Reassessment of immune correlates in human visceral leishmaniasis as defined by cytokine release in whole blood

Depressed cell mediated immunity in human visceral leishmaniasis (VL), revealed as the inability of peripheral blood mononuclear cells (PBMCs) to respond to Leishmania antigen, remains a hallmark of and is thought to underlie the progressive nature of this disease. We have recently reported the ability of a whole blood, IFN-gamma release assay to detect sub-clinical infections amongst healthy individuals living in the kala-azar endemic zone in Bihar, India, and the surprising result that patients with active VL also secreted significant levels of antigen-specific IFN-gamma in this assay. We were interested to extend these findings to a larger cohort of subjects, and to employ the whole blood assay to detect additional cytokines that might better correlate with the disease status of infected individuals. We evaluated IFN-gamma, TNF-alpha and IL-10 release in 35 patients with active VL, 54 cured VL, 27 patients with other diseases, 52 Non-Endemic Healthy Controls (NEHC), and 147 Endemic Healthy Controls (EHC). The cellular response of the EHCs was correlated with their serological antibody titers against L. donovani and Phlebotomus argentipes saliva. The whole blood cells from the majority of both active (80%) and cured (85%) VL patients, as well as 24% of EHCs with presumed sub-clinical infections, produced significantly elevated levels of IFN-gamma. The findings do not support a severe Th1 response defect in kala-azar. Importantly, only the active VL patients also produced IL-10, which in conjunction with IFN-gamma better reflects the immune responses that distinguish active cases from cured or sub-clinically infected, immune individuals.