Nonspecific immunodepression and protective immunity in mice infected with Leishmania mexicana

Immuno-biochemical evaluations of phenol and thimerosal as antigen preservatives in Montenegro skin test

Montenegro skin test (MST) represents the main complementary diagnostic test for tegumentary leishmaniases (TL) in endemic regions. Most antigen formulations used for the MST contain thimerosal as preservative. The Food and Drug Administration (FDA), however, recommended reducing or eliminating thimerosal from vaccines and other biological reagents and the Agência Nacional de Vigilância Sanitária (ANVISA) in Brazil, prohibited the use of mercurial compounds in immunobiologicals. In the search for an alternative stabilizer, phenol and thimerosal were tested as antigen preservatives in MST. Formulations were tested when fresh and after a 12-month storage at 4 degrees C in TL confirmed mice and human patients, and were evaluated for protein constitution by SDS-PAGE, Western blot and anti-gp63 ELISA. In mice, a decrease in the diagnostic effectiveness in merthiolate formulation was observed after a 12-month storage. SDS-PAGE, Western blot and anti-gp63 ELISA analyses showed a degradation of antigen proteins in both formulations after 12-month storage and that phenol-preserved antigen was quantitatively and qualitatively better than the merthiolate-preserved one. In patients, the average of induration diameter was larger in fresh antigens (p<0.05). However, storage time did not jeopardize their diagnostic capacity. No non-specific reactions produced by phenol or merthiolate were observed neither in humans nor in mice. Phenol could be a good alternative to replace the merthiolate in MST, and despite the proteolytic activity, antigens remain viable for at least 12 months.

Vaccination of C57BL/10 mice against cutaneous Leishmaniasis using killed promastigotes of different strains and species of Leishmania

Antigenic extracts from five Leishmania stocks were used to vaccinate C57BL/10 mice. The Leishvacin(R) and PH8 monovalent vaccine yielded the highest IFN-gamma levels in the supernatants of spleen cell culture from vaccinated animals. Each single strain immunized group showed evidence of protective immunity six months after the challenge with promastigotes of Leishmania (Leishmania) amazonensis. No differences were detected between the vaccinated groups. It can be concluded that vaccines composed of single Leishmania stocks can provide protection to C57BL/10 mice against L. (L.) amazonensis infection.

Immune responses to T-dependent and T-independent antigens during visceral leishmaniasis in mice: evidence for altered T-cell regulation of immune responses to non-parasite antigens

Antibody responses to T-dependent and T-"independent" antigens were studied in disease-susceptible (BALB/c and C57BL/10) and disease-resistant (A/J) mice infected with Leishmania donovani chagasi. Disease-susceptible mice but not disease-resistant mice showed a transient decrease in PFC responses to TNP on a T-dependent carrier (BGG) during the period of 4-8 weeks after infection. Infected disease-susceptible animals also showed increased responses to TNP on a type II T-independent carrier (Ficoll), which persisted until at least 14 weeks after infection. The increased responses were associated with a significant increase in anti-TNP antibody of the IgG2b subclass. When T-enriched spleen cells from infected mice and B-enriched spleen cells from uninfected mice were transferred to irradiated recipients immunized with TNP-Ficoll, increased anti-TNP PFC were observed over numbers seen in irradiated recipients which received both B and T cells from uninfected mice. Increased responses to TNP-Ficoll were also induced by prior administration of soluble leishmania extract in CFA. Infected mice immunized with TNP-LPS, a T-independent type I antigen, also had increased anti-TNP antibody responses, but had normal anti-LPS antibody responses. The elevated antibody production which occurred in response to the T-"independent" antigens could not be attributed to the relatively low polyclonal response which occurred in both disease-resistant and disease-susceptible mice infected with L. donovani chagasi. The observations are consistent with leishmania induced, transient alterations in some T-cell functions including response to haptens on T-dependent carriers, and a lack of down regulation of T-"independent" responses. Subtle lesions in immunoregulation may be important correlates of successful protozoal infection and may be responsible for some of the immunologic manifestations of the disease.

Hypergammaglobulinaemia in Leishmania donovani infected hamsters: possible association with a polyclonal activator of B cells and with suppression of T cell function

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.

The effect of protein restriction on the development of protective immunity to Leishmania mexicana

Protein deprived C57BL/6 mice infected with 10(3) amastigotes of Leishmania mexicana showed early arrest of lesion progression during the first 5 weeks of infection with subsequent development of progressive non-healing lesions. In contrast, well nourished mice similarly infected developed gradual healing lesions. The early resistance of malnourished mice to 10(3) amastigotes was overcome by a larger dose. After a primary inoculation with 10(3) amastigotes protein deprived mice failed to express protective immunity to a challenge inoculum given at 5 weeks of infection. When challenge was delayed until 10 weeks, protein deprived mice developed lesions at the site of challenge which tended to regress but were unable to manifest the high level of protective immunity seen in normally nourished reinfected controls. A challenge infection given at 5 or 10 weeks prejudiced the control of primary lesions particularly in the group of protein deprived mice challenged at 10 weeks. Equivalent levels of specific delayed hypersensitivity responses were found in protein deprived and normally nourished uninfected mice immunized with killed parasites which imply that the impaired protective immunity observed in protein deprived mice is not due to a deleterious effect of protein deprivation on the ability of the host to develop cellular responses such as delayed type hypersensitivity to Leishmania antigens.

Immune responsiveness following intratracheal inoculation with Histoplasma capsulatum yeast cells

Splenic in vitro immune responses from C57B1/6 mice have been evaluated after intratracheal (i.t.) or intravenous (i.v.) inoculation with live Histoplasma capsulatum yeast cells. Significant (P less than 0.005) numbers of cells reactive to heat killed H. capsulatum (HK-Hc) were present 1 week after i.t. inoculation with 5 X 10(5) viable yeast cells. In contrast, blastogenic responses to HK-Hc were not detected until 3 weeks after i.v. H. capsulatum inoculation. Examination of non-specific immunity, i.e. mixed lymphocyte responses to alloantigens and antibody formation to sheep erythrocytes, revealed a significant (P less than 0.005) and transient depression of these responses 1 week following i.t. H. capsulatum inoculation. The non-specific decreases associated with early (1 week) i.t. infection were not mediated by suppressor cells but were related to the number of viable yeast administered.

Characterization of the cellular immune response in American cutaneous leishmaniasis

The in vitro and in vivo cellular immune reactivity of 49 patients with American cutaneous leishmaniasis (ACL) was evaluated using mitogens and parasite antigens. Patients were examined before treatment and were classified on the basis of clinical and histopathological criteria as suffering localized cutaneous leishmaniasis (LCL, 32 patients) or mucocutaneous leishmaniasis (MCL, 11 patients). A small group (6 patients) of treated diffuse cutaneous leishmaniasis (DCL) patients was also examined. The lymphocyte proliferative responses to PHA were significantly lower than those of controls (87 individuals, from either endemic or nonendemic zones) in LCL, and particularly MCL. Con A responses were, however, effectively normal in these patients. Both in vivo and in vitro cellular immune responses to leishmanial antigens were significantly greater in MCL and LCL patients than in the controls, the intensity of the reactions being by far the greatest in MCL. DCL patients demonstrated a complete absence of specific immune responsiveness both in vivo and in vitro. The significance of these results in the mechanisms leading to the resolution of the infection or production of pathologic lesions is discussed.

Blastogenic responses of lymphocytes from mice immunized by sublethal infection with yeast cells of Histoplasma capsulatum

Blastogenic responses of spleen cells to histoplasmin and ribosomal antigens and to the mitogens concanavalin A. phytohemagglutinin, and lipopolysaccharide were studied in normal and immunized mice (10(5) live yeast cells of Histoplasma capsulatum given by the subcutaneous route). Cells (10(6) per well) were cultured with and without antigens and mitogens in microtiter plates with RPMI 1640-5% heat-inactivated normal mouse serum for 72 h at 37 degrees C. Cells were harvested after a 16- to 18-h pulse with 1 microCi of [3H]thymidine (6.7 Ci/mol), and thymidine incorporation was measured by scintillation counting. The initial blastogenic response to concanavalin A (54 X 10(3) cpm) was suppressed (P less than 0.001) from 4 to 14 days post-immunization and returned to control levels on day 21. The response to phytohemagglutinin was suppressed up to 21 days. Lipopolysaccharide responses, however, were affected to a lesser degree. Blastogenic responses to histoplasmin and H. capsulatum ribosomes were similar on day 0 in normal and immune lymphocytes, but by day 4 cells from immunized mice were more responsive (P less than 0.01). The maximum response to H. capsulatum antigens was detected on day 42 and was 9- to 16-fold higher than in controls. These results demonstrate in vitro responses of primed lymphocytes on exposure to H. capsulatum antigens and suppressed responses to mitogens during early stages of the immune response.