Production of IFN-gamma and IL-10 to Shigella invasins by mononuclear cells from volunteers orally inoculated with a Shiga toxin-deleted Shigella dysenteriae type 1 strain

Volunteers were orally administered invasive, non-Shiga toxin-producing Shigella dysenteriae 1 to establish a challenge model to assess vaccine efficacy. In stepwise fashion, four separate groups were given 3 x 10(2), 7 x 10(3), 5 x 10(4), or 7 x 10(5) CFU. Using PBMC, proliferative responses and cytokine production were measured to S. dysenteriae whole-cell preparations and to purified recombinant invasion plasmid Ags (Ipa) C and IpaD. Anti-LPS and anti-Ipa Abs and Ab-secreting cells were also evaluated. Preinoculation PBMC produced considerable quantities of IL-10 and IFN-gamma, probably secreted by monocytes and NK cells, respectively, of the innate immune system. Following inoculation, PBMC from 95 and 87% of volunteers exhibited an increased production of IFN-gamma and IL-10, respectively, in response to Shigella Ags. These increases included responses to IpaC and IpaD among those volunteers receiving the lowest inoculum. No IL-4 or IL-5 responses were detected. Whereas there were no Ab or Ab-secreting cell responses in volunteers receiving the lowest inoculum, other dose groups had moderate to strong anti-LPS and anti-Ipa responses. These results suggest that in humans, type 1 responses play an important role in mucosal and systemic immunity to S. dysentariae 1.     

Filarial parasites induce NK cell activation, type 1 and type 2 cytokine secretion, and subsequent apoptotic cell death

NK cells are an important source of early cytokine production in a variety of intracellular viral, bacterial, and protozoan infections; however, the role of NK cells in extracellular parasitic infections such as filarial infections is not well-defined. To investigate the role of NK cells in filarial infections, we have used an in vitro model system of culturing live infective-stage larvae (L3) or live microfilariae (Mf) of Brugia malayi, a causative agent of human lymphatic filariasis, with PBMC of normal individuals. We found that NK cells undergo early cell activation and produce IFN-gamma and TNF-alpha within 24 h after stimulation with both live L3 and Mf. Interestingly, NK cells also express IL-4 and IL-5 at this time point in response to live Mf but not L3. This is accompanied by significant alterations in NK cell expression of costimulatory molecules and natural cytotoxicity receptors. This activation is dependent on the presence of monocytes in the culture, IL-12, and direct contact with live parasites. The early activation event is subsequently followed by apoptosis of NK cells involving a caspase-dependent mechanism in response to live L3 but not live Mf. Thus, the NK cell-parasite interaction is complex, with filarial parasites inducing NK cell activation and cytokine secretion and finally NK cell apoptosis, which may provide an additional mechanism of down-regulating the host immune response.     

Human metapneumovirus elicits weak IFN-gamma memory responses compared with respiratory syncytial virus

Human metapneumovirus (MPV) is a recently discovered pathogen that causes repeated lower respiratory tract infections beginning in infancy. The prevalence, nature and control of human regulatory responses to MPV are unknown. In this study, we develop and optimize systems to evaluate MPV-driven cytokine responses. Using primary culture of human PBMC from previously exposed adults, MPV-stimulated responses were directly compared with those elicited by genetically and clinically similar respiratory syncytial virus (RSV). Intense IL-6 production was evident following culture with infectious or inactivated RSV. MPV elicited IL-6 responses averaging 3.5-fold more intense (p < 0.001). Virus-dependent expression of IL-11, IL-12, IFN-alpha, and other innate immunity cytokines differed little between MPV and RSV. When examining adaptive immunity, RSV infection elicited strong IFN-gamma responses by all 60 adults. In marked contrast, MPV elicited IFN-gamma in a lower frequency of adults (p < 0.002) and at levels averaging 6-fold weaker (p < 0.001). These Th1-dominated responses were CD4, CD8, CD86 dependent, and were closely paralleled by strong virus-driven IL-10 and CCL5 production. For MPV and RSV, Th2 (IL-5, IL-13) responses were sporadic, occurring in 10-40% of the population. Thus, MPV and RSV, although both ubiquitous and leading to very high levels of infection, seroconversion, and clinically similar presentation in the population, evoke distinct innate and adaptive T cell-dependent cytokine responses. Although both viruses yield Th1-dominated responses with strong IL-10 and CCL5 production, MPV restimulation results in markedly more robust IL-6 and significantly weaker adaptive cytokine responses, in both prevalence and intensity, than does RSV.     

Regulatory T cells in human lymphatic filariasis: stronger functional activity in microfilaremics

Infection with filarial parasites is associated with T cell hyporesponsiveness, which is thought to be partly mediated by their ability to induce regulatory T cells (Tregs) during human infections. This study investigates the functional capacity of Tregs from different groups of filarial patients to suppress filaria-specific immune responses during human filariasis. Microfilaremic (MF), chronic pathology (CP) and uninfected endemic normal (EN) individuals were selected in an area endemic for Brugia timori in Flores island, Indonesia. PBMC were isolated, CD4CD25(hi) cells were magnetically depleted and in vitro cytokine production and proliferation in response to B. malayi adult worm antigen (BmA) were determined in total and Treg-depleted PBMC. In MF subjects BmA-specific T and B lymphocyte proliferation as well as IFN-gamma, IL-13 and IL-17 responses were lower compared to EN and CP groups. Depletion of Tregs restored T cell as well as B cell proliferation in MF-positives, while proliferative responses in the other groups were not enhanced. BmA-induced IL-13 production was increased after Treg removal in MF-positives only. Thus, filaria-associated Tregs were demonstrated to be functional in suppressing proliferation and possibly Th2 cytokine responses to BmA. These suppressive effects were only observed in the MF group and not in EN or CP. These findings may be important when considering strategies for filarial treatment and the targeted prevention of filaria-induced lymphedema.     

A distinct IL-18-induced pathway to fully activate NK T lymphocytes independently from TCR engagement

NK T lymphocytes are characterized by their ability to promptly generate IL-4 and IFN-gamma upon TCR engagement. Here, we demonstrate that these cells can also be fully activated in the absence of TCR cross-linking in response to the proinflammatory cytokine IL-18 associated with IL-12. NK T cells stimulated with IL-18 plus IL-12 proliferated, killed Fas+ target cells, and produced high levels of IFN-gamma without IL-4. In these conditions, IFN-gamma production was at least 10-fold higher than that upon TCR cross-linking. Interestingly, a 2-h pretreatment with IL-12 plus IL-18 sufficed to maintain the high IFN-gamma-producing potential during subsequent stimulation with anti-TCR mAbs or with the specific Ag alpha-galactosylceramide. Similar effects were observed in vivo, because splenic CD4+ NK T cells from MHC class II-deficient mice secreted IFN-gamma without further stimulation when removed 2 h after a single injection of IL-12 plus IL-18. In conclusion, our evidence for activation of NK T lymphocytes in response to IL-18 plus IL-12 in the absence of TCR engagement together with the maintenance of preferential IFN-gamma vs IL-4 production upon subsequent exposure to specific Ags is consistent with the active participation of this cell population in innate as well as acquired cellular immune responses.     

IL-12, IFN-gamma, and T cell proliferation to measles in immunized infants

Measles infection in infants is associated with severe complications, and secondary infections are attributed to generalized immunosuppression. Measles binding to its monocyte receptor down-regulates IL-12 which is expected to diminish Th1-like cytokine responses, including IFN-gamma. Whether young infants can be immunized effectively against measles is an important public health issue. We evaluated Ag-specific IL-12, IFN-gamma, and T cell responses of infants at 6 (n = 60), 9 (n = 46), or 12 mo (n = 56) of age and 29 vaccinated adults. IL-12 and IFN-gamma release by PBMC stimulated with measles Ag increased significantly after measles immunization in infants. IL-12 and IFN-gamma concentrations were equivalent in younger and older infants, but IL-12 concentrations were significantly lower in infants than in adults (p = 0.04). IL-12 production by monocytes was down-regulated by measles; the addition of recombinant human IL-12 enhanced IFN-gamma production by PBMC stimulated with measles Ag, but infant T cells released significantly less IFN-gamma than adult T cells under this condition. Of particular interest, the presence of passive Abs to measles had no effect on the specific T cell proliferation or IFN-gamma production after measles stimulation. Cellular immunity to measles infection and vaccination may be limited in infants compared with adults as a result of less effective IFN-gamma and IL-12 production in response to measles Ags. These effects were not exaggerated in younger infants compared with effects in infants who were immunized at 12 mo. In summary, infant T cells were primed with measles Ag despite the presence of passive Abs, but their adaptive immune responses were limited compared with those of adults.     

Altered cytokine responses of dengue-specific CD4+ T cells to heterologous serotypes

The interplay of different inflammatory cytokines induced during a dengue (DEN) virus infection plays a role in either protection or increased disease severity. We measured the frequencies and characterized the cytokine responses of DEN virus-specific memory CD4+ T cells in PBMC of six volunteers who received experimental live attenuated monovalent DEN vaccines. IFN-gamma and TNF-alpha responses to inactivated DEN Ags were detected in up to 0.54 and 1.17% of total circulating CD4+ T cells, respectively. Ags from the homologous serotype elicited the highest IFN-gamma response. The ratio of TNF-alpha- to IFN-gamma-producing CD4+ T cells was higher after stimulation with Ags from heterologous DEN serotypes. Peptide-specific CD4+ T cell frequencies of up to 0.089% were detected by direct staining using HLA class II tetramers. IFN-gamma and TNF-alpha responses to individual HLA class II-restricted peptide epitopes were detected in up to 0.05 and 0.27% of CD4+ T cells, respectively. Peptide sequences from the homologous serotype elicited a variety of cytokine response patterns. TNF-alpha- to IFN-gamma-positive CD4+ T cell ratios varied between peptides, but the ratio of the sum of responses was highest against heterologous serotypes. These results demonstrate epitope sequence-specific differences in T cell effector function. These patterns of effector responses may play a role in the immunopathogenesis of DEN hemorrhagic fever.     

Diesel exhaust particles suppress in vivo IFN-gamma production by inhibiting cytokine effects on NK and NKT cells

Diesel exhaust particles (DEP) have strong, selective Th2 adjuvant activity when inhaled with conventional Ags. We used a novel technique for measuring in vivo cytokine production to investigate possible mechanisms by which DEP might promote a Th2 response. Injection of DEP i.p. stimulated IL-6 secretion, but failed to increase IL-4, IL-10, or TNF-alpha secretion, and decreased basal levels of IFN-gamma. When injected with or before LPS, DEP had little effect on the LPS-induced TNF-alpha responses, but partially inhibited the LPS-induced IL-10 response and strongly inhibited the LPS-induced IFN-gamma response. DEP also inhibited the IFN-gamma responses to IL-12, IL-12 plus IL-18, IL-2, and poly(I.C). DEP treatment had little effect on the percentages of NK and NKT cells in the spleen, but inhibited LPS-induced IFN-gamma production by splenic NK and NKT cells. In contrast, DEP failed to inhibit the IFN-gamma response by anti-CD3 mAb-activated NKT cells. Taken together, these observations suggest that DEP inhibit Toll-like receptor ligand-induced IFN-gamma responses by interfering with cytokine signaling pathways that stimulate NK and NKT cells to produce IFN-gamma. Our observations also suggest that DEP may promote a Th2 response by stimulating production of inflammatory cytokines while simultaneously inhibiting production of IFN-gamma, and raise the possibility that the same mechanisms contribute to the association between DEP exposure and asthma.     

IL-10 and IL-12 are the main regulatory cytokines in visceral leishmaniasis

Visceral leishmaniasis (VL) is characterized by the absence of cytokines such as IFN-gamma and IL-12. Cure of VL is associated with a restoration of the ability to make these cytokines. The aim of the present study was to evaluate the role of IL-12 in the recovery of the ability to produce IFN-gamma and to test whether or not IL-4 IL-10 and/or TGF-beta could suppress IFN-gamma production by PBMC from treated VL patients. High stimulation index (SI) of proliferation was observed in PBMC from subjects stimulated with Leishmania chagasi antigen (181+/-83). Neutralizing IL-12 inhibited lymphoproliferation [stimulation index (SI) of 210+/-114 to 1+/-0.6 (P<0.01)] and/or the production of IFN-gamma [2792+/-402 pg/ml to 407+/-449 pg/ml (P<0.01)]. Recombinant IL-10 abrogated the lymphoproliferation (SI=2+/-3) while recombinant IL-4 or TGF-beta had no effect on this response (147+/-22 and 194+/-12 respectively). IFN-gamma was high when PBMCs were stimulated with L. chagasi (873+/-400 pg/ml) and this was abrogated by the addition of IL-10 (5+/-2 pg/ml). In contrast neither IL-4 or TGF-beta suppressed IFN-gamma production (837+/-244 pg/ml and 759+/-523 pg/ml). These results indicate that IL-12 plays an important role in the ability of treated VL patients to make IFN-gamma and that IL-10 but not IL-4 or TGF-beta inhibits this response.     

DNA vaccines,combining form of antigen and method of delivery to raise a spectrum of IFN-gamma and IL-4-producing CD4+ and CD8+ T cells

DNA-based immunizations have been used to determine the patterns of type 1 and type 2 cytokines that can be induced in vivo for Ag-specific CD4(+) and CD8(+) T cells. IL-4 was used as a signature cytokine for a type 2 T cell response and IFN-gamma as the signature cytokine for a type 1 response. Gene gun deliveries of secreted Ags were used to bias responses toward type 2 and saline injections of cell-associated Ags to bias responses toward type 1. The studies revealed that gene gun bombardments of DNAs expressing secreted Ags strongly biased responses toward type 2, inducing IL-4-producing CD8(+) as well as CD4(+) T cells. Saline injections of DNAs expressing cell-associated Ags strongly biased responses toward type 1, inducing IFN-gamma-producing CD8(+) and CD4(+) cells. A mixed type 1/type 2 response of IFN-gamma-producing CD8(+) T cells and IL-4-producing CD4(+) T cells was found for gene gun deliveries of cell-associated Ags. Saline injections of secreted Ags raised a weakly type 1-biased response characterized by only slightly higher frequencies of IFN-gamma- than IL-4-producing CD4(+) and CD8(+) T cells. Studies in B cell knockout and hen egg lysozyme Ig transgenic mice revealed that B cells were required for the generation of IL-4-producing CD8(+) T cells.     

The serpin secreted by Brugia malayi microfilariae, Bm-SPN-2, elicits strong, but short-lived, immune responses in mice and humans

Understanding the basic immunology of an infectious disease requires insight into the pattern of T cell reactivity and specificity. Although lymphatic filariasis is a major tropical disease, the predominant T cell Ags of filarial species such as Brugia malayi are still undefined. We have now identified a prominent T cell Ag from B. malayi microfilariae (Mf) as Bm-SPN-2, a serpin secreted exclusively by this stage. Mf-infected mice mounted strong, but short-lived, Bm-SPN-2-specific Th1 responses, measured by in vitro production of IFN-gamma, but not IL-4 or IL-5, 14 days postinfection. By day 35, responsiveness to Bm-SPN-2 was lost despite enhanced reactivity to whole Mf extract. Single immunization with Mf extract also stimulated typical Th1 reactions to Bm-SPN-2, but IgG1 Ab responses dominated after repeated immunizations. Human patients displayed potent humoral responses to Bm-SPN-2 in both IgG1 and IgG4 subclasses. Thus, 100% (20 of 20) of the microfilaremic (MF(+)) patients bore IgG4 responses to Bm-SPN-2, while only 30% of endemic normal subjects were similarly positive. Following chemotherapy, Bm-SPN-2-specific Abs disappeared in 12 of 13 MF(+) patients, although the majority remained seropositive for whole parasite extract. PBMC from most, but not all, endemic subjects were induced to secrete IFN-gamma when stimulated with Bm-SPN-2. These findings demonstrate that Bm-SPN-2 is recognized by both murine and human T and B cells and indicate that their responses are under relatively stringent temporal control. This study also provides the first example of a stage-specific secreted molecule that acts as a major T cell Ag from filarial parasites and is a prime candidate for a serodiagnostic probe.     

IL-2 receptor blockade inhibits late,but not early,IFN-gamma and CD40 ligand expression in human T cells: disruption of both IL-12-dependent and -independent pathways of IFN-gamma production

mAbs directed against the alpha-chain (Tac/CD25) of the IL-2R are an emerging therapy in both transplantation and autoimmune disease. However, the mechanisms underlying their therapeutic efficacy have not been fully elucidated. Therefore, we examined the effect of IL-2R blockade on Th1 and Th2 cytokine production from human PBMC. Addition of a humanized anti-Tac Ab (HAT) to activated PBMC cultures inhibited IFN-gamma production from CD4 and CD8 T cells by 80-90%. HAT partially inhibited production of TNF-alpha and completely inhibited production of IL-4, IL-5, and IL-10. Furthermore, IL-12, a central regulatory cytokine that induces IFN-gamma, was undetectable in treated cultures. As T cell-dependent induction of IL-12 is regulated via CD40/CD40 ligand (CD40L) interactions, we examined the effect of HAT on CD40L expression. We found CD40L expression to be biphasic with an early (6 h) peak that is CD28/IL-2-independent, but a later peak (48 h) being CD28/IL-2-dependent and inhibited by HAT. Similarly, IFN-gamma production at 6 h was CD28/IL-2-independent but CD28/IL-2-dependent and inhibited by HAT at 48 h. Nonetheless, addition of rCD40L or exogenous IL-12 to HAT-treated cultures could not restore IFN-gamma production. The IFN-gamma deficit in such cultures appears to be due to a direct inhibition by HAT of IL-12-independent IFN-gamma production from T cells rather than altered expression of either the IL-12Rbeta1 or IL-12Rbeta2 chains. These data demonstrate that IL-2 plays a critical role in the regulation of Th1 and Th2 responses and impacts both IL-12-dependent and -independent IFN-gamma production.     

Role of costimulatory molecules in immune response of patients with cutaneous leishmaniasis

T cell-mediated immunity is critical in resistance against Leishmania parasites, and T cell activation requires signals provided by costimulatory molecules. Herein we evaluated the role of costimulatory molecules on cytokine production and T cell surface molecule expression by peripheral blood mononuclear cells (PBMC) from cutaneous leishmaniasis (CL) patients. PBMC from CL patients were stimulated with soluble Leishmania antigen (SLA, 10 microg/ml), in the presence or absence of soluble CTLA4-Ig to block CD28-B7 interaction or in the presence or absence of anti-human CD40L to block CD40-CD40L interaction. Supernatants were harvested to evaluate tumor necrosis factor alpha (TNF-alpha), interleukin 10 (IL-10), transforming growth factor beta (TGF-beta) and interferon gamma (IFN-gamma) production by ELISA. Cells were harvested after 48 h of culture, stained for specific activation markers and analyzed by flow cytometry. Results show that the blockade of CD28-B7 interaction by CTLA4-Ig downmodulated IFN-gamma, IL-10, and TNF-alpha secretion by PBMC from CL patients. No alteration was detected on either TGF-beta production or the expression of CTLA44 or CD25 on CD4+ and CD8+ T cells. When the CD40-CD40L interaction was blockade using anti-CD40L, we did not observe changes in cytokine production or in surface molecule expression. The blockade of the CD28-B7 interactions by CTLA4-Ig also did not alter cytokine production in volunteers immunized against tetanus toxoid (TT). Taken together, these data suggest that the interaction of CTLA4 and CD28-B7 is a TGF-beta-independent mechanism that specifically downmodulates the immune response in cutaneous leishmaniasis patients.     

Mechanisms of the natural reactivity of lymphocytes from noninfected individuals to membrane-associated Leishmania infantum antigens

Membrane-associated Leishmania Ags (MLA) or soluble Leishmania Ags were used in vitro to stimulate cord blood or PBMC from healthy donors noninfected by Leishmania parasites. MLA, but not soluble Leishmania Ags, constantly induce strong proliferation of cord blood mononuclear cells and PBMC from noninfected individuals. Responding cells are CD3+, CD4+, TCRalphabeta+, CD45RO+, and CD45RA+ and secrete IFN-gamma and IL-10, but not IL-4. MLA do not activate NK cells nor NKT cells. Membrane Ags also induce purified macrophages from noninfected individuals to secrete IL-10 and TNF-alpha, but have no effect on IL-1alpha or IL-12 secretion. The effects of MLA are proteinase K-sensitive and resistant to lipid extraction. The lymphoproliferative responses are inhibited by anti-HLA-DR Abs and require Ag processing by APCs, excluding that the biological effect of MLA could be attributed to a superantigen. Finally, TCR repertoire analysis shows that the T cell expansion induced by MLA uses TCR with various variable beta segment rearrangements and CDR3 lengths, features much more characteristic to those observed with a polyclonal activator than with a conventional Ag. These results suggest a particular mechanism developed during the host's natural response to Leishmania parasites that allows direct activation of naive CD4 lymphocytes by parasite membrane-associated Ags.     

Parasite antigen-driven basophils are a major source of IL-4 in human filarial infections

Basophil contribution to the IL-4 pool in filarial infections was assessed using PBMC from 20 patients with active filarial infections and from 9 uninfected subjects. Patient basophils released histamine in response to Brugia malayi Ag (BmAg). They also released IL-4 within 2 h after exposure to BmAg, as assessed by intracellular cytokine flow cytometry. This IL-4 induction was Ag specific, as IL-4 was not detected in BmAg-exposed basophils obtained from uninfected subjects. Although there were, on average, 64 times more CD4(+) T cells than basophils in the peripheral circulation of filaria-infected patients, the absolute numbers of basophils and CD4(+) T cells producing IL-4 per 100000 PBMC were equivalent (geometric mean: 16 IL-4-producing basophils/100000 PBMC vs 22 IL-4-producing CD4(+) T cells/100000 PBMC). Basophils also released IL-4 in response to both low and high concentrations of BmAg, whereas CD4(+) T cells released IL-4 only after incubation with a high concentration of BmAg, raising the possibility that basophils, due to their lower threshold for activation, may actually release IL-4 more frequently than CD4(+) T cells in vivo. Furthermore, IL-4 production in vitro by Ag-stimulated purified basophils or CD4(+) T cells provided evidence that basophils release greater quantities of IL-4 per cell than CD4(+) T cells in response to BmAg. These results suggest that, when Ag-specific IgE is present in a filaria-infected individual, basophils function to amplify the ongoing Th2 response by releasing IL-4 in greater amounts and possibly more frequently than CD4(+) T cells in response to filarial Ag.     

Gammadelta T cell function varies with the expressed WC1 coreceptor

WC1 molecules are transmembrane glycoproteins belonging to the scavenger receptor cysteine-rich family and uniquely expressed on gammadelta T cells. Although participation of WC1+ gammadelta T cells in immune responses is well established, very little is understood regarding the significance of expressing different forms of the WC1 molecule. Two forms previously identified by mAbs, i.e., WC1.1 and WC1.2, are expressed by largely nonoverlapping subpopulations of gammadelta T cells. In this study it was shown that expression of the WC1.1 coreceptor was the main indicator of proliferation and IFN-gamma production in response to autologous and bacterial Ags as well as for IFN-gamma production without proliferation in Th1-polarizing, IL-12-containing cultures. Nevertheless, after culture in either Th1-polarizing or neutral conditions, mRNA was present for both T-bet and GATA-3 as well as for IL-12Rbeta2 in WC1.1+ and WC1.2+ subpopulations, and neither produced IL-4 under any conditions. Although the steady decrease in the proportion of WC1.1+ cells, but not WC1.2+ cells, within PBMC with animal aging suggested that the two subpopulations may have different roles in immune regulation, cells bearing either WC1.1 or WC1.2 expressed mRNA for regulatory cytokines IL-10 and TGF-beta, with TGF-beta being constitutively expressed by ex vivo cells. Overall, the results demonstrate that the form of the WC1 coreceptor expressed on gammadelta T cells divides them into functional subsets according to IFN-gamma production and proliferative capacity to specific stimuli as well as with regard to representation within PBMC. Finally, evidence is provided for minor differences in the intracytoplasmic tail sequences of WC1.1 and WC1.2 that may affect signaling.     

Hepatitis C virus-specific Th17 cells are suppressed by virus-induced TGF-beta

IL-17-secreting T (Th17) cells play a protective role in certain bacterial infections, but they are major mediators of inflammation and are pathogenic in organ-specific autoimmune diseases. However, human Th17 cells appear to be resistant to suppression by CD4(+)CD25(+)FoxP3(+) regulatory T cells, suggesting that they may be regulated by alternative mechanisms. Herein we show that IL-10 and TGF-beta suppressed IL-17 production by anti-CD3-stimulated PBMC from normal individuals. TGF-beta also suppressed IL-17 production by purified CD4(+) T cells, whereas the inhibitory effect of IL-10 on IL-17 production appears to be mediated predominantly by its effect on APC. An examination of patients infected with hepatitis C virus (HCV) demonstrated that Ag-specific Th17 cells are induced during infection and that these cells are regulated by IL-10 and TGF-beta. PBMC from HCV Ab-positive donors secreted IL-17, IFN-gamma, IL-10, and TGF-beta in response to stimulation with the HCV nonstructural protein 4 (NS4). Furthermore, NS4 induced innate TGF-beta and IL-10 expression by monocytes from normal donors and at higher levels from HCV-infected patients. Neutralization of TGF-beta, and to a lesser extent IL-10, significantly enhanced NS4-specific IL-17 and IFN-gamma production by T cells from HCV-infected donors. Our findings suggest that both HCV-specific Th1 and Th17 cells are suppressed by NS4-induced production of the innate anti-inflammatory cytokines IL-10 and TGF-beta. This may represent a novel immune subversion mechanism by the virus to evade host-protective immune responses. Our findings also suggest that TGF-beta and IL-10 play important roles in constraining the function of Th17 cells in general.     

Repeated exposure induces periportal fibrosis in Schistosoma mansoni-infected baboons: role of TGF-beta and IL-4

Recently, we observed that repeated Schistosoma mansoni infection and treatment boost Th2-associated cytokines and TGF-beta production in baboons. Other studies have shown that some chronically infected baboons develop hepatic fibrosis. Because TGF-beta, IL-2, and IL-4 have been shown to participate in development of fibrosis in murine schistosomiasis, the present study examined whether repeated exposure stimulates hepatic fibrosis in olive baboons. To test this hypothesis, animals were exposed to similar numbers of S. mansoni cercariae given once or repeatedly. After 19 wk of infection, animals were cured with praziquantel and reinfected once or multiple times. Hepatic granulomatous inflammation and fibrosis were assessed from serial liver biopsies taken at weeks 6, 9, and 16 after reinfection and egg Ag (schistosome egg Ag)-specific cytokine production by PBMC were measured simultaneously. Periportal fibroblast infiltration and extracellular matrix deposition (fibrosis), angiogenesis, and biliary duct hyperplasia developed in some animals. The presence and amount of fibrosis directly correlated with the frequency of exposure. Fibrosis was not associated with adult worm or tissue egg burden. The amount of fibrosis correlated with increased schistosome egg Ag-driven TGF-beta at 6, 9, and 16 wk postinfection (rs = 0.9, 0.8, and 0.54, respectively, all p < 0.01) and IL-4 production (p = 0.02) at 16 wk postinfection and not IFN-gamma, IL-2, IL-5, or IL-10. These data suggest that repeated exposure is a risk factor for periportal fibrosis by a mechanism that primes lymphocytes to produce increased levels of profibrotic molecules that include TGF-beta and IL-4.