Dynamics of immunosuppression in hamsters with experimental visceral leishmaniasis

Immunosuppression has been reported to occur during active visceral leishmaniasis and some factors such as the cytokine profile may be involved in this process. In the mouse model of cutaneous leishmaniasis using Leishmania (Leishmania) major, the Th1 response is related to protection while the Th2 response is related to disease progression. However, in hamsters, which are considered to be an excellent model for the study of visceral leishmaniasis, this dichotomy is not observed. Using outbred 45- to 60-day-old (140 to 150 g) male hamsters infected intraperitoneally with 2 x 10(7) L. (L.) chagasi amastigotes, we evaluated the immune response of spleen cells and the production of cytokines. We used 3 to 7 hamsters per group evaluated. We detected a preserved response to concanavalin A measured by index of proliferation during all periods of infection studied, while a proliferative response to Leishmania antigen was detected only at 48 and 72 h post-infection. Messenger RNA from cytokines type 1 (IL-2, TNF-α, IFN-γ) and type 2 (IL-4, IL-10 and TGF-β) detected by reverse transcriptase polymerase chain reaction and produced by spleen cells showed no qualitative difference between control non-infected hamsters and infected hamsters during any period of infection evaluated. Cytokines were measured by the DNA band intensity on agarose gel using the Image Lab 1D L340 software with no differences observed. In conclusion, the present results showed an antigen-dependent immunosuppression in hamsters with active visceral leishmaniasis that was not related to the cytokine profile.

Immunity and immunosuppression in experimental visceral leishmaniasis

Leishmaniasis is a disease caused by protozoa of the genus Leishmania, and visceral leishmaniasis is a form in which the inner organs are affected. Since knowledge about immunity in experimental visceral leishmaniasis is poor, we present here a review on immunity and immunosuppression in experimental visceral leishmaniasis in mouse and hamster models. We show the complexity of the mechanisms involved and differences when compared with the cutaneous form of leishmaniasis. Resistance in visceral leishmaniasis involves both CD4+ and CD8+ T cells, and interleukin (IL)-2, interferon (IFN)-gamma, and IL-12, the latter in a mechanism independent of IFN-gamma and linked to transforming growth factor (TGF)-á production. Susceptibility involves IL-10 but not IL-4, and B cells. In immune animals, upon re-infection, the elements involved in resistance are different, i.e., CD8+ T cells and IL-2. Since one of the immunopathological consequences of active visceral leishmaniasis in humans is suppression of T-cell responses, many studies have been conducted using experimental models. Immunosuppression is mainly Leishmania antigen specific, and T cells, Th2 cells and adherent antigen-presenting cells have been shown to be involved. Interactions of the co-stimulatory molecule family B7-CTLA-4 leading to increased level of TGF-á as well as apoptosis of CD4+ T cells and inhibition of macrophage apoptosis by Leishmania infection are other components participating in immunosuppression. A better understanding of this complex immune response and the mechanisms of immunosuppression in experimental visceral leishmaniasis will contribute to the study of human disease and to vaccine development.

Monoclonal antibodies against low density lipoprotein with various degrees of oxidative modifications

Oxidative processes leading to the generation of oxidized low density lipoprotein (oxLDL) particles have been suggested to be an important factor in the pathogenesis of atherosclerosis. After initiation of the oxidative process, LDL undergoes a progressive protein and lipid fragmentation. To understand this process and the role of oxLDL in various diseases of inflammatory origin, we have generated mouse monoclonal antibodies against copper-oxidized human LDL. Mice were immunized intrasplenically and after one intravenous boost the spleen cells were fused with the Sp2/0 hybridoma fusion partner. The hybridoma clones obtained after selection and cloning were analyzed for reactivity against oxLDL with various degrees of copper-mediated oxidative modifications. Three hybridoma clones were purified and further characterized. The following observations were made: 1) the intrasplenic route of immunization, avoiding the use of mycobacterial adjuvants, yielded a high frequency of positive clones; 2) the individual hybridomas reacted against LDL with various degrees of oxidative modifications; 3) the monoclonal antibodies could be used in ELISA and to detect oxLDL in immunohistochemical tissue staining, and 4) the monoclonal antibodies also detected oxLDL from hamsters and rabbits. We conclude that these monoclonal antibodies could be useful to further investigate the role of oxLDL in inflammation and in the immune response.