Immune responses during human Schistosomiasis mansoni. XI. Immunologic status of patients with acute infections and after treatment

Sixteen patients, 8 to 30 yr of age, with acute (toxemic) phase schistosomiasis mansoni were studied immunologically within 2 to 3 mo of their exposure to Schistosoma mansoni cercariae, and were monitored after chemotherapy. Total leukocyte levels and peripheral blood eosinophilias were higher in these patients than in similar individuals with chronic schistosomiasis mansoni. In contrast to chronic patients, the eosinophilias of the acute cases were decreased rather than elevated upon treatment. Total lymphocyte population (T and B cell) percentages were not altered during acute infection. Lymphoid subset (T3+, T4+, and T8+) analysis revealed elevated levels of both T4+ and T8+ cells. In vitro blastogenic responses of peripheral blood mononuclear cells (PBMN) to heterogeneous schistosome-derived antigens (eggs, SEA; adult worms, AW; and cercariae, CERC) were evaluated. SEA responsiveness was considerably higher than that of patients with chronic S. mansoni infections. The ratios of SEA to AW responses in acute cases gave a mean of 2.0, as opposed to 0.5 for a comparable group of chronically infected patients. The sera of most acute patients already contained suppressive factors that specifically decreased schistosomal antigen-induced PBMN blastogenesis. Chemotherapy of acute cases lead to a diminution of PBMN responsiveness to SEA and CERC. Treatment of patients with chronic infections lead to the elevation of such responses. PBMN from patients with acute infections produced lymphokine leukocyte inhibition factor upon exposure of the cells to SEA but not AW. A similar pattern was true for production of the lymphokine activity mitogenic factor. Levels of antibody in sera of acutely infected patients against SEA, CERC, and AW were considerably higher than levels in sera of chronically infected patients matched for age and intensity of their infections. These high antibody titers persisted for at least 6 mo after treatment, and were unrelated to the intensity of infection. The immunologic status of these patients with acute schistosomiasis mansoni differed considerably from patients with chronic infections. These findings re-emphasize the immunoregulatory events that apparently develop upon continued exposure to schistosomes and their products during chronic infection.     

Macrophages as effector cells of protective immunity in murine schistosomiasis. VI. T cell-dependent, lymphokine-mediated, activation of macrophages in response to Schistosoma mansoni antigens

Macrophages from Schistosoma mansoni-infected mice kill significant numbers of skin stage schistosomula and murine fibrosarcoma cells in vitro. In order to determine whether the macrophage tumoricidal and larvicidal activation observed in mice as a result of S. mansoni infection are mediated through T cell-dependent (lymphokine) or B cell-dependent (antibody or immune complex) mechanisms, the development of macrophage populations with cytotoxic activity against schistosome larvae or tumor cells was monitored in S. mansoni-infected nude or mu-suppressed mice. Whereas peritoneal cells from S. mansoni-infected congenitally athymic mice had no activity in either assay, cells from mu-suppressed S. mansoni-infected mice showed cytotoxic activity equivalent to that of cells from untreated S. mansoni-infected counterparts. Cells from mu-suppressed uninfected mice were not activated. The mu-suppressed animals had no detectable nonspecific IgM or specific antischistosome IgM, IgG, or IgE antibodies and showed a 90% reduction in numbers of splenic IgM+ cells upon fluorescence activated cell sorter analysis. These results indicate that antibody is not required for in vivo activation of macrophages during S. mansoni infection. Further experiments showed that lymphoid cells from S. mansoni infected mice respond in culture with various specific antigens (such as living or dead whole schistosomula or soluble adult worm antigens) by production of factors capable of activating macrophages from uninfected control mice to kill schistosomula or tumor cells in vitro. Macrophage-activating factors were produced by T cell-enriched, but not T cell-depleted or B cell-enriched, populations from spleens of schistosome-infected mice in response to schistosome antigen. Similar lymphokines may be responsible for the macrophage activation observed during chronic murine schistosomiasis. These observations emphasize the potential contribution of T cell-mediated immune mechanisms in resistance to S. mansoni infection.     

In vitro delayed hypersensitivity granuloma formation: development of an antigen-coated bead model

Previously, we have described an in vitro model of granulomatous hypersensitivity around Schistosoma mansoni eggs in both the murine model of schistosomiasis and in human schistosomiasis. These studies describe a new model of in vitro granuloma formation that complexes soluble egg antigen from S. mansoni eggs, a partially purified protein derivative of Mycobacterium tuberculosis (PPD), or bovine serum albumin to carrier beads. Ultrastructural and morphologic evaluations demonstrate that there are initial macrophage interactions, followed by the recruitment of antigen-specific T cells that interact with and recruit macrophages, lymphocytes, granulocytes, and fibroblasts. Finally, there is a stage of granulomatous organization involving fibroblast proliferation and collagen deposition. The in vitro reactivity, defined by a quantitative granuloma index, correlates with in vivo granulomas around S. mansoni eggs in the livers of infected cell donor animals. In vitro granuloma formation against PPD-coated beads correlated with delayed cutaneous hypersensitivity against PPD, which was judged by footpad swelling. The reactions demonstrate antigenic specificity and were intrinsically modulated in a manner that is analogous to that previously shown with the in vitro egg granuloma model. This model of in vitro granuloma formation promises to be a useful tool for elucidating mechanisms of cellular immunity and regulation.     

Model of in vitro granulomatous hypersensitivity in human paracoccidioidomycosis

With the purpose of studying the immunological components of granulomatous hypersensitivity in patients infecteded with Paracoccidioides brasiliensis, we used the model of in vitro granuloma formation developed for schistosomiasis studies, that correlates with in vivo granulomatous reactivity occurring around eggs trapped in organs of infected donors. In this case, granuloma formation can be determined examining cellular reactivity manifested as multiple cell layers surrounding antigen-conjugated polyacrilamide beads. Our results showed that peripheral blood mononuclear cells (PBMC) obtained from acute treated and chronic paracoccidioidomycosis patients proliferate and generate in vitro granulomas in response to P. brasiliensis antigens (PbAg). In contrast, no proliferation or granuloma formation were observed when PBMC from acute non-treated patients were used. These studies demonstrate the feasibility of investigating granulomatous hypersensitivity in P. brasiliensis-infected patients by using an in vitro granuloma model. This revised version was published online in June 2006 with corrections to the Cover Date.     

Characterization of Schistosoma mansoni antigen-reactive T cell clones that form granulomas in vitro

Granuloma formation and modulation in schistosomiasis are a consequence of discrete subpopulations of T lymphocytes and the mediators they produce. In the present study, T cell clones reactive to soluble egg antigen (SEA) were developed to analyze the roles of T cells in Schistosoma mansoni egg-induced granuloma formation. In an in vitro granuloma assay, 1 X 10(5) T cells specifically augmented the response of 2 X 10(6) normal spleen cells to SEA-coupled but not purified protein derivative-coupled polyacrylamide beads. In vitro granulomatous responses by individual clones were correlated with their capacity to mediate local delayed-type hypersensitivity reactions in footpad swelling assays. Phenotypic analysis of the seven clones characterized in the present study demonstrated that they were L3T4+, Ly-2.2-. An analysis of supernatants of T cells pulsed with concanavalin A or SEA + antigen-presenting cells was also undertaken in an attempt to correlate in vitro granuloma formation with lymphokine production. Stimulated T cells (but not unstimulated T cells) produced interleukin 2, macrophage activating factor, migration inhibitory factor, and eosinophil stimulation promoter in response to both mitogenic and antigenic stimuli. The results suggest that individual clones of T cells are capable of producing a variety of mediators that influence their ability to activate and to recruit cells into granuloma formation. The model may be useful in the analysis of specific antigens and regulatory interactions and their contribution to granuloma formation.     

Egg deposition is the major stimulus for the production of Th2 cytokines in murine schistosomiasis mansoni.

To characterize Th cell populations induced by helminth infection, spleen cells from mice infected with Schistosoma mansoni were stimulated with parasite (worm or egg Ag) or mitogen (Con A) and the supernatants assayed for the Th1-specific cytokines IFN-gamma and IL-2 and the Th2-specific cytokines IL-4 and IL-5. Th2 cytokine production was not detected in substantial quantity until the 6 to 8th wk of infection and after reaching peak levels at 8 to 12 wk declined slowly thereafter. The time courses of IL-4 and IL-5 production, whereas differing from each other, closely resembled corresponding published data on IgE and peripheral blood eosinophil levels during murine schistosome infection. In contrast, Th1 cytokine responses occurred only during the first 6 wk of infection and were virtually absent during the peak period of Th2 production. To assess the role of egg deposition in the observed pattern of Th response, cytokine production was assayed in mice carrying unisexual schistosome infections in which parasite eggs are absent. Splenocytes from these animals displayed only marginal Th2 cytokine synthesis but greater Th1 cytokine responses than the corresponding cells from mice with bisexual infections. Moreover, cultures of liver tissue or isolated granulomas from infected mice constitutively produced high levels of IL-4 and IL-5 but failed to synthesize significant amounts of IL-2 and IFN-gamma even when stimulated with egg Ag or mitogen. Taken together the data indicate that egg deposition is the major stimulus of Th2 cytokine response in S. mansoni-infected mice and suggest that T cells belonging to this subset must play a major role in egg granuloma formation.     

Immune response against protozoal and nematodal infection in mice with underlying Schistosoma mansoni infection

Schistosoma mansoni infection induces T helper (Th) 2-dominant immune response in mice not only to S. mansoni itself but also to other coexisting antigens. In the present study, we challenged S. mansoni-infected mice with the intestinal nematode, Strongyloides venezuelensis, and the intracellular protozoa, Leishmania major to see whether such Th2-dominant immune responses alter susceptibility of the host to other concomitant parasitic infections. The recovery of S. venezuelensis adult worms from the small intestine was significantly decreased by S. mansoni infection, and the protection to S. venezuelensis appeared to act on migrating larvae. Antibodies elicited by S. mansoni infection showed cross-binding to third-stage larvae antigen of S. venezuelensis. On the other hand, S. mansoni infection did not affect the outcome of L. major infection in both susceptible BALB/c and resistant C57BL/6 mice. Popliteal lymph node cells of BALB/c mice expressed mRNA for interleukin (IL)-10 rather than IL-4, regardless of S. mansoni infection, and those of C57BL/6 mice expressed IFN-gamma mRNA upon L. major antigen stimulation, even in S. mansoni-infected mice. Our findings suggest that Th2-dominant immune response induced by S. mansoni protects mice from intestinal helminthic infections, whereas they do not always modulate protozoal infections.     

The substance P receptor is necessary for a normal granulomatous response in murine schistosomiasis mansoni

Immune cells within the granulomas of murine schistosomiasis mansoni make the neuropeptide substance P (SP) and express neurokine 1 receptor, which is the specific receptor for substance P (SPr). It was determined if mice with deletion of the SPr (SPr-/-) would develop a normal granulomatous response to schistosome ova during the course of natural infection. Mean liver granuloma size was smaller in SPr-/- mice compared with that of wild-type control animals. Although flow analysis revealed little difference in the cellular composition of the granulomas, both splenocytes and granuloma cells from SPr-/- mice produced much less IFN-gamma and IgG2a and less IgE. The expression of Th2 cytokines (IL-4/IL-5) and IgG1 was comparable to the wild-type control. The mouse with targeted disruption of its SPr had the nonmammalian gene encoding the enzyme beta-galactosidase inserted in exon 1 of the SPr gene. There was beta-galactosidase activity in many mononuclear cells scattered throughout the schistosome granulomas of SPr-/- mice. Also, a granuloma T cell line derived from this transgenic mouse produced beta-galactosidase. These results provide further evidence that in murine schistosomiasis SPr is displayed commonly on granuloma inflammatory cells and is important for granuloma development and expression of IFN-gamma circuitry in this natural infection.     

Evidence of altered secondary lymphoid-tissue chemokine responsiveness in Balb/c mice infected with Schistosoma mansoni

To determine the extent to which splenic T cells were affected by Schistosoma mansoni infection, we investigated the ability of the T cells to produce interferon (IFN)-gamma, as well as their chemotactic ability 7 wk PI. In this study, we report that splenic T cells from Balb/c mice with S. mansoni infections were capable of producing levels of IFN-gamma comparable with splenic T cells from naive mice. However, the T cells exhibited altered chemotactic activity, as evidenced by an inability to respond to secondary lymphoid-tissue chemokine (SLC/CCL21). Although no difference in chemokine expression was found between the spleens of infected versus control mice, chemokine production was greater in the livers of infected versus control mice. Collectively, these data indicate that Balb/c mice with 7-wk S. mansoni infection possess splenic T cells with altered chemotactic activity and that the alterations may be a consequence of the granulomatous response in the liver.     

Schistosoma mansoni antigens alter the cytokine response in vitro during cutaneous leishmaniasis

Schistosoma mansoni infection or associated products are able to down-modulate the type 1 CD4+ T cell inflammatory response characteristic of autoimmune diseases. In this study, we evaluated how S. mansoni antigens altered the immune response that was induced by the soluble Leishmania antigen (SLA) from cutaneous leishmaniasis (CL) patients. Cytokines were measured from the supernatants of peripheral blood mononuclear cell cultures stimulated with SLA. This was performed using the sandwich enzyme linked immunosorbent assay technique in the presence or absence of S. mansoni recombinant antigens Sm29, SmTSP-2 and PIII. The addition of S. mansoni antigens to the cultures resulted in the reduction of interferon gamma (IFN-γ) levels in 37-50% of patients. Although to a lesser extent, the antigens were also able to decrease the production of tumour necrosis factor-alpha (TNF-α). We compared patients that either had or did not have reduction in IFN-γ and TNF-α production in cultures stimulated with SLA in the presence of S. mansoni antigens. We found that there was no significant difference in the levels of interleukin (IL)-10 and IL-5 in response to S. mansoni antigens between the groups. The antigens used in this study down-modulated the in vitro proinflammatory response induced by SLA in a group of CL patients through a currently undefined mechanism.     

Attempts to manipulate specific responses to induce resistance to Schistosoma mansoni in Kenyan baboons (Papio anubis)

Attempts were made to manipulate specific responses of baboons to protect them from infection with Schistosoma mansoni. In Experiment 1, eosinophilia was induced in naive baboons with Trichinella spiralis larvae given intravenously before intraperitoneal injection of globulin fractions from S. mansoni-infected baboon sera and subsequent percutaneous exposure to S. mansoni cercariae. In Experiment 2, baboons with 8- or 32-week-old primary S. mansoni infections received T. spiralis i.v. before an S. mansoni challenge. In experiments 3 to 5 respectively, naive baboons received intramuscularly before challenge: formalin-fixed S. mansoni schistosomula, with Bordetella pertussis as an adjuvant; a preparation of S. mansoni adult worm teguments; and a preparation of IgE-immune complexes obtained from S. mansoni-infected rat sera, with Freunds Complete Adjuvant. Minor, but statistically insignificant, protection was obtained in Experiments 2 (32-week infections) and 3, but was far less than that given by intact, irradiated living vaccines. There are signs on the horizon of non-living vaccines protecting rodents against S. mansoni infection and it would be prudent, as with drugs, to test these in primates before proceeding to man. The results of our experiments, though essentially negative, should help the design of any future vaccine trials in primates.     

Modulation of eosinophil cytotoxicity by blood mononuclear cells from healthy subjects and patients with chronic schistosomiasis mansoni

Human blood mononuclear cells in culture release a factor(s) that markedly enhances eosinophil cytotoxicity. This factor(s) stimulates eosinophils to kill Schistosoma mansoni larvae at low antibody concentrations and cell/target ratios. A study of the mononuclear cells of 78 subjects with chronic schistosomiasis mansoni and 33 controls suggests that the production of eosinophil cytotoxicity enhancing activity (ECEA) is suppressed in most patients with S. mansoni infections. Suppression of ECEA production was not observed, however, with cells from many patients with heavy infections, including patients with hepatosplenomegaly. The possible role of ECEA in the development of pathology is discussed.     

Production of the lymphokine soluble immune response suppressor (SIRS) during chronic experimental schistosomiasis mansoni

Chronic schistosomiasis mansoni is a helminthic infection characterized by cell-mediated anti-egg granulomatous reactions and a variety of associated immunoregulatory phenomena. Soluble immune response suppressor (SIRS) is a lymphokine produced by activated suppressor T lymphocytes in various experimental settings. This report demonstrates the presence of SIRS in the sera of mice with chronic schistosomiasis mansoni (at least 20 wk of infection), but not in the sera of mice with earlier infections. Also, cultures of isolated, intact, hepatic, egg-focused granulomas from chronically infected mice released detectable levels of SIRS. These are the immunomodulated lesions characteristic of this infection. Large, intense, unmodulated granulomas obtained from acutely infected mice did not release SIRS. There is, therefore, a strong association between the presence of SIRS in the serum, the production of SIRS by intact lesions, and the chronic, immunomodulated stage of schistosomiasis mansoni.     

Enhanced UVfemale1 tumor growth in CBF1 mice infected with Schistosoma mansoni due to modulation of Th1-like responses

Effects of Schistosoma mansoni infection on anti-tumor immunity were examined in CBF1 mice with ultraviolet-induced UVfemale1 fibrosarcoma cells. Although many laboratory established tumor cells had rejection mechanisms independent of CD4(+) T cells, we confirmed that CD4(+) cells had significant roles in rejection of UVfemale1 cells in the syngeneic CBF1 mice. When we prepared two CBF1 mouse groups, S. mansoni-infected and schistosome-free, the former group showed up-regulation of Th2-like response to UVfemale1 cells, whereas the latter group mice showed rather type 1-dominant patterns. Cytotoxic activity against UVfemale1 cells tested in vitro, which was attributed to CD8(+) cells, was significantly weaker in S. mansoni-infected mice compared with infection-free mice. In tumor challenge experiments in vivo, we observed that rapid and complete rejection of UVfemale1 cells required the presence of CD8(+) T cells. Under only CD4-depleted situation, survival of tumor cells in schistosome-free mice was prolonged up to 1 month or more. Under the presence of both CD4(+) and CD8(+) cells, S. mansoni infected mice rejected the challenged UVfemale1 cells as was seen in normal mice. However, when CD8(+) cells were depleted from S. mansoni-infected mice, inoculated UVfemale1 cells grew more rapidly than in infection-free mice. Our results suggest that functionally polarized cytokine patterns in schistosome-infected hosts promote rapid tumor growth.     

Modulation of granulomatous hypersensitivity. I. Characterization of T lymphocytes involved in the adoptive suppression of granuloma formation in Schistosoma mansoni-infected mice.

The cellular basis of the spontaneous modulation of the granulomatous response to schistosome eggs was analyzed in mice infected with Schistosoma mansoni. Spleen cells of 20 or 32 week-infected mice undergoing modulation, when transferred to 6 week-infected recipients, suppressed the maximal granulomatous response at 8 weeks. Suppression of both naturally forming asynchronous liver and synchronously induced lung lesions was achieved. Specificity of this effect was demonstrated by the suppression of egg granulomas but not antigen-coated bead granulomas developing simultaneously in the lungs of cell recipients. Further characterization showed that suppression was abrogated by pretreating transferred cells with either anti-Thy 1.2 or anti-Iak alloantisera and C. Transfer of macrophage-depleted or fractionated T and B spleen cells confirmed that T cells alone transferred suppression. Moreover, an Ia antigen-bearing (Ia+) subpopulation of T cells was required in the transferred suppression. Moreover, an Ia antigen-bearing (Ia+) subpopulation of T cells was required in the transferred population. An examination of T cells obtained from isolated, dispersed lung granulomas from control and adoptively suppressed mice revealed an increased proportion of Ia+ cells in the latter. It is suggested that Ia+ T cells may be involved in the local modulation of the granulomatous response.     

Suppression of natural killer cytolytic activity in mice undergoing pulmonary granulomatous inflammation

CBA/J mice undergoing pulmonary granulomatous inflammation exhibited depressed NK cytolytic activity. Granulomas induced by i.v. embolization of Schistosoma mansoni eggs (hypersensitivity type) or Sephadex beads (foreign body type) both caused reduced NK activity, although hypersensitivity granulomas induced a significantly higher level of NK suppression. Kinetic analysis of hypersensitivity lesions at 4, 8, 16, and 32 days post-embolization indicated that NK activity was significantly suppressed by day 8, maximally suppressed by day 16 (at the peak of the inflammatory response) then returned to near control values by day 32 (as the granulomas resolved). Suppression of NK activity ranged from three- to 15-fold in different experiments. NK cells obtained from both spleen and peripheral blood demonstrated reduced NK activity with kinetic patterns similar to the granuloma NK cells. Suppression was not due to reduced splenic NK cells as the frequency of YAC-1 binding cells, as well as asialo GM1+ or laminin+ cells remained constant over the entire study period. Suppression of NK activity did not appear to be due to serum components or suppressor cells present in the spleen preparations. However, the suppression of NK activity could be reversed by overnight incubation of spleen cells at 25 or 37 degrees C or daily treatment of the mice with indomethacin. Suppression also appeared relatively specific for NK cells as the generation and expression of cytotoxic T lymphocyte activity was not affected.     

Role of IL-4 and IFN-gamma in Schistosoma mansoni egg-induced hypersensitivity granuloma formation. Orchestration, relative contribution, and relationship to macrophage function.

A well defined model of T cell-mediated hypersensitivity-type granulomatous inflammation induced by Schistosoma mansoni eggs was used to assess the role of IL-4 and IFN-gamma in granuloma development. Synchronized pulmonary granulomas were induced and isolated from S. mansoni-infected mice during vigorous (8 wk) and modulated (20 wk) stages of the disease. The sequential production of IL-4 and IFN was determined and related to temporal changes in granuloma macrophage production of IL-1, TNF, and superoxide anion (O2-). During the vigorous stage, IL-4 was produced on days 1 and 2 of granuloma formation, whereas IFN was released in greatest amounts on days 4 to 8. The peak of IL-4 occurred in a window between the peak of IL-1 (1 day) and maximal TNF production (8 to 16 days). Maximal O2- release tended to parallel IFN production. During the modulated stage when the inflammatory response is attenuated, IL-4 production was dramatically reduced as were levels of IL-1 and TNF, but IFN production persisted and maximum O2(-)-producing capacity was only delayed in onset. mAb specific for IL-4 and IFN were used to examine the effect of in vivo depletion of these cytokines on granuloma development. Administration of a single 1.0-mg dose of anti-IL-4 antibodies to mice with synchronously developing granulomas dramatically reduced granuloma size (40 to 50% suppression of area) during an 8-day study period, whereas antibodies to IFN had no effect on size. However, the latter treatment reduced giant cell formation. Our results indicate that granuloma development involves an orchestrated production of cytokines possibly resulting from sequential participation of different Th cell populations. Moreover, IL-4 is a pivotal cytokine in anamnestic cellular recruitment and subject to endogenous regulation.     

Role of oxygen reactive species in Schistosoma mansoni egg-induced granulomatous inflammation

The role of oxygen reactive species in granulomatous hypersensitivity was explored using a model of pulmonary granulomas induced by intravenous injection of eggs from the parasite Schistosoma mansoni. Macrophages from sychronously developing lesions spontaneously released significant quantities of superoxide anion (26 nmoles/10(6)/2h) by 8 days of development. In contrast, the non-T cell foreign body (Sephadex bead) granuloma macrophages produced only (2 nmoles/10(6)/2h) small quantities. Daily administration of the oxygen scavenger, alpha-tocopherol, by either oral or parenteral routes caused up to 60% suppression of granuloma size. Moreover, parenteral administration of specific inactivators of 0-2 and H2O2, superoxide dismutase and catalase respectively, resulted in a 30 to 40% reduction in granuloma size. These data suggest that oxygen reactive species take part in the generation of hypersensitivity granulomas.     

Immune responses during human schistosomiasis mansoni. VI. In vitro nonspecific suppression of phytohemagglutinin responsiveness induced by exposure to certain schistosomal preparations.

Simultaneous in vitro exposure of human peripheral blood mononuclear cells to phytohemagglutinin-P (PHA) and either soluble schistosomal egg antigenic preparation (SEA) or soluble cercarial antigenic preparation (CAP) obtained from Schistosoma mansoni resulted in decreased responsiveness as compared to exposure to PHA alone. The addition of a soluble adult worm antigenic preparation (SWAP) did not predictably alter PHA responses in this system. The suppression due to in vitro exposure to either SEA or CAP was expressed whether the lymphocyte donors were S. mansoni patients (early infection, chronic, or treated), or uninfected subjects. The degree of suppression was related to the concentration of SEA used, and the timing of exposure. Preexposure to SEA for 3 days before the addition of PHA resulted in more potent suppression. However, a delay in the time of the addition of SEA of 6 and 24 hr after PHA exposure decreased and eliminated, respectively, its suppressive capacity. SEA and CAP were not directly toxic to responding cells, and appeared to exert their nonspecific suppressive influences through T lymphocyte-related mechanisms. It was observed that although these suppressive events could be induced and observed in vitro, the responsiveness of S. mansoni patient lymphocytes to PHA was equal with that of uninfected controls.     

Natural anti-bacterial activity against Salmonella typhi by human T4+ lymphocytes armed with IgA antibodies

Peripheral blood mononuclear cells from normal volunteers possess natural anti-bacterial (NA) activity against S. typhi that can be measured in a 2-hr in vitro assay. Employing fractionation on nylon wool columns, Percoll gradients, plastic adherence, and E rosetting, the effector cell of NA activity appeared to be a lymphocyte of the T lineage rather than a macrophage, a B lymphocyte, or a large granular cell. Moreover, complement-dependent killing with monoclonal antibodies such as OKM1, OKB7, OKT8, 5.9 and the anti-natural killer cells AB8.28 did not reduce NA activity. On the contrary, this was completely inhibited when OKT3, OKT11, or OKT4 antibodies and complement were used to pretreat the effector lymphocytes. Indeed, T4+ cells sorted with a FACS displayed an extremely high NA activity against S. typhi. By pretreatment of peripheral lymphocytes with F(ab')2 fragments against human IgA, the NA activity was blocked. It is therefore suggested that NA activity by human cells might be a mechanism of defense against infections, acting as antibody-dependent cellular cytotoxicity expressed by T4+ lymphocytes coated with preexisting anti-Salmonella IgA antibodies.