Enhancement of delayed-type hypersensitivity to Trypanosoma cruzi in mice treated with Mycobacterium bovis BCG and cyclophosphamide

Saponin adjuvant primes for a dominant interleukin-10 production to ovalbumin and to Trypanosoma cruzi antigen

The adjuvant activity of saponin for T-cell responses was evaluated and compared with that of complete Freund's adjuvant (CFA) in two antigen systems: a lysate of the protozoa Trypanosoma cruzi and ovalbumin (OA). Strong delayed-type hypersensitivity and T-cell proliferate responses, comparable with those stimulated by CFA, were observed for both antigens following immunization with saponin as adjuvant. Upon in vitro secondary antigen stimulation, high interleukin-10 (IL-10) and low interferon-gamma (IFN-gamma) levels were observed in lymph node (LN) cell cultures from saponin-immunized mice in contrast with the high IFN-gamma and decreased IL-10 production by LN cells from CFA-immunized mice. Production of IL-10 and IFN-gamma in these conditions was CD4-activation dependent. Concanavalin A (Con A)-stimulated interleukin-4 (IL-4) production was higher in saponin-immunized mice than in CFA-immunized mice. IL-10 produced by LN cells from saponin-immunized mice suppressed IFN-gamma production and Con A-induced proliferation. Taken together, these data are consistent with in vivo stimulation of both T-helper (Th)1 and Th2-type cells by immunization with saponin; in vitro a Th2-type cytokine response with high IL-10 production predominates, indicating preferential priming towards a Th2-type response. Immunization with CFA induced a Th1-type cytokine response. To our knowledge this is the first report in which an adjuvant is shown to prime for a dominant IL-10 production.

Chagas' disease: enhancement of systemic inflammatory reaction in cyclophosphamide treated mice

An explanation was sought for the fact that an enhancement of myocarditis occurs when Trypanosoma cruzi infected mice is treated with cyclophosphamide (CY). Several schedules were tested in mice and two polar models were achieved--one presenting parasite exacerbation without inflammatory reaction and the other presenting only cellular infiltrate in function of timing and different dosage of drug. In those receiving the drug after infection, an enhancement of the parasite load was detected and it was associated with an inflammatory reaction when mice were treated every other day with low doses of CY (3 mg/kg), but such inflammation was not present if a single dose of 200 mg/kg was used 5 days after infection. On the other hand, in schedules using 200 mg/kg of CY 2 days before infection an enhancement of myocarditis was observed on day 12 post infection, but this was not associated with parasite proliferation. Finally when employing a single intermediate dose of 40 mg/kg, a parasite load as well as a myocarditis enhancement was observed. A correlation between blood monocytes rebound and the intensity of myocarditis has been observed, and the varying time of drug injection suggested that this cellular infiltrate modulates the parasite load. If the immunosuppressive period of the drug occurred during parasite tissue invasion, parasite load amplification would occur without myocarditis. This was achieved using a single dose (200 mg/kg) of CY five days after infection, since monocytosis occurs 7-8 days after drug injection, allowing for parasite multiplication in tissues. The present data bring a strong suggestion that the modulation of myocarditis and parasite load are directly correlated with the leukocytes rebound occurring after the depression period promoted by CY treatment.

Modulation of parasitemia and antibody response to Trypanosoma cruzi by cyclophosphamide in Calomys callosus (Rodentia, Cricetidae)

Calomys callosus a wild rodent, previously described as harboring Trypanosoma cruzi, has a low susceptibility to infection by this protozoan. Experiments were designed to evaluate the contribution of the immune response to the resistance to T. cruzi infection exhibited by C. calossus. Animals were submitted to injections of high (200 mg/kg body weight) and low (20 mg/kg body weight) doses of cyclophosphamide on days -1 or -1 and +5, and inoculated with 4 x 10(3) T. cruzi on day O. Parasitemia, mortality and antibody response as measured by direct agglutination of trypomastigotes were observed. Two hundred mg doses of cyclophosphamide resulted in higher parasitemia and mortality as well as in suppression of the antibody response. A single dose of 20 mg enhanced antibody levels on the 20th day after infection, while an additional dose did not further increase antibody production. Parasitemia levels were not depressed, but rather increased in both these groups as compared to untreated controls. Passive transfer of hyperimmune C. callosus anti-T. cruzi serum to cyclophosphamide immunosuppressed animals resulted in lower parasitemia and mortality rates. These results indicate that the immune response plays an important role in the resistance of C. callossus to T. cruzi.

Enumeration of Trypanosoma cruzi-specific antibody-secreting cells by solid-phase immunoenzymatic technique

A specific and sensitive enzyme-linked immunoassay is applied for enumeration of cells secreting specific antibodies to Trypanosoma cruzi antigens. Spleen cells from immunized mice are incubated in antigen-coated plastic tissue culture plates. Individual antibody-producing cells secrete antibody which binds to the antigen at close vicinity of the cells. The areas of bound antibodies are demonstrated by an enzyme-linked antibody assay as dark round spots, which can be easily enumerated. This assay allows the enumeration of specific antibody-secreting cells to parasite antigens, overcoming the failures to develop conventional plaque-forming cells assays to complex antigens.

Specific suppression of delayed hypersensitivity expression to Trypanosoma cruzi in mice

The absence of cutaneous delayed type hypersensitivity (DTH) expression was investigated in Trypanosoma cruzi infected mice. Neither spleen cells nor peritoneal exudate cells from infected mice transferred DTH to normal recipients in local or systemic adoptive transfer experiments. Expression of DTH in T. cruzi immunized mice was suppressed specifically by Thy-1 negative spleen cells from acutely and subacutely infected animals. Suppression was observed only upon systemic transfer, but not when infected mice spleen cells were added to DTH effector cells and transferred to normal recipients. These results suggest that cutaneous DTH expression in acutely infected mice, might be blocked by mechanisms other than those described for suppression of lymphocyte proliferation and of DTH induction to T. cruzi.

Specific cutaneous hypersensitivity responses in mice infected or immunized with Trypanosoma cruzi

The appearance and development of cutaneous hypersensitivity to epimastigote antigen was followed during the early phase of Trypanosoma cruzi infection in mice. The effect of living BCG on the kinetics of skin reactivity was studied in animals infected with T. cruzi blood trypomastigotes or artificially immunized with disrupted epimastigotes. BCG stimulated the immediate response in infected animals while preferentially stimulating delayed responses in immunized animals. Infection with living blood trypomastigotes depressed already existing delayed-type responses. The development of delayed-type responses was also impaired in animals immunized in the course of the infection.

Evaluation of the immunosuppression in an experimental model of autoimmunity: suppressor activity of spleen cells from cyclophosphamide-treated rats

Rats immunized with chemically modified rat male accessory glands (MRAG) and injected 3 days later with cyclophosphamide (CY) were unable to develop humoral and cellular immune response to the autoantigen of MRAG. The present report demonstrates that the spleen mononuclear (SpM) cells transference from rats injected with CY 3 days after the antigen to normal male or female syngeneic animals before immunization with MRAG did not suppress the immune response to this antigen, whereas the transference of SpM cells from suppressed animals to animals previously immunized, depressed the delayed type hypersensitivity (DTH) response against MRAG (suppression of the expression) only in male rats. Similar results were obtained by transference of purified T cells. SpM cells did not suppress an established humoral immune response induced in male or female rats. The results suggest that non-adherent cells present in the spleen of male suppressed rats might be one of the responsible mechanisms for suppression of the efferent phase of the cellular autoimmune response to MRAG.