Plasmodium falciparum liver-stage antigen-1 peptide-specific interferon-gamma responses are not suppressed during uncomplicated malaria in African children.

Liver-stage antigen (LSA)-1 is a candidate vaccine molecule for Plasmodium falciparum malaria, but knowledge of the evolution of naturally acquired immune responses to LSA-1 in African children is lacking. We therefore assessed cellular immune responses to two defined T cell epitopes of LSA-1, during and after uncomplicated P. falciparum malaria in a group of Gabonese children. In terms of their prevalence, interferon (IFN)-gamma responses of peripheral blood mononuclear cells (PBMC) to an LSA-1 N-terminal peptide, T1, were significantly higher when measured during the acute phase compared with convalescence. IFN-gamma responses to the LSA-J (hinge region) peptide showed a similar profile, but at a lower prevalence. Depletion experiments confirmed that CD8+ T cells are a major source of peptide-driven IFN-gamma, but both lymphoproliferation and the production of IL-10 in response to either of the peptides was low in all children at all times. PBMC from 25% of the children failed to produce IFN-gamma in response to either peptide at any time-point. The results suggest that lymphocytes producing IFN-gamma in response to at least one T cell epitope of LSA-1 are most frequent in the peripheral circulation during the acute phase of P. falciparum malaria. Thus, in this case, the generalised suppression of cell-mediated responses which characterises acute malaria does not affect liver-stage antigen-specific IFN-gamma production. These findings imply that measurements of the frequency of parasite antigen-specific cellular immune responses in clinically healthy individuals may represent significant underestimations, which has important implications for the design of field-based vaccine antigen-related studies.     

P. falciparum enhances HIV replication in an experimental malaria challenge system

Co-infection with HIV and P. falciparum worsens the prognosis of both infections; however, the mechanisms driving this adverse interaction are not fully delineated. To evaluate this, we studied HIV-1 and P. falciparum interactions in vitro using peripheral blood mononuclear cells (PBMCs) from human malaria na?ve volunteers experimentally infected with P. falciparum in a malaria challenge trial. PBMCs collected before the malaria challenge and at several time points post-infection were infected with HIV-1 and co-cultured with either P. falciparum infected (iRBCs) or uninfected (uRBCs) red blood cells. HIV p24Ag and TNF-α, IFN-γ, IL-4, IL-6, IL-10, IL-17, and MIP-1α were quantified in the co-culture supernatants. In general, iRBCs stimulated more HIV p24Ag production by PBMCs than did uRBCs. HIV p24Ag production by PBMCs in the presence of iRBCs (but not uRBCs) further increased during convalescence (days 35, 56, and 90 post-challenge). In parallel, iRBCs induced higher secretion of pro-inflammatory cytokines (TNF-α, IFN-γ, and MIP-1α) than uRBCs, and production increased further during convalescence. Because the increase in p24Ag production occurred after parasitemia and generalized immune activation had resolved, our results suggest that enhanced HIV production is related to the development of anti-malaria immunity and may be mediated by pro-inflammatory cytokines.     

Plasmodium falciparum infection causes proinflammatory priming of human TLR responses

TLRs are a major group of pattern recognition receptors that are crucial in initiating innate immune responses and are capable of recognizing Plasmodium ligands. We have investigated TLR responses during acute experimental P. falciparum (P.f.) infection in 15 malaria-naive volunteers. TLR-4 responses in whole blood ex vivo stimulations were characterized by significantly (p < 0.01) up-regulated proinflammatory cytokine production during infection compared with baseline, whereas TLR-2/TLR-1 responses demonstrated increases in both proinflammatory and anti-inflammatory cytokine production. Responses through other TLRs were less obviously modified by malaria infection. The degree to which proinflammatory TLR responses were boosted early in infection was partially prognostic of clinical inflammatory parameters during the subsequent clinical course. Although simultaneous costimulation of human PBMC with P.f. lysate and specific TLR stimuli in vitro did not induce synergistic effects on cytokine synthesis, PBMC started to respond to subsequent TLR-4 and TLR-2 stimulation with significantly (p < 0.05) increased TNF-alpha and reduced IL-10 production following increasing periods of preincubation with P.f. Ag. In contrast, preincubation with preparations derived from other parasitic, bacterial, and fungal pathogens strongly suppressed subsequent TLR responses. Taken together, P.f. primes human TLR responses toward a more proinflammatory cytokine profile both in vitro and in vivo, a characteristic exceptional among microorganisms.     

Innate immune response to malaria: rapid induction of IFN-gamma from human NK cells by live Plasmodium falciparum-infected erythrocytes

To determine the potential contribution of innate immune responses to the early proinflammatory cytokine response to Plasmodium falciparum malaria, we have examined the kinetics and cellular sources of IFN-gamma production in response to human PBMC activation by intact, infected RBC (iRBC) or freeze-thaw lysates of P. falciparum schizonts. Infected erythrocytes induce a more rapid and intense IFN-gamma response from malaria-naive PBMC than do P. falciparum schizont lysates correlating with rapid iRBC activation of the CD3(-)CD56(+) NK cell population to produce IFN-gamma. IFN-gamma(+) NK cells are detectable within 6 h of coculture with iRBC, their numbers peaking at 24 h in most donors. There is marked heterogeneity between donors in magnitude of the NK-IFN-gamma response that does not correlate with mitogen- or cytokine-induced NK activation or prior malaria exposure. The NK cell-mediated IFN-gamma response is highly IL-12 dependent and appears to be partially IL-18 dependent. Exogenous rIL-12 or rIL-18 did not augment NK cell IFN-gamma responses, indicating that production of IL-12 and IL-18 is not the limiting factor explaining differences in NK cell reactivity between donors or between live and dead parasites. These data indicate that NK cells may represent an important early source of IFN-gamma, a cytokine that has been implicated in induction of various antiparasitic effector mechanisms. The heterogeneity of this early IFN-gamma response between donors suggests a variation in their ability to mount a rapid proinflammatory cytokine response to malaria infection that may, in turn, influence their innate susceptibility to malaria infection, malaria-related morbidity, or death from malaria.     

Interleukin-2 reverses T cell unresponsiveness to Plasmodium falciparum-antigen in malaria immune subjects

Peripheral blood mononuclear cells (PBMC) from a large proportion of 34 healthy adult native residents in a malaria endemic area showed null or marginal proliferative response (low-responders) to schizont-enriched Plasmodium falciparum malaria antigen (M.Ag) but good response to pokeweed mitogen. In contrast, substantial proliferative response to M.Ag was observed in 8/8 adult temporary residents with a history of one to three acute malaria episodes. Purified CD4+ T cells preferentially responded to M.Ag, however in low-responders CD4+ T cell proliferation was poor. Moreover, no inhibition of CD4+ T cell proliferation was observed when graded numbers of CD8+ T cells were added in culture. The addition of recombinant interleukin 2 (rIL-2) to M.Ag restored the proliferative response of low-responders' PBMC. This response was M.Ag-specific when CD4+ T cells grown in M.Ag plus rIL-2, but not in rIL-2 alone, were tested in secondary cultures.     

Serum levels of interleukin-18 in patients with uncomplicated Plasmodium falciparum malaria

Interleukin (IL)-18, a newly discovered cytokine produced primarily by macrophages, has been shown to induce gamma interferon (IFN-gamma) production by natural killer cells, to induce the T helper type 1 response. To further elucidate the role of this cytokine in uncomplicated malaria caused by Plasmodium falciparum, serum levels of IL-18, and gamma interferon (IFN-gamma), determined by an immunoenzymatic assay, were analyzed in 40 adult patients, and in 15 healthy control subjects. A significant increase in serum levels of IL-18 was observed in patients with uncomplicated P. falciparum malaria on admission, whereas serum levels of IFN-gamma tended to increase although not significantly. Serum levels of IL-18 decreased three days later, but still remained significantly high, whereas IFN-gamma levels returned to normal levels compared to the controls. No significant correlation was found between parasitemia and serum levels of IL-18 and IFN-gamma. The increase of IL-18 levels during acute and recovery phases of uncomplicated P. falciparum malaria may reflect a proinflammatory role of IL-18 in these patients. An early and effective immune response regulated by proinflammatory Th1 cytokines, including tumor necrosis factor (TNF), interleukin (IL)-12, and possibly IFN-gamma may limit the progression from uncomplicated malaria to severe and life-threatening complications.     

IFN-gamma and IL-10 mediate parasite-specific immune responses of cord blood cells induced by pregnancy-associated Plasmodium falciparum malaria

Available evidence suggests that immune cells from neonates born to mothers with placental Plasmodium falciparum (Pf) infection are sensitized to parasite Ag in utero but have reduced ability to generate protective Th1 responses. In this study, we detected Pf Ag-specific IFN-gamma(+) T cells in cord blood from human neonates whose mothers had received treatment for malaria or who had active placental Pf infection at delivery, with responses being significantly reduced in the latter group. Active placental malaria at delivery was also associated with reduced expression of monocyte MHC class I and II in vivo and following short term in vitro coculture with Pf Ag compared with levels seen in neonates whose mothers had received treatment during pregnancy. Given that APC activation and Th1 responses are driven in part by IFN-gamma and down-regulated by IL-10, we examined the role of these cytokines in modulating the Pf Ag-specific immune responses in cord blood samples. Exogenous recombinant human IFN-gamma and neutralizing anti-human IL-10 enhanced T cell IFN-gamma production, whereas recombinant human IFN-gamma also restored MHC class I and II expression on monocytes from cord blood mononuclear cells cocultured with Pf Ag. Accordingly, active placental malaria at delivery was associated with increased frequencies of Pf Ag-specific IL-10(+)CD4(+) T cells in cord blood mononuclear cell cultures from these neonates. Generation and maintenance of IL-10(+) T cells in utero may thus contribute to suppression of APC function and Pf Ag-induced Th1 responses in newborns born to mothers with placental malaria at delivery, which may increase susceptibility to infection later in life.     

Effect of IL-12 and soluble IL-4 receptor on the herpesvirus infection in human SCID chimeras whose Th2 cells predominate

Th2 cytokines, commonly detected in burn patients, have been shown as inhibitors for the generation of Th1 cells that are essential for the host's resistance against herpes simplex virus type 1 (HSV-1) infection. In this study, the possibility of immunological treatment through the regulation of Th1/Th2 responses was examined in two kinds of human severe combined immunodeficiency (SCID) chimera models reflecting human immune functions. SCID mice injected with a mixture of PBMC from a healthy donor and Th2 cells experimentally generated from the same healthy PBMC (Th2 SCID chimeras) were more susceptible to HSV-1 infection when compared with SCID mice injected with healthy donor PBMC (healthy SCID chimeras). When Th2 SCID chimeras were individually treated with human IL-12 (hIL-12) or human soluble IL-4 receptor (hsIL-4R), hIFN-gamma was not produced in their sera after antihuman CD3 mAb stimulation. However, hIFN-gamma production in sera of Th2 SCID chimeras treated with the combination therapy of hIL-12 and hsIL-4R was recovered at levels observed in healthy SCID chimeras. When Th2 SCID chimeras infected with HSV-1 were treated with saline, hIL-12, hsIL-4R or a combination of hIL-12 and hsIL-4R, 13%, 13%, 25% or 100% of them survived, respectively. Also, Th1 responses (hIFN-gamma production) were demonstrated in Th2 SCID chimeras that became resistant against HSV-1 infection after the combination treatment. These results suggest that individuals whose Th2 cells predominated may be immunologically controlled by the combination treatment between a Th1 response inducer and a Th2 response inhibitor.     

The significance of an increase in soluble interleukin-2 receptor level in colorectal cancer and its biological regulating role in the physiological switching of the immune response cytokine network from TH1 to TH2 and back

 Current research has still not clarified the biological role of soluble interleukin(IL)-2 receptor (sIL-2R) and the significance of its increase in the serum of colon cancer patients compared to healthy subjects. To address these questions at the immunological level in a group of patients and healthy subjects, we determined the sIL-2R level in the serum and its release from peripheral blood mononuclear cells (PBMC) as a function of tumour necrosis factor (TNF) α, IL-1α, IL-1β, IL-2, interferon (IFN) γ, IL-4, IL-6 and IL-10 levels in the serum and PBMC production; and PBMC proliferative responses to IL-2, IL-4 and anti-CD3 monoclonal antibody (CD3), variously combined. The level of sIL-2R in patients’ serum was higher than in healthy subjects and correlated with the stage of advancement. Moreover, while in healthy subjects the serum level of sIL-2R was not significantly correlated with other parameters, in patients it was positively related to IL-4, IL-6 and IL-10 serum levels, PBMC IL-4 production and to the PBMC proliferative response to CD3 and CD3+IL-2; it was negatively correlated to IL-2 serum level and IL-1β PBMC release. A negative connection between IFNγ serum level and the PBMC production of sIL-2R was also found. This suggests that the increase of sIL-2R in the serum of patients, compared to healthy subjects, is involved in the inappropriate expansion of the T helper (TH2) suppressive immune response, which we previously reported. The multivariate statistical method supported the above suggestions and we also found that, in healthy subjects, the up- and down-regulation of sIL-2R in the serum within the physiological ranges seems to have a regulating role in the relationships between TNFα, IFNγ and IL-4, IL-6, contributing to the operation of the cytokine network between TH1 and TH2 cells. However, in patients compared to healthy subjects the increased sIL-2R serum level seems to direct the immune response towards a suppressive type, which may be due to an alteration in the above-mentioned physiological regulating role. Received: 12 April 1997 / Accepted: 4 September 1997     

Recombinant human IL-2 overcomes genetic nonresponsiveness to malaria sporozoite peptides. Correlation of effect with biologic activity of IL-2

Current malaria vaccine strategies focus on subunit vaccines that contain one or a limited number of malaria Ag. However, there is widespread nonresponsiveness to many of these Ag probably resulting from Ir gene control. Using a congenic mouse model, we demonstrated that human rIL-2 (as an adjuvant) can overcome Ir gene controlled low immune responsiveness to peptide malaria Ag vaccine candidates [R32tet32, R32LR, and Th2R-NP (NANP)5NA] as determined by the antibody response, providing it is emulsified with the Ag during immunization. This effect is not caused by IL-2 merely acting as a foreign protein and stimulating noncognate help; it requires biologic activity of the IL-2, as determined by studying the effect of inactive rIL-2, which has minimal biologic activity but which has retained its antigenicity. IL-2 does not appear to be working by an effect on priming of specific Th, and IL-2 cannot overcome an Ir gene controlled low T cell proliferative response. IL-2 may have a role to play in human vaccine development where a high titer antibody response to a subunit vaccine is required.     

Circulating levels of the interleukin (IL)-4 receptor and of IL-18 in patients with Plasmodium falciparum malaria

Circulating levels of sIL-4R, IL-18 and IFN-gamma were studied by ELISA in 36 Gabonese patients with Plasmodium falciparum malaria (29 children, 7 adults). Drug induced clearance of parasitemia, studied in 22 patients with mild disease, was accompanied by a rapid decrease of sIL-4R and IFN-gamma to normal values and an increase of circulating IL-18, suggesting the downregulation of a type 2 biased immune response and a dissociated type 1 responsiveness while resolving parasitemia. Comparing subgroups with hyperparasitemia/severe anemia and mild malaria, children with severe malaria had significant higher levels of sIL-4R and IFN-gamma, whereas IL-18 levels were not statistically different. Furthermore, among those children, higher levels of circulating IL-18 correlated with a lower degree of parasitemia.     

Cellular and humoral immune responses to Plasmodium falciparum gametocyte antigens in malaria-immune individuals. Limited response to the 48/45-kilodalton surface antigen does not appear to be due to MHC restriction

We have examined immune responses to a cultured Plasmodium falciparum gametocyte lysate and to an affinity-purified preparation of the 48/45-kDa gamete surface Ag in a group of 30 malaria immune individuals and in 24 Europeans with no previous exposure to malaria. Cellular responses were assessed in vitro by lymphoproliferation and production of IFN-gamma; antigamete antibodies were detected by immunofluorescence, Western blotting, and competitive ELISA. Cells from all the malaria immune donors responded to the gametocyte lysate in both assays while cells from nonimmune donors gave only weak proliferative responses. Antigamete antibodies were detected in the serum of all the immune donors but not in serum from nonimmunes. Nonimmune donors were completely unresponsive to the purified 48/45-kDa surface Ag while cells from 40% of immune donors responded by either proliferation or IFN-gamma production. Only 3 of 30 immune donors had detectable antibodies to the 48/45-kDa Ag. Class II HLA type was determined for 27 of the immune donors but no relationship between HLA-DR or -DQ and responsiveness to the 48/45-kDa Ag was discerned. The possible reasons for limited recognition of this gamete surface Ag are discussed.     

Antibodies and reactive T cells against the malaria heat-shock protein Pf72/Hsp70-1 and derived peptides in individuals continuously exposed to Plasmodium falciparum.

Pf72/Hsp70-1, a heat-shock protein of m.w. 72 kDa from Plasmodium falciparum is one of the Ag of interest to be included in a polyvalent vaccine against malaria. It is one of the major immunogens present in a fraction of purified blood stage parasites that elicited protection against experimental infection of Saimiri monkeys with blood stages of P. falciparum. It is present at all blood stages and one of its B cell epitopes is also detected on the surface of the infected hepatocyte. Moreover, Pf72 appears to be well conserved among different isolates of P. falciparum. We have examined the immune response against Pf72/Hsp70-1 in individuals from different age groups living in a holoendemic area (West Africa). The immune response against the native Ag (purified from schizonts and called Pf/Hsp70) was analyzed both at the humoral level by ELISA and at the cellular level by assessing in vitro proliferation and IFN-gamma production of PBMC. Of the individuals studied 52% had a statistically significant level of anti-Pf/Hsp70 antibodies as compared with unexposed individuals. These positive individuals showed a heterogeneous distribution because significant levels of antibodies were found in 70% of the adults but in only 26% of the children. The presence of Pf/Hsp70-specific reactive T cells in the blood was detected in 32% of the individuals. The total anti-Pf/Hsp70 antibody level (IgG+IgM) appeared strongly age related and correlated positively with parasite exposure, whereas the T cell response failed to correlate either with the antibody level or with age. Moreover, PBMC of donors responded to the Pf/Hsp70 in a dissociated way, namely, by either T cell proliferation or IFN-gamma production. Ten synthetic peptides based on sequences found in the C-terminal part of Pf72/Hsp70-1 were further tested as potential T cell epitopes. The proliferative response of PBMC from individuals continuously exposed to the parasite showed that three peptides more frequently trigger significant T cell proliferation (in 21% to 27% of the individuals) and three others less frequently (10%). None of these peptides allowed detection of reactive T cells in PBMC of Europeans with no previous exposure to malaria. Some of the stimulating peptides are highly similar to human heat-shock Hsc and Hsp70 with large stretches of identical amino acids.(ABSTRACT TRUNCATED AT 400 WORDS)     

The human immune response against the major merozoite surface antigen of Plasmodium falciparum.

The major surface antigen of the merozoite (MMSA) is very immunogenic in humans and it is considered a candidate for developing a malaria vaccine. This protein consists of conserved, dimorphic and polymorphic sequences that might differ in their ability to induce immunity. Epidemiological studies were undertaken in two different endemic areas of West Africa with the aim to identify the sequences within the protein that are the target of the humoral and cellular immune responses. Recombinant polypeptides expressed in E. coli, covering the conserved, the dimorphic and polymorphic regions, were used to evaluate the reactivity of sera and of Peripheral Blood Mononuclear Cells (PBMC) from inhabitants of rural communities exposed to P. falciparum transmission. The analysis of the humoral immune response against the MMSA showed that both qualitative and quantitative differences exist among groups of individuals with different susceptibility to P. falciparum infection. Furthermore, an association between intensity of transmission and antibody reactivity against the dimorphic regions was observed in individuals living in a malaria endemic area. The proliferative response of the PBMC was in most cases very low, however, several T cell clones could be established. The dimorphic region of MMSA was shown to contain T cell epitopes together with sequences most frequently recognized by human sera.     

Antigen-specific and MHC-restricted Plasmodium falciparum-induced human T lymphocyte clones

We established and analyzed human T lymphocyte clones induced by crude Plasmodium falciparum antigens of schizont-enriched asexual blood stages. Peripheral blood mononuclear cells (PBMC) were stimulated for 6 days with antigen, and the T cell blasts were separated and were transferred to limiting dilution cultures with antigen, irradiated PBMC, and recombinant interleukin 2. The following observations were made. Malaria antigen (M.Ag) induced similar proportions of T blasts in PBMC from infected individuals and noninfected controls, and the M.Ag-dependent clone frequencies (1/79 to 1/216) obtained with the blasts were similar. The majority of established clones derived from infected and noninfected subjects specifically recognized M.Ag and would not proliferate in response to red blood cells or autologous PBMC alone. They also required HLA class II determinant-compatible antigen-presenting (E-) cells. With three clones from one malaria patient, DR 1 or DR 5 specificities correlated with antigen presentation. Although T4+ and T8+ blasts were induced by M.Ag in PBMC, only T4 (Leu-3+) clones were obtained in our culture system. These clones secreted IL 2 in response to M.Ag. 4) Differential patterns of reactivity to native M.Ag, heat-stable antigens, and heat-precipitated antigens were exhibited by T cell clones, and the tested clones did not recognize Plasmodium berghei antigen. In conclusion, it is important with regard to previous observations on apparently nonspecific, mitogen-like effects of M.Ag in bulk T cell cultures that our results demonstrate specific recognition of P. falciparum by human T cells. The T cell clones obtained will be an important tool in the quest for a better understanding of the mechanisms involved in resistance to malaria infection.     

Novel mechanism for Trypanosoma cruzi-induced suppression of human lymphocytes. Inhibition of IL-2 receptor expression

Co-culture of blood forms of Trypanosoma cruzi, the causative agent of Chagas' disease, with human PBMC impaired the capacity of T lymphocytes to express surface receptors for IL-2. This effect was evidenced by marked reductions in both the proportion of Tac+ cells and the density of Tac Ag on the surface of the positive cells, determined by flow cytometry. The extent of the inhibition increased with parasite concentration. Under optimal or suboptimal conditions of stimulation with either PHA or monoclonal anti-CD3, specific for an epitope of the T3-Ti human T cell Ag receptor complex, the presence of T. cruzi curtailed the capacity of T lymphocytes to proliferate and express Il-2R but did not affect IL-2 production. Furthermore, the addition of exogenous IL-2 did not restore the responsiveness of suppressed human lymphocytes but did when mouse lymphocytes were used instead. Therefore, unlike mouse lymphocytes, human lymphocyte suppression by T. cruzi did not involve deficient IL-2 production and was accompanied by impaired IL-2 utilization. Co-culture of human monocytes/macrophages with suppressive concentrations of T. cruzi increased IL-1 production, and the parasite did not decrease IL-1 secretion stimulated by a bacterial LPS. Therefore, the suppression of IL-2R expression and lymphoproliferation is not likely to have been an indirect consequence of insufficient IL-1 production due to infection of monocytes or macrophages. We have shown that suppression of human lymphocyte proliferation by T. cruzi is not caused by nutrient consumption, absorption of IL-2, lymphocyte killing, or mitogen removal by the parasite. Therefore, these results uncover a novel suppressive mechanism induced by T. cruzi, involving inhibited expression of IL-2R after lymphocyte activation and rendering T cells unable to receive the IL-2 signal required for continuation of their cell cycle and mounting effective immune responses.     

The ability of peripheral blood mononuclear cells (PBMC) of syphilitic patients to produce IL-2

Abstract The cell-mediated immune response of importance in protection against Treponema pallidum , is distinctly suppressed in some stages of the disease. This may be a result of decreased ability of cells to produce IL-2, or IL-2 absorption by different factors. The experiments were designed to evaluate the ability of peripheral blood mononuclear cells (PBMC) of patients with different stages of syphilis to produce IL-2, and to investigate the causes which could possibly limit its activity. The ability of the PBMC of syphilitic patients to produce IL-2 develops at the beginning of the disease, reaching a maximum in primary seropositive syphilis. In the next stages of the disease this capability is distinctly lowered. The lowest was in malignant syphilis and tabes dorsalis, i.e. during severe disease. Absorption of adherent cells from PBMC increased the ability of lymphocytes to produce IL-2. The highest level of this interleukin was observed at the stages of the disease where suppression was the deepest. Sera of both control and syphilitic patients contained IL-2 inhibitor. Its level was the highest in early and late latent syphilis where no symptoms of disease were present. In all syphilitic sera a distinctly elevated level of soluble IL-2 receptors (sIL-2R) was also found. Its high level was noted in sera of patients in which PBMC had the weakest ability to produce IL-2. These findings suggest that sIL-2R may be bound to IL-2 and in this way would lead to weakening of T cell function and of resistance against Treponema pallidum infection.     

Human cord blood CD4+CD25hi regulatory T cells suppress prenatally acquired T cell responses to Plasmodium falciparum antigens

In malaria endemic regions, a fetus is often exposed in utero to Plasmodium falciparum blood-stage Ags. In some newborns, this can result in the induction of immune suppression. We have previously shown these modulated immune responses to persist postnatally, with a subsequent increase in a child's susceptibility to infection. To test the hypothesis that this immune suppression is partially mediated by malaria-specific regulatory T cells (T(regs)) in utero, cord blood mononuclear cells (CBMC) were obtained from 44 Kenyan newborns of women with and without malaria at delivery. CD4(+)CD25(lo) T cells and CD4(+)CD25(hi) FOXP3(+) cells (T(regs)) were enriched from CBMC. T(reg) frequency and HLA-DR expression on T(regs) were significantly greater for Kenyan as compared with North American CBMC (p < 0.01). CBMC/CD4(+) T cells cultured with P. falciparum blood-stage Ags induced production of IFN-γ, IL-13, IL-10, and/or IL-5 in 50% of samples. Partial depletion of CD25(hi) cells augmented the Ag-driven IFN-γ production in 69% of subjects with malaria-specific responses and revealed additional Ag-reactive lymphocytes in previously unresponsive individuals (n = 3). Addition of T(regs) to CD4(+)CD25(lo) cells suppressed spontaneous and malaria Ag-driven production of IFN-γ in a dose-dependent fashion, until production was completely inhibited in most subjects. In contrast, T(regs) only partially suppressed malaria-induced Th2 cytokines. IL-10 or TGF-β did not mediate this suppression. Thus, prenatal exposure to malaria blood-stage Ags induces T(regs) that primarily suppress Th1-type recall responses to P. falciparum blood-stage Ags. Persistence of these T(regs) postnatally could modify a child's susceptibility to malaria infection and disease.     

Differential expression and tissue compartmentalization of the inflammatory response following thermal injury

Studies have shown that both animal tissue-fixed immune cells and human peripheral blood mononuclear cell (PBMC) functions are altered after burn injury. Additional studies suggest that the burn injury-induced alterations in these divergent cell populations from different species are similar. It remains unknown, however, whether the observed changes in animal tissue-fixed immune cell function following thermal injury also occurs to a similar extent in the PBMC population. The aim of our study was to compare PBMC and tissue-fixed immune cell functions from the same animal using a murine burn model. At 7 days post-burn, mice were more susceptible to sepsis and delayed type hypersensitivity responses were suppressed. Splenocytes isolated from injured mice displayed suppressed proliferation and increased IL-10 production. In contrast, PBMC from injured mice displayed suppressed proliferation, IL-2 and IFN-gamma production. Splenic macrophage nitric oxide, PGE(2), TNF-alpha, IL-6 and IL-10 production was enhanced post-burn and IL-12 production was suppressed. PBMC from such animals displayed enhanced PGE(2) production and suppressed IL-6 and IL-12 production. These results indicate that while an immunosuppressive Th(2) phenotype (increased IL-10 and/or suppressed IL-2, IFN-gamma) was induced in both the splenic and PBMC compartments post-injury, differential expression and dimorphism in the response also exists. Thus, the assessment of only PBMC function in burn patients may not accurately reflect the patient's actual immune status at the tissue level.