Differential<i>in vitro</i>CD4⁺/CD8⁺T-cell response to live vs. killed<i>Leishmania major</i>

Abstract

Clinical trials of killed Leishmania vaccines showed a limited efficacy compared with leishmanization (LZ). The reason for this difference in protection against cutaneous leishmaniasis (CL) is not known and in vivo studies on T-cell function may provide valuable information. Nevertheless, there are limited studies on the nature of the stimulatory effects of live vs. killed parasites on human T cells in vitro. A total of nine Leishmanin Skin Test+ volunteers with a history of self-healing CL (HCL) and seven healthy volunteers were included in this study. 5,6-carboxyfluroescein diacetate succinimidyl ester-labelled CD4(+)/CD8(+) lymphocytes were cultured with killed Leishmania Lysate (Killed LL) or live Leishmania major (Live LM) and analysed for proliferation using flow cytometry. Culture supernatants were used for cytokine titration. In HCL volunteers, upon stimulation with killed LL, the number of proliferated CD4(+)/CD8(+) cells was significantly more than that of unstimulated (P < 0.001) or live LM stimulated (P < 0.05) cells, or cells from controls (CD4(+)/CD8(+): P < 0.05/P < 0.001). Stimulation of CD4(+) cells with Live LM (P < 0.001) or Killed LL (P < 0.05) induced a significantly higher IFN-gamma production compared with that of controls, but Live LM induced significantly (P < 0.05) more IFN-gamma than Killed LL. A significantly (P < 0.05) higher IFN-gamma production was observed when CD8(+) cells were stimulated with Live LM. Cells from HCL volunteers showed significantly more IL-10 production to Live LM stimulation compared with that of controls (CD4(+): P < 0.05 /CD8(+): P < 0.001) or cells stimulated with Killed LL (CD4(+)/CD8(+): P < 0.001/P < 0.0005). Whereas Killed LL induced more proliferation response in purified T cells, Live LM induced cytokine production without significant induction of proliferation. The results from healed CL volunteers in this study could be implicated in further studies on T-cell response in vaccinated individuals.