The recombinant product (rK39) of the 39 amino acid repeats encoded by a kinesin-like gene of visceral Leishmania spp. was further evaluated by enzyme-linked immunosorbent assay (ELISA) for its diagnostic potential in Indian kala-azar (VL) and post kala-azar dermal leishmaniasis (PKDL). Anti-rK39 antibodies were highly positive in 20 symptomatic cases, including 6 resistant to single or double chemotherapy, but became negligible or absent in 9 recently cured patients. Endpoint titration of samples from the 20 active cases showed that the anti-rK39 IgG titers fell within a wide range of 10(-2) to > 10(-6), and that their mean was > 1 order of magnitude higher than in VL reported previously. The anti-rK39 IgG titers were correlated with parasite burden found in the patients and remained undiminished in those refractory to chemotherapy. These results indicate that: (1) the K39 epitope is conserved in Indian strains of Leishmania donovani, (2) the extremely high levels of K39 antibodies in both VL and PKDL suggest the application of rK39 for sensitive and specific serodiagnosis, and (3) rK39 ELISA is also valuable for prognostic evaluation of both diseases.

The ability of interleukin-7 (IL-7) to stimulate murine thymocyte proliferation was investigated. IL-7, either alone or in concert with lectin, induced proliferation of adult thymocytes as well as day 13 fetal and adult CD4-/CD8-thymocytes. The IL-7-induced proliferative response of unfractionated thymocytes could not be inhibited by antibodies to IL-2, or IL-4, IL-6, or the IL-2 receptor. In addition, IL-2, IL-4, and IL-6 were not produced by thymocytes activated with IL- 7, as judged by the absence of biologically active cytokine in IL-7- stimulated culture supernatants. IL-7 could act in concert with IL-2 and IL-4 or with IL-4 to enhance the proliferative response of thymocyte cultures. Thus, IL-7 may cause proliferation of thymocytes directly, not indirectly, through production of IL-2, IL-4, or IL-6. IL- 7 may then play a significant role in differentiation of T lymphocytes.

IL-12 is a pluripotent cytokine that interacts with NK and T cells to play a central role in the initiation and maintenance of Th1 responses and IFN-gamma production. Because of the interactive relationship between IL-12 and IFN-gamma response to infectious organisms, a study was undertaken to examine the role of IL-12 in the immune regulation of human visceral leishmaniasis (VL). Human (Hu) VL is associated with immune dysfunction and the appearance of IL-10 mRNA, not present in healed individuals. We found that PBMC from treated VL patients produced both IL-12 p40 and IFN-gamma in response to in vitro stimulation with Leishmania donovani. The production of both IL-12 p40 and IFN-gamma were interdependent and were abrogated by the addition of exogenous Hu rIL-10. In contrast, PBMC from active VL patients did not produce IL-12 p40 or IFN-gamma in response to L. donovani lysate. Neutralizing anti-IL-10 mAb led to the enhancement of IFN-gamma production by active VL PBMC cultured with L. donovani lysate, and this enhanced IFN-gamma production was blocked by anti-IL-12 mAb. The addition of exogenous Hu rIL-12 to PBMC from active VL patients resulted in the augmentation of IFN-gamma in response to L. donovani lysate. Therefore, treatment of active VL patient PBMC with anti-IL-10 or IL-12 shifted the response toward a Th1-type response with the production of IFN-gamma. These results indicate that IL-12 may play an important role in the regulation of the cellular immune responses in Hu VL.

Fresh normal human serum was observed to have a lethal effect on Leishmania mexicana amazonensis promastigotes obtained from laboratory-bred Lutzomyia longipalpis or on promastigotes grown in liquid culture medium, inoculated with the same isolates. Heat inactivation abolished the Leishmania lytic activity from the sera. Resistance of culture promastigotes to lysis by normal human serum was investigated in three isolates of L. m. amazonensis. Development of resistance (up to 7%) was found in only one isolate, obtained from the bone marrow in a human case of visceral leishmaniasis.

The regulation of murine T cell proliferation by IL-7 was investigated. Highly purified resting splenic T cells were induced to proliferate in a short term assay by IL-7 in the presence of the comitogen, Con A. The proliferation of these resting T cells showed both IL-2-dependent and -independent components as determined by the susceptibility of the response to the blocking effects of anti-IL-2 mAb. Furthermore, IL-7 was found to augment the Con A-induced production of IL-2 and expression of IL-2R by resting splenic T cells. In contrast, Con A blasts and long term, Ag-dependent cloned T cells proliferated in response to IL-7 independently of any involvement of IL-2. Finally, differences were observed between IL-7 and IL-6 with regard to the regulation of T cell growth and activation. As with IL-7, IL-6 stimulated resting splenic T cells to proliferate in the presence of comitogen. However, in contrast to IL-7, IL-6 failed to stimulate the proliferation of Con A blasts or T cell clones and did not augment the Con A-induced expression of IL-2R on resting T cells.