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Visceral leishmaniasis, caused by Leishmania donovani, is a chronic disease with a high mortality rate. This protozoan induces a serious dysfunction of the immune system characterized by suppression of the cellular response to parasite antigens. We provide evidence for the involvement of lipids in the immunological alterations of experimental leishmaniasis. Sera obtained from 60-day-infected hamsters present increased triglyceride levels. Inhibition of cell proliferation was observed when splenocytes from normal hamsters were stimulated with concanavalin A in the presence of 3% infected hamster serum (IHS) (Control 50 +/- 3 (x10(3)) cpm; IHS 5 +/- 1 (x10(3)) cpm). This inhibition was reversed by the addition of 5 mg/ml of delipidated bovine serum albumin (BSA) to the cultures (Control 65 +/- 1 (x10(3)) cpm; IHS 75 +/- 3 (x10(3)) cpm). The inhibitory effect of IHS was demonstrable only when added to the culture simultaneously with the mitogen. This effect was not as intense on fresh, pre-activated cells or on the CTLL-2 cells. This cell line stimulated by IL-2 in the presence of IHS is only marginally inhibited (about 20% inhibition). The suppressor effect on CTLL-2 was not reversed by the addition of increasing doses of IL-2 (up to 100 U/ml) to cultures. The inhibition of the proliferative response of the CTLL-2 cells caused by IHS was also reversed by the addition of delipidated BSA. Our data suggest a role for fatty acids in the infected hamster serum-induced suppression of normal or L. donovani-infected cell proliferation.

Cyclophosphamide (Cy) has been shown to modulate antibody responses in a wide range of diseases both in humans and experimental animals. Our results in Syrian hamsters infected with Leishmania donovani have shown that Cy blocks specific and polyclonal antibody production both in vivo and in vitro. This effect was achieved by weekly 100 mg/kg doses and also by a 300 mg/kg single dose. Although Cy provokes a significant decrease in B-cell numbers in infected animals, this cannot explain the suppression of antibody production since a 50% decrease in B-cells of only-infected hamsters did not reproduce the same effect in in vitro assays. Also, this suppression was not reversed either by elimination of adherent cells or by the presence of indomethacin. These data suggest that Cy affects T-cell populations involved in the control of antibody production by B-cells.

We observed histopathological and ultrastructural hepatic changes following the intracardiac inoculation of Leishmania donovani amastigotes into inbred LHC hamsters (group I). Since granuloma formation is known to be T-cell-dependent, we also examined infected hamsters under cyclophosphamide immunosuppressive treatment (group ICy) and evaluated the production of interleukin-2 (IL-2) by their cells. Group I showed more intense hepatocyte and endothelial cell clasmatosis as well as hepatocyte degeneration and necrosis, deposits of connective tissue fibers, granulomas with multinucleated giant cells (MGCs) of foreign-body and Langhans' types and reduced production of IL-2 by spleen cells. In contrast, group ICy hamsters exhibited larger eosinophil and lymphocyte populations within sinusoids and peri-sinusoidal areas but showed no MGCs in granulomas. A striking decline in IL-2 production was noted. These results suggest that cyclophosphamide induces a delay in the natural evolution of L. donovani-induced granulomatous hepatic inflammation.

Studies were carried out on the mechanisms by which B lymphocytes are polyclonally activated to secrete antibodies during visceral leishmaniasis. Crude extracts of Leishmania donovani, the aetiological agent of this disease, of Leishmania mexicana amazonensis, the etiological agent of cutaneous leishmaniasis, and of Herpetomonas muscarum, a related non-pathogenic organism, all contain components which cause strong in vitro polyclonal activation of hamster spleen cells leading to the production of antibodies. However, in vivo, only hamsters infected with L. donovani develop hypergammaglobulinaemia due to B cell polyclonal activation. Hamsters injected with the crude extracts of leishmania or infected with L. mexicana amazonensis do not manifest these alterations in their B cell response. Furthermore spleen cells of hamsters infected with L. donovani became unresponsive to stimulation with the T cell mitogen phytohaemagglutinin (PHA) by day 10 of infection, whereas their response to concanavalin A (Con A) was preserved. The decreased lymphocyte response to PHA coincided with the augmentation of the PFC/spleen ratio. In contrast, spleen cells from hamsters infected with L. mexicana amazonensis, responded normally to both mitogens throughout the course of infection. These results suggest that the hypergammaglobulinaemia present in visceral leishmaniasis may be the consequence of an inbalance of regulatory T cells, possibly associated with a direct stimulation of hamster B cells by L. donovani components.

This study provides biochemical and electron spin resonance spectroscopic evidence that contract of human polymorphonuclear leukocytes with antibody-coated Trypanosoma cruzi triggers the respiratory burst. Oxygen consumption, superoxide anion and hydrogen peroxide release were stimulated under conditions of polymorphonuclear leukocyte-mediated killing. This stimulation did not occur under non-killing conditions when antibody was omitted. A common mechanism of cytotoxicity of human polymorphonuclear leukocytes against different T. cruzi forms is suggested by the triggering of the respiratory burst by antibody-coated epimastigotes and trypomastigotes.

Skin-test were performed in 226 students, 12 to 14 years old, in a Rio de Janeiro elementary school using PPD-Rt23, PPD-G210 and PPD-B. The differential tuberculin test using these three antigens showed that 24,3% of the children presented a stronger reaction for non-tuberculous mycobacterial tuberculins than to PPD-Rt23, suggesting that infections with such organisms may occur. A high proportion (74,5%) showed the strongest reaction with PPD-G210 and probably this antigen is the most interesting to be used simultaneously with PPD-Rt23. Children with the largest tuberculin reaction to PPD-Rt23 represented 27,4% of the total. This group consists of individuals who have had a tuberculous infection. The third group (48,3%) provided evidence for a heterogeneous sensitization with the tubercle bacillus and at least one atypical mycobacteria.

226 students of both sexes from 12 to 14 years old were examined for tuberculin hypersensitivity with PPD-Rt 23 and PPD-T antigens. Strong reactions (greater than or equal to 10 mm diameter) were noted in 25,2 and 23,5% of the population, respectively. Individuals showing a weak or no reaction to PPD-Rt 23 had a weaker reaction to PPD-T, but those with a strong reaction to PPD-Rt 23 had an equivalent reaction with PPD-T.

The antibody-dependent cellular cytotoxicity activity of normal human blood cells against epimastigotes of Trypanosoma cruzi was measured by the release of incorporated [3H]uridine. Sera from patients with chronic Chagas' disease were used to sensitize the parasites to the lytic activity of the effector cells. Different steps of peripheral blood cell purification were employed, and different cell subpopulations were tested as effectors in the system. The main cytotoxic activity was detected in the granulocyte-rich fraction.

We have investigated the nature of the ligand involved in antibody-dependent cellular cytotoxicity (ADCC) of human leukocytes to epimastigotes of Trypanosoma cruzi. Purified anti-T. cruzi IgG was highly efficient in mediating ADCC whereas IgM mediated the killing of this parasite poorly even at high concentrations. The presence of the Fc portion on the IgG molecule seems to be necessary since F(ab')2 derived from anti-T. cruzi IgG did not mediate ADCC. We also present evidence suggesting that the mediator, aside from promoting the interaction between the effector and target cells, may play a functional role in triggering target destructions by the effector cells. This conclusion is based on results of experiments in which lectins capable of binding to both leukocytes and parasite were used as mediators of cellular cytotoxicity. The lectin concanavalin A could readily replace IgG for human leukocyte killing of T. cruzi. In contrast, lectins from Lens culinaris, Triticum vulgaris, Aaptos papillata and Bandeirae simplicifolia although capable of interacting with leukocytes and T. cruzi, did not mediate the cellular cytotoxicity of the parasites. The specific cellular mechanism of parasite killing, i.e. phagocytosis and or extracellular lysis, remains to be determined.