Control of Visceral leishmaniasis (VL), a parasitic disease caused by L. donovani, requires robust CD4 +T cells response to control the parasite replication by IFN-γ production and activation of macrophages. Our recent study on transcriptional signature of CD4 +T cell isolated from peripheral blood of active VL patients showed enhanced expression of genes related to cytotoxicity. In present study, we investigated expression of these cytotoxic molecules including granzyme B (GZMB), Granulysin, Perforin and NKG7 on different CD4 +T cell subsets to establish the role of GZMB in regulating CD4 +T cells functional capacity. PBMCs cells were isolated from active and post treated VL patients and endemic controls, and flow cytometry was performed. LAMP assay (CD107b expression) was performed to study the degranulation capacity of CD4 +T cells. Whole blood assay followed by ELISA was performed to measure antigen specific cytokine / GZMB production by CD4 +T cells. We found that activated and degranulating CD4 +T cells (CD38 +CD107 +) had higher expression of GZMB, Granulysin, perforin and NKG-7. Similarly, GZMB level in plasma and antigen stimulated whole blood culture supernatant were significantly elevated in active VL patient compared to post treatment and EC. There was no change is IFN-γ secretion when whole blood culture was stimulated with soluble leishmania antigen in presence of Con-A but a significant decline in IL-6 production was observed. In summary, VL CD4 +T cells show a cytolytic phenotype and further investigations are required to understand their differentiation and function, particularly for promoting anti-parasitic immunity for host protection and effective intervention or therapy.

Extramural Program of the National Institute of Allergy and Infectious Diseases, National Institutes of Health (TMRC grant number U19AI074321)