Visceral leishmaniasis (VL) or kala-azar is known to be associated with a mixed Th1-Th2 response, and effective host defense requires the induction of IFN-γ and IL-12. We address the role of the differential decline of IL-10 and TGF-β in response to sodium antimony gluconate (SAG) and amphotericin B (AmB), the therapeutic success of SAG and AmB in Indian VL, and the significance of IL-10 and TGF-β in the development and progression of post-kazla-azar dermal leishmaniasis (PKDL). In the active disease, PBMC from VL patients showed suppressed Ag-specific lymphoproliferation, IFN-γ and IL-12 production, and elevation of IL-10 and TGF-β. Cure corresponded with an elevation in IFN-γ and IL-12 production and down-regulation of IL-10 and TGF-β. Both CD4+ and CD8+ T cells were involved in IFN-γ and IL-10 production. Interestingly, the retention and maintenance of residual IL-10 and TGF-β in some SAG-treated individuals and the elevation of IL-10 and TGF-β in PKDL, a sequel to kala-azar, probably reflects the role of these cytokines in reactivation of the disease in the form of PKDL. Contrastingly, AmB treatment of VL resulted in negligible TGF-β levels and absolute elimination of IL-10, reflecting the better therapeutic activity of AmB and its probable role in the recent decline in PKDL occurrences in India. Moreover, elucidation of immune responses in Indian PKDL patients revealed a spectral pattern of disease progression where disease severity could be correlated inversely with lymphoproliferation and directly with TGF-β, IL-10, and Ab production. In addition, the enhancement of CD4+CD25+ T cells in active VL, their decline at cure, and reactivation in PKDL suggest their probable immunosuppressive role in these disease forms.

IL-10-producing CD3+CD8+ lymphocytes are important protagonists in the immunopathogenesis of Indian PKDL.

Indian post-kala-azar dermal leishmaniasis (PKDL) is a low-frequency (5-10%) dermal sequela of visceral leishmaniasis (VL) caused by Leishmania donovani; importantly, affected individuals are speculated to be parasite reservoirs. Insight into its immunopathogenesis could translate into rational immunomodulatory therapeutic approaches against leishmaniases. In patients with PKDL (n=21), peripheral lymphocytes were analyzed for surface markers, intracellular cytokines, and lymphoproliferative responses using flow cytometry. In lesional tissue biopsies (n=12), expression of counter-regulatory cytokines (IFN-gamma and IL-10) and the T-regulatory transcription factor forkhead box protein 3 (Foxp3) was analyzed using reverse transcriptase-PCR, along with immunohistochemical detection (n=8) of CD3 and Foxp3 positivity. In patients with PKDL, circulating CD8(+)CD28(-) and antigen-induced IL-10(+)CD3(+) lymphocytes were increased and receded with treatment. CD8(+) lymphocytes showed impaired proliferative responses to L. donovani antigen (LDA) and phytohemagglutinin, which were reinstated after treatment. At presentation, the upregulated lesional IFN-gamma and IL-10 messenger RNA (mRNA), Foxp3 mRNA, and protein were curtailed after treatment. In Indian patients with PKDL, increased frequency of the CD8(+)CD28(-) phenotype, enhanced antigen-specific IL-10 production, and accompanying anergy of circulating lymphocytes suggest their regulatory nature. Furthermore, the concomitantly elevated lesional expression of Foxp3 suggests their possible recruitment into the lesional site, which would sustain disease pathology.

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In VL, monocyte functions were severely impaired facilitating parasite persistence; anti-leishmanial chemotherapy mediated parasite elimination through modulation of the macrophage microenvironment by restoring its redox status and antigen presenting capacity.