CD8dim but not CD8bright cells positive to CD56 dominantly express KIR and are cytotoxic during visceral leishmaniasis

Abstract This study reports a structural and functional heterogeneity of CD8 + CD56 + NKT cells, which usually decrease quantitatively during visceral leishmaniasis. Based on fluorescence intensity of CD8 receptors on CD56 + NKT cells, two populations of CD8 + CD56 + NKT cells have been identified. These cells were recognized as CD8 dim CD56 + NKT and CD8 bright CD56 + NKT cells. We further analyzed the functional nature of CD8 dim and CD8 bright positive CD56 + NKT cells. In comparison to CD8 bright CD56 + NKT cells, a significantly higher percentage of CD8 dim CD56 + NKT cells expressed KIR during VL. The percentage of CD8 dim CD56 + NKT cells expressing KIR was found 4 fold higher in VL as compared to healthy subjects. But, the difference was insignificant in case of CD8 bright CD56 + NKT cells. CD8 + CD56 + NKT cells release granzyme B to kill the infected cells. A categorical difference was also observed in the function of CD8 dim CD56 + NKT and CD8 bright CD56 + NKT cells during visceral leishmaniasis. The percentage of granzyme B expressing CD8 dim CD56 + NKT cells was 2.83 fold higher in VL compared to healthy subjects. But, there was no significant difference in granzyme B expressing CD8 bright CD56 + NKT cells in samples from healthy and VL subjects. However, within VL subject, the percentage of granzyme B expressing CD8 dim CD56 + NKT cells was 5.7 fold higher in comparison to CD8 bright CD56 + NKT cells. This study concludes that CD8 dim CD56 + NKT cells are more cytotoxic than CD8 bright CD56 + NKT cells during VL.