CD4+ and CD8+ lymphocyte responses and cytokine profiles in visceral leishmaniasis patients following effective treatment in distinct transmission settings in Bihar, India

Visceral leishmaniasis (VL), caused by Leishmania donovani , is characterized by a complex immune response, with a dominant Th1 profile crucial for parasite elimination. This study aimed to assess the persistence of immune memory and cytokine responses in individuals with a history of VL, focusing on the activation and proliferative capacity of CCR7/CD45RA defined CD4 + and CD8 + lymphocyte populations corresponding to central memory-like and effector memory-like phenotypes. We examined three distinct groups from areas with different transmission histories: areas with no transmission (NT), areas with continuous transmission (CT), and areas experiencing an outbreak (OB). Using soluble Leishmania antigen (SLA)-stimulated whole blood assays and flow cytometry, we measured Th1, Th2, and Th17 cytokine levels, activation marker CD69 and proliferation marker Ki67 in CD4 + and CD8 + lymphocytes. SLA stimulation elicited significant increases in IFN-γ, IL-10 and IL-2 relative to unstimulated controls within the NT and OB groups and was not significant in CT group. In contrast, comparison of antigen specific responses among transmission settings demonstrated significantly lower ΔIL-10 response in the CT group, whereas ΔIFN-γ and ΔIL-2 responses were not significantly different. CD4 + CD45RA⁻CCR7 + , CD4 + CD45RA⁻CCR7⁻ CD8 + CD45RA⁻CCR7 + and CD8 + CD45RA⁻CCR7⁻ memory-phenotype lymphocyte subsets showed the higher absolute frequencies of activated cells in CT people, measured by expression of CD69, but not of proliferative responses. By contrast, the proliferation of CD4 + CD45RA⁻CCR7 + cells were increased in the OB group, underscoring variations in the functional nature of immunological memory between transmission circumstances. These findings indicate that while Th1 cytokine responses are preserved, the proliferative capacity of memory-phenotype lymphocytes varies by transmission setting, reflecting differences in antigen exposure and with implications for long-term protection and immune surveillance in VL elimination settings.