoelii-infected murine hepatocytes were increased with the addition of the NO synthase cofactor tetrahydrobiopterin, or sepiapterin, which is converted to tetrahydrobiopterin. These results indicate that under in vitro conditions the parasite itself provides a signal that triggers induction of the NO pathway in human and murine hepatocytes and that NO formation in infected hepatocytes is limited by tetrahydrobiopterin availability.

In vivo induction of the nitric oxide pathway in hepatocytes after injection with irradiated malaria sporozoites, malaria blood parasites or adjuvants

The mechanisms responsible for malarial immunity induced by repetitive injections of X-irradiated sporozoites have not been fully established. We demonstrate here that a single injection of irradiated sporozoites induced, as soon as 24 h after, a non-permissive state to hepatocyte reinfection with sporozoites in vitro. The same effect was observed when malarial blood forms, irradiated promastigotes of Leishmania infantum, adjuvants (muramyl dipeptide, poly acidylic uridylic) or interferon-gamma was injected. Activation of the nitric oxide (NO) pathway in the hepatocyte by these factors was found to be responsible for hepatocyte refractory status. Additionally, this metabolic pathway is involved in protection given by repeated injections of irradiated sporozoites since protection could be reversed by treating mice at the time of sporozoite challenge with a competitive inhibitor (NG-monomethyl-L-arginine) of the NO pathway. These results suggest that, in view of an antisporozoite vaccine, further studies are needed to find out how to activate specifically a long-lasting nonspecific immune response.

Transgenic mice expressing C-reactive protein are susceptible to infection with Plasmodium yoelii sporozoites

Human and rat C-reactive proteins, major acute-phase reactants, bind to sporozoites and inhibit their in vitro development in hepatocytes (A. Nussler, S. Pied, M. Pontet, F. Miltgen, L. Renia, M. Gentilini, and D. Mazier, Exp. Parasitol. 72:1-7, 1991, and S. Pied, A. Nussler, M. Pontet, F. Miltgen, H. Matile, P.-H. Lambert, and D. Mazier, Infect. Immun. 57:278-282, 1989). We show here that rabbit C-reactive protein has identical properties. Nevertheless, infection by Plasmodium yoelii sporozoites was not prevented in transgenic mice engineered to express rabbit C-reactive protein following induction of gluconeogenesis.

Cytokines inhibit the development of liver schizonts of the malaria parasite Plasmodium berghei in vivo

The effect of induction of an acute-phase response and its mediators on the development of liver schizonts of the rodent malaria parasite Plasmodium berghei was investigated in Brown Norway rats. Subcutaneous injection of turpentine oil 24 h or 5 min before inoculation of sporozoites resulted in 80% and 35% reduction of schizont development, respectively. Turpentine oil induced high plasma levels of interleukin-6 (IL-6). Intraperitoneal administration of IL-1, IL-6 or both, significantly reduced liver schizont development. This reduction was also present if IL-6 had been administered 24 h after sporozoite inoculation. Inhibition induced by IL-1 could be prevented by simultaneous administration of polyclonal anti-IL-6. Administration of polyclonal anti-IL-6 without IL-1 resulted in a 40% increase of liver schizonts compared to control animals. We conclude that induction of an acute-phase response during experimental Plasmodium berghei infections in Brown Norway rats, strongly inhibits liver schizont development and that IL-6 is a key mediator in this process.

Serum cytokine profiles in experimental human malaria. Relationship to protection and disease course after challenge

Serum cytokine profiles were evaluated in immunized and nonimmunized human volunteers after challenge with infectious Plasmodium falciparum sporozoites. Three volunteers had been immunized with x-irradiated sporozoites and were fully protected from infection. Four nonimmune volunteers all developed symptomatic infection at which time they were treated. Sera from all volunteers were collected at approximately 20 time points during the 28-d challenge period; levels of IL-1 alpha, IL-1 beta, IL-2, IFN-gamma, tumor necrosis factor-alpha, IL-4, IL-6, granulocyte macrophage-colony-stimulating factor, and soluble CD4, CD8, and IL-2 receptor (sCD4, sCD8, and sIL-2R, respectively) were determined by ELISA. C-reactive protein (CRP) was assayed by radial immunodiffusion. Parasitemic subjects developed increases in CRP and IFN-gamma, with less marked increases in sIL-2R and sCD8; the other cytokines tested did not change. CRP increases were abrupt and occurred at the onset of fever (day 14 after challenge). IFN-gamma increases were also abrupt, preceding those of fever and CRP by one day. Increases in sIL-2R and sCD8 were more gradual. Increases in fever, CRP, IFN-gamma, and sCD8 were concordant in each volunteer. Early IL-6 increases were noted in the protected vaccinees. Thus, after challenge with virulent P. falciparum, unique systemic cytokine profiles were detectable both in immunized, nonparasitemic volunteers and in unvaccinated, parasitemic subjects. The contrasting cytokine profiles in the two groups may relate to mechanisms of protection and immunopathology in experimental human malaria.

Immunomodulatory agents in the laboratory and clinic

This paper reviews naturally occurring and synthetic compounds that either enhance immune defences or lower both natural and acquired immunity. Immunomodulatory agents used both for laboratory study and clinically for the management of immunologically based diseases are considered.

In vitro activity of CD4+ and CD8+ T lymphocytes from mice immunized with a synthetic malaria peptide

In previous work, a T-helper epitope was mapped within the circumsporozoite protein of the murine malaria parasite Plasmodium yoelii. A 21-mer synthetic peptide corresponding to this epitope (amino acid positions 59-79; referred to as Py1) induced a specific T-cell proliferation in BALB/c and C57BL/6 mice and provided help for the production of antibodies to peptides from the repetitive region, (Gln-Gly-Pro-Gly-Ala-Pro)n, of the P. yoelii circumsporozoite protein when mice were immunized with the Py1 peptide conjugated to the repetitive peptide. Experiments were then designed to study the in vitro antiparasite efficacy of T cells elicited in vivo by peptide immunization. T-cell activity was evaluated on cultured hepatic stages of P. yoelii. Peptide immunizations led to the preferential activation of CD8+ T cells in BALB/c mice and of both CD4+ and CD8+ T cells in C57BL/6 mice. Parasite elimination was mediated directly by these cells and did not seem to be dependent on lymphokine secretion. These data suggest that peptide-primed CD4+ T cells as well as CD8+ T cells could be cytolytic for the hepatic phase of malaria parasites. The fact that the same peptide could activate different lymphocyte populations, depending on the strain of mouse, highlights the importance of a better understanding of the fine mechanisms behind the immune responses to synthetic peptides being tested for malaria vaccine development.