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.     

Endogenous Interleukin-12 Is Not Required for Resolution of Chlamydophila abortus (Chlamydia psittaci Serotype 1) Infection in Mice

A Th1 immune response involving gamma interferon (IFN-gamma) production is required to eliminate Chlamydophila abortus infections. In this study, the role of interleukin-12 (IL-12) in protecting against C. abortus infection was investigated using IL-12(-/-) and wild-type (WT) C57BL/6 mice to determine the role of this Th1-promoting cytokine. IL-12(-/-) mice were able to eliminate the C. abortus infection in a primary infection. However, there was a delay in the clearance of bacteria when IL-12(-/-) mice were infected with a sublethal dose of C. abortus, the delay being associated with a lower production of IFN-gamma. The low level of IFN-gamma was essential for survival of IL-12(-/-) infected mice. Both WT and IL-12(-/-) mice developed a Th1 immune response against C. abortus infection, since they both produced IFN-gamma and immunoglobulin G2a antibody isotype. In addition, when mice were given a secondary infectious challenge with C. abortus, a protective host response which resolved the secondary infection was developed by both WT and IL-12(-/-) mice. The lack of IL-12 resulted in few infiltrating CD4(+) T cells in the liver relative to the number in WT mice, although the number of CD8(+) T cells was slightly higher. The more intense Th1 response presented by WT mice may have a pathogenic effect, as the animals showed higher morbidity after the infection. In conclusion, these results suggest that although IL-12 expedites the clearance of C. abortus infection, this cytokine is not essential for the establishment of a protective host response against the infection.     

Inactivation of the type IV secretion system reduces the Th1 polarization of the immune response to Brucella abortus infection

The Brucella abortus type IV secretion system (T4SS), encoded by the virB operon, is essential for establishing persistent infection in the murine reticuloendothelial system. To gain insight into the in vivo interactions mediated by the T4SS, we compared host responses elicited by B. abortus with those of an isogenic mutant in the virB operon. Mice infected with the B. abortus virB mutant elicited smaller increases in serum levels of immunoglobulin G2a, gamma interferon (IFN-gamma), and interleukin-12p40 than did mice infected with wild-type B. abortus. Despite equal bacterial loads in the spleen, at 3 to 4 days postinfection, levels of IFN-gamma were higher in mice infected with wild-type B. abortus than in mice infected with the virB mutant, as shown by real-time PCR, intracellular cytokine staining, and cytokine levels. IFN-gamma-producing CD4(+) T cells were more abundant in spleens of mice infected with wild-type B. abortus than in virB mutant-infected mice. Similar numbers of IFN-gamma-secreting CD8(+) T cells were observed in the spleens of mice infected with B. abortus 2308 or a virB mutant. These results suggest that early differences in cytokine responses contribute to a stronger Th1 polarization of the immune response in mice infected with wild-type B. abortus than in mice infected with the virB mutant.     

Induction and regulation of Th1-inducing cytokines by bacterial DNA, lipopolysaccharide, and heat-inactivated bacteria

Th1 immune responses, characterized by production of gamma interferon (IFN-gamma), are associated with protective immunity to viruses and intracellular bacteria. Heat-killed Brucella abortus promotes secretion of Th1-inducing cytokines such as interleukin-12 (IL-12) and IFN-gamma and has been used as a carrier to induce Th1 responses to vaccines. To explore which bacterial constituents could mediate this response and how it is regulated, murine spleen cells were cultured with B. abortus derived DNA, lipopolysaccharide (LPS), or whole killed organisms. Each constituent induced similar, substantial amounts of IL-10. However, only B. abortus and B. abortus DNA induced high levels of IFN-gamma and IL-12. B. abortus and B. abortus DNA-stimulated IL-12 production was maximal by 6 to 18 h, while IL-10 production steadily accumulated over this time period. These kinetics suggested that IL-10 may eventually downmodulate the Th1-like cytokine response to B. abortus and B. abortus DNA, which was confirmed by using neutralizing antibody. In the absence of IL-10, B. abortus LPS induced strong IFN-gamma responses, but IL-12 p70 levels were still undetectable from BALB/c spleen cells. LPS induced IL-12 if the spleen cells were primed with IFN-gamma and IL-10 was neutralized, indicating that LPS can stimulate IL-12 production under the most favorable conditions. Responses to Escherichia coli LPS and DNA mirrored the responses to B. abortus components, suggesting that immune effects observed with these constituents may be generalizable to many microbial species. In vivo experiments demonstrated the same hierarchy of responses for IL-12 production. These findings support the likelihood that microbial components, if used as carriers or adjuvants, can differ substantially in their ability to effect a Th1 response.     

Brucella abortus as a potential vaccine candidate: induction of interleukin-12 secretion and enhanced B7.1 and B7.2 and intercellular adhesion molecule 1 surface expression in elutriated human monocytes stimulated by heat-inactivated B. abortus.

Development of a vaccine which is capable of generating a strong cellular immune response associated with gamma interferon (IFN-gamma) production and cytotoxic T-cell development requires that the immunogen be capable of inducing the secretion of interleukin-12 (IL-12), which is a pivotal factor for the differentiation of Th1 or Tc1 cells. We have previously shown that the heat-inactivated gram-negative bacterium Brucella abortus can induce IFN-gamma secretion by T cells. In the present study, we demonstrate that B. abortus and lipopolysaccharide (LPS) from B. abortus can induce IL-12 p40 mRNA expression and protein secretion by human elutriated monocytes (99% pure). p40 mRNA was detected within 4 h, and p40 protein could be measured at 24 h. This induction was abrogated by anti-CD14 monoclonal antibody, suggesting that monocytes recognize B. abortus via their receptor for LPS. The biological activity of IL-12 secreted by B. abortus-stimulated monocytes was demonstrated by its ability to upregulate IFN-gamma mRNA expression in T cells separated from monocytes and B. abortus by a transwell membrane. The B. abortus-induced IL-12 also enhanced NK cytolytic activity against K562 target cells. B. abortus was shown to rapidly increase the expression of the costimulatory molecules B7.1 and B7.2 and intercellular adhesion molecule 1 on human monocytes. Together, these data indicate that B. abortus can directly activate human monocytes and provide the cytokine milieu which would direct the immune response towards Th1-Tc1 differentiation.     

Human peripheral blood CD4+ and CD8+ T cells express Th1-like cytokine mRNA and proteins following in vitro stimulation with heat-inactivated Brucella abortus.

Defining the pattern of lymphokine production associated with Brucella abortus is critical for advancing the development of B. abortus as a vaccine carrier. In the present study we investigated the ability of heat-inactivated B. abortus or lipopolysaccharide from B. abortus to induce lymphokine production from purified human T cells in vitro. Gamma interferon (IFN-gamma), interleukin-2 (IL-2), IL-4, and IL-5 induction was assayed by mRNA-specific PCR and by enzyme-linked immunosorbent assay and bioassay for protein production. Following depletion of monocytes and B cells, B. abortus increased IFN-gamma and IL-2 mRNA expression in purified T cells compared with expression in unstimulated cells. In contrast, no IL-5 mRNA expression and only transient low-level IL-4 mRNA expression and no IL-4 protein secretion were detected. Phytohemagglutinin or phorbol myristate acetate plus ionomycin induced mRNA and protein for all these cytokines. Similar results were obtained with LPS purified from B. abortus. Removal of NK cells did not reduce lymphokine production, and enriched NK cells did not express IFN-gamma mRNA or secrete IFN-gamma protein in response to B. abortus, indicating that NK cells were not the responding population. Both CD4+ and CD8+ populations produced IFN-gamma and IL-2 in response to B. abortus. Preincubation of resting T cells with B. abortus or LPS from B. abortus for 7 days induced their differentiation into Th1-like cells as judged by their subsequent lymphokine response to phorbol myristate acetate plus ionomycin. These results suggest that B. abortus can induce differentiation of Th0 into Th1-type cells.     

Primed peritoneal B lymphocytes are sufficient to transfer protection against Brugia pahangi infection in mice

Lymphatic filariasis is a tropical disease caused by the nematode parasites Wuchereria bancrofti and Brugia malayi. Whereas the protective potential of T lymphocytes in filarial infection is well documented, investigation of the role of B lymphocytes in antifilarial immunity has been neglected. In this communication, we examine the role of B lymphocytes in antifilarial immunity, using Brugia pahangi infections in the murine peritoneal cavity as a model. We find that B lymphocytes are required for clearance of primary and challenge infections with B. pahangi third-stage larvae (L3). We assessed the protective potential of peritoneal B lymphocytes by adoptive transfer experiments. Primed but not na?ve peritoneal B cells from wild-type mice that had been immunized with B. pahangi L3 protected athymic recipients from challenge infection. We evaluated possible mechanisms by which B cells mediate protection. Comparisons of cytokine mRNA expression between B-lymphocyte-deficient and immunocompetent mice following B. pahangi infection suggest that B cells are required for the early production of Th2-type cytokines by peritoneal cells. In addition, B-cell-deficient mice demonstrate a defect in inflammatory cell recruitment to the peritoneal cavity following B. pahangi infection. The data demonstrate a critical role of B lymphocytes in antifilarial immunity in na?ve mice and in the memory response in primed mice.     

Interleukin-10 downregulates protective immunity to Brucella abortus.

In vivo neutralization of interleukin-10 (IL-10) with an anti-IL-10 monoclonal antibody resulted in up to 10-fold fewer bacteria in the spleens of BALB/c mice infected with the virulent Brucella abortus strain 2308. In vitro neutralization of endogenous IL-10 in brucella antigen-stimulated cultures of splenocytes from infected mice resulted in increased gamma interferon production in these cultures, whereas exogenous recombinant IL-10 inhibited the ability of peptone-elicited peritoneal macrophages to control intracellular brucellae. These data suggest that IL-10 may be downregulating the immune response to B. abortus by affecting both macrophage effector function and the production of the protective Th1 cytokine gamma interferon.     

<Emphasis Type="Italic">Brugia malayi</Emphasis> Adult Low Molecular Weight IgG4-Reactive Antigens Induce Differential Cytokine Response in Lymphocytes of Endemic Normal and Asymptomatic Microfilariae Carriers <Emphasis Type="Italic">In Vitro</Emphasis>

To characterize putatively protective immune response in bancroftian filariasis, Th1/Th2 cytokine profile induced in peripheral blood mononuclear cells (PBMCs) of endemic normal (EN) and asymptomatic microfilaremic (ASM) individuals were studied using different molecular weight fractions of Brugia malayi adult soluble antigens (BmA), which are differentially recognized by IgG4 antibodies present in their sera. Infection free and putatively immune individuals living in a filaria endemic area were identified and included in the present study as EN only after careful longitudinal follow up for three years. It was observed that the low molecular weight antigens present in Fr4 and Fr5 induced differential cytokine response; EN individuals showed a strong Th1 bias whereas ASM individuals showed a strong Th2 bias even though both the groups produced Th1 cytokines, albeit of different quantity, when a nonhelminthic antigen like H37Rv whole cell lysate was used. Since antigens present in Fr5 induced a highly polarized response, they should be examined for their diagnostic potential in lymphatic filariasis.     

Ontogeny of Th1 memory responses against a Brucella abortus conjugate

Protective immune responses to intracellular pathogens such as Brucella abortus are characteristically Th1-like. Recently we demonstrated that heat-killed B. abortus (HKBa), a strong Th1 stimulus, conjugated to ovalbumin (HKBA-OVA), but not B. abortus alone, can alter the antigen-specific cytokine profile from Th2- to Th1-like. In this report we study the ability of a single injection of B. abortus to switch a Th2 to a Th1 response in immature mice. One-day- and 1-week-old mice were given a single injection of B. abortus in the absence or presence of OVA, and at maturity mice were challenged with an allergenic preparation, OVA with alum (OVA-A). B. abortus given without OVA did not diminish the subsequent Th2 response in either age group. In contrast, mice receiving a single injection of B. abortus-OVA at the age of 1 week, but not those injected at the age of 1 day, had reversal of the ratio of OVA-specific Th1 to Th2 cells and decreased immunoglobulin E levels after allergen challenge as adults. Within 6 h both 1-day- and 1-week-old mice expressed interleukin-12 p40 mRNA following either B. abortus or B. abortus-OVA administration. However, only the 1-week-old mice exhibited increased expression of gamma interferon (IFN-gamma) mRNA. The absence of the early IFN-gamma response in 1-day-old mice may explain their inability to generate a Th1 memory response. These results suggest that at early stages of immune development, responses to intracellular bacteria may be Th2- rather than Th1-like. Furthermore, they suggest that the first encounter with antigen evokes either a Th1- or a Th2-like response which becomes imprinted, so that subsequent memory responses conform to the original Th bias. This has implications for protection against infectious agents and development of allergic responses.     

Th1 and Th2 cell-associated cytokines in experimental visceral leishmaniasis.

In experimental Leishmania donovani infection in BALB/c mice, initial susceptibility gives way to T-cell-dependent acquired resistance and eventual control over visceral infection. Since various cytokines appear to underlie the host response to Leishmania infection, we examined infected liver tissue for gene expression of cytokines associated with Th1 (gamma interferon [IFN-gamma] and interleukin-2 [IL-2]) and Th2 cells (IL-4 and IL-10). By Northern (RNA) blot analysis, only IFN-gamma mRNA expression was detected in livers of infected euthymic mice. To determine whether activation of Th1 cells develops selectively in this model, qualitative PCR analysis was used. These results indicated that mRNAs for IFN-gamma, IL-2, IL-4, and IL-10 were all induced by L. donovani infection. The potentially negative Th2 cell-associated response did not appear to play a functional role, however, since resistance was acquired, anti-IL-4 monoclonal antibody treatment did not accelerate control over visceral infection, and serum immunoglobulin E levels remained low. As judged by PCR analysis, IL-4 and IL-10 mRNAs were also expressed under three other conditions without apparent effect: in naive euthymic mice treated with IL-2, which induces leishmanicidal activity; in rechallenged immune mice, which resist reinfection; and in nude mice, which fail to control L. donovani. These results suggest that, like other Leishmania species, L. donovani infection may trigger a potentially suppressive Th2 cell-associated cytokine response. However, in T-cell-intact mice able to control L. donovani, this response either is insufficient to influence outcome or more likely is overshadowed by the Th1 cell response.     

Dynamic analysis of splenic Th1 and Th2 lymphocyte functions in mice infected with Schistosoma japonicum.

Recent studies indicate that egg granuloma formation in murine Schistosoma mansoni infection is associated with Th2-mediated immune responses. The present study was designed to analyze dynamically the Th1 and Th2 responses in S. japonicum-infected animals and compare them with the results seen with S. mansoni. C3H mice were infected with 10 to 20 cercariae of S. japonicum and sacrificed 3 to 22 weeks later. Spleen cells were stimulated with parasite antigens (egg and adult worm) or the mitogen concanavalin A. Interleukin-2 (IL-2), IL-4, IL-5, and gamma interferon (IFN-gamma) levels were measured in the culture supernatants by enzyme-linked immunosorbent assay (ELISA) or bioassays. Additionally, cytokine-producing cells were enumerated by ELISPOT. The results show that Th2 cytokine production, characterized by IL-4 and IL-5, represents the major response in the first month after egg laying begins, while the Th1 functions of IFN-gamma and IL-2 production are greatly depressed. However, by 22 weeks Th2 responses have diminished and IFN-gamma production in response to concanavalin A is apparent. IL-2 responses are minimal at all times. In vitro depletion of T-cell subsets indicates that CD4+ cells are the major subset responsible for production of IL-5 at 7 weeks of infection. These findings suggest that, as in the case of S. mansoni infection, S. japonicum-induced immunopathology is temporally associated with the host Th2 response, although other experiments indicate that IFN-gamma is also involved.     

Brucella abortus regulates bovine macrophage-T-cell interaction by major histocompatibility complex class II and interleukin-1 expression

T-cell activation is dependent on nominal antigen associated with major histocompatibility complex (MHC) class II molecules and interleukin-1 (IL-1), both provided by antigen-presenting cells. We have studied the effects of Brucella abortus and recombinant bovine gamma interferon (IFN-gamma) on bovine macrophage expression of MHC class II and IL-1 molecules and subsequent T-cell proliferation in response to B. abortus. When peripheral blood mononuclear cells were cocultured with B. abortus and IFN-gamma, increasing amounts of IFN-gamma, from 1 to 100 U/ml, down regulated T-cell proliferation. Expression of MHC class II molecules on macrophages was increased independently by IFN-gamma or B. abortus treatment. Thus, class II molecule expression was not the cause of down regulation of T-cell proliferation as observed in other systems. However, B. abortus-IFN-gamma-treated macrophages obtained from overnight cultures had minimal membrane IL-1 compared with macrophages treated with B. abortus alone. Loss of membrane IL-1 required IFN-gamma and the o-polysaccharide of the lipopolysaccharide. IFN-gamma at 1 U/ml in combination with B. abortus produced a 32% decrease in T-cell response, while IFN-gamma at 100 U/ml added to B. abortus-treated cultures produced an 82% reduction in T-cell response. Membrane IL-1 levels were not altered when recombinant bovine IFN-alpha or the rough strain 45/20 of B. abortus, which lacks the o-polysaccharide, was used. Secreted IL-1 levels were unaffected by IFN-gamma and B. abortus treatment. The addition of recombinant bovine IL-1 beta (0.001 to 0.1 ng/ml) to B. abortus- and IFN-gamma-treated cultures failed to provide a signal necessary for T-cell proliferation. These data suggest that membrane IL-1 has a key role in T-cell activation in response to B. abortus. When the o-polysaccharide of B. abortus lipopolysaccharide is combined with IFN-gamma at an inappropriate time during an immune response, T-cell proliferation is prevented and cannot be restored by the addition of exogenous IL-1.     

Cytokine responses in acute and persistent human parvovirus B19 infection

The aim of this study was to characterize the proinflammatory and T helper (Th)1/Th2 cytokine responses during acute parvovirus B19 (B19) infection and determine whether an imbalance of the Th1/Th2 cytokine pattern is related to persistent B19 infection. Cytokines were quantified by multiplex beads immunoassay in serum from B19-infected patients and controls. The cytokine responses were correlated with B19 serology, quantitative B19 DNA levels and clinical symptoms. In addition to a proinflammatory response, elevated levels of the Th1 type of cytokines interleukin (IL)-2, IL-12 and IL-15 were evident at time of the initial peak of B19 viral load in a few patients during acute infection. This pattern was seen in the absence of an interferon (IFN)-gamma response. During follow-up (20-130 weeks post-acute infection) some of these patients had a sustained Th1 cytokine response. The Th1 cytokine response correlated with the previously identified sustained CD8+ T cell response and viraemia. A cross-sectional study on patients with persistent B19 infection showed no apparent imbalance of their cytokine pattern, except for an elevated level of IFN-gamma response. No general immunodeficiency was diagnosed as an explanation for the viral persistence in this later group. Neither the acutely infected nor the persistently infected patients demonstrated a Th2 cytokine response. In conclusion, the acutely infected patients demonstrated a sustained Th1 cytokine response whereas the persistently infected patients did not exhibit an apparent imbalance of their cytokine pattern except for an elevated IFN-gamma response.     

Interleukin-12 regulation of host defenses against Coccidioides immitis.

We have previously reported on the alternate regulation of gamma interferon (IFN-gamma) and interleukin-4 (IL-4) in inbred mouse strains which differ in their susceptibility to Coccidioides immitis. The genetically resistant DBA/2 mice manifest a predominant T-helper 1 (Th1) response, with early production of IFN-gamma, whereas susceptible BALB/c mice show an early production of the Th2 cytokine IL-4. Since IL-12 is one cytokine that can act early during host defenses to promote the differentiation of cytokine production towards IFN-gamma and thus may promote expression of a protective immune response, we investigated the role of IL-12 in resistance to C. immitis. Administration of recombinant IL-12 to the susceptible mouse strain before and after systemic (intraperitoneal) challenge with C. immitis significantly ameliorated the course of the disease, as measured by a reduction in the fungal load in the lungs, liver, and spleen. Analysis of the cytokine mRNA in lungs from infected BALB/c mice revealed that the protective effect of recombinant IL-12 was accompanied by a shift from a Th2 to a Th1 response. The importance of IL-12 in resistance to this fungus was further established by showing that neutralization of endogenous IL-12 in the resistant DBA/2 mouse strain led to a significant increase in the fungal burden in pulmonary and extrapulmonary tissues. These results establish that IL-12 plays a pivotal role in the host defense against systemic challenge with C. immitis.     

Synergism of gamma interferon and interleukin-5 in the control of murine filariasis

There has been a prevailing perception that Th1 and Th2 immune responses induce antagonistic immune effector mechanisms during an infection. We investigated the role of the Th1 cytokine gamma interferon (IFN-gamma) and the Th2 cytokine interleukin-5 (IL-5) in murine filariasis infections with the rodent filarial nematode Litomosoides sigmodontis with regard to immune responses to the parasite. Earlier data showed an important role for IL-5 and IFN-gamma in effective immune responses to filarial infection. Therefore, in this study it was asked whether IL-5 and IFN-gamma act synergistically or antagonistically. Indeed, IL-5 as well as IFN-gamma knockout (KO) mice show a higher worm load than the wild-type controls. IFN-gamma/IL-5 double-KO mice had a significantly higher worm load than any of the single-KO mice, suggesting a synergism between IFN-gamma and IL-5 in controlling worm infection. Neutrophils are known to play an important role for the containment and encapsulation process of the worms. In infected IFN-gamma KO, IL-5 KO, and IFN-gamma/IL-5 double-KO mice, neutrophils were significantly reduced in chemotactic activity levels compared to controls. In addition, the level of phagocytosis activity of neutrophils from IFN-gamma/IL-5 double-KO mice was further decreased in comparison to that of the single-KO mice. Levels of tumor necrosis factor alpha, which is an important factor for neutrophil activation, were found to be reduced in macrophages from KO mice. In conclusion, these results argue for immune effector mechanisms in murine filarial infection that are dependent on both IFN-gamma and IL-5. Synergistic effects of the two cytokines may be mediated, at least in part, by neutrophils for the control of adult worms.     

Response of Armigeres subalbatus (Diptera: Culicidae) to intraperitoneally isolated Brugia spp. microfilariae

The relationship between mosquito and parasite involves a delicate balance that is influenced not only by the mosquito but also by parasite determinants. Using the biologically and morphologically similar parasites Brugia malayi and Brugia pahangi and the mosquito Armigeres subalbatus (Coquillett) (Diptera: Culicidae), it should be possible to dissect out the key elements involved in initiating or avoiding an immune response, known as melanotic encapsulation, because in this mosquito B. malayi microfilariae (mf) are melanized and destroyed, but B. pahangi mf develop normally into infective-stage larvae. Because of limitations in isolating sufficient mf from the circulation of an infected mammalian host, Brugia spp. mf that can be obtained in large numbers from the peritoneal cavity of an infected host were tested to ascertain the immune response of Ar. subalbatus to this source of mf. Results indicate that the immune response of Ar. subalbatus against intraperitoneal (i.p.) Brugia spp. mf mimics that which is observed when this mosquito is exposed to mf-infected animals, indicating that i.p. mf are similar to those mf that circulate naturally in the blood of the vertebrate host. Therefore, the i.p. mf should serve as an excellent source of material for genomic and proteomic studies designed to analyze the role of the parasite in influencing the immune response of the mosquito.     

Modulation of experimental blood stage malaria through blockade of the B7/CD28 T-cell costimulatory pathway

Recent studies have implicated cytokines associated with CD4+ T lymphocytes of both T helper (Th)1 and Th2 subsets in resistance to experimental blood stage malaria. As the B7/CD28 costimulatory pathway has been shown to influence the differentiation of Th cell subsets, we investigated the contribution of the B7 molecules CD80 and CD86 to Th1/Th2 cytokine and immunoglobulin isotype profiles and to the development of a protective immune response to malaria in NIH mice infected with Plasmodium chabaudi. Effective blockade of CD86/CD28 interaction was demonstrated by elimination of interleukin (IL)-4 and up-regulation of interferon (IFN)-gamma responses by P. chabaudi-specific T cells and by reduction of P. chabaudi-specific immunoglobulin G1 (IgG1). The shift towards a Th1 cytokine pattern corresponded with efficient control of acute parasitaemia but an inability to resolve chronic infection. Moreover, combined CD80/CD86 blockade by using anti-CD80 and anti-CD86 monoclonal antibodies raised IFN-gamma production over that seen with CD86 blockade alone, with augmentation of this Th1-associated cytokine reducing levels of peak primary parasitaemia. These results demonstrate that IL-4 production by T cells in P. chabaudi-infected NIH mice is dependent upon CD86/CD28 interaction and that IL-4 and IFN-gamma contribute significantly, at different times of infection, to host resistance to blood stage malaria. In addition, combined CD80/CD86 blockade resulted in preferential expansion of IFN-gamma-producing T cells during P. chabaudi infection, suggesting that costimulatory pathways other than B7/CD28 may contribute to T-cell activation during continuous antigen stimulation. This study indicates a role for B7/CD28 costimulation in modulating the CD4+ T-cell response during malaria, and further suggests involvement of this pathway in other infectious and autoimmune diseases in which the Th cell immune response is also skewed.