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

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 CD8dimCD56+NKT and CD8brightCD56+NKT cells. We further analyzed the functional nature of CD8dim and CD8bright positive CD56+NKT cells. In comparison to CD8brightCD56+NKT cells, a significantly higher percentage of CD8dimCD56+NKT cells expressed KIR during VL. The percentage of CD8dimCD56+NKT cells expressing KIR was found 4 fold higher in VL as compared to healthy subjects. But, the difference was insignificant in case of CD8brightCD56+NKT cells. CD8+CD56+NKT cells release granzyme B to kill the infected cells. A categorical difference was also observed in the function of CD8dimCD56+NKT and CD8brightCD56+NKT cells during visceral leishmaniasis. The percentage of granzyme B expressing CD8dimCD56+NKT cells was 2.83 fold higher in VL compared to healthy subjects. But, there was no significant difference in granzyme B expressing CD8brightCD56+NKT cells in samples from healthy and VL subjects. However, within VL subject, the percentage of granzyme B expressing CD8dimCD56+NKT cells was 5.7 fold higher in comparison to CD8brightCD56+NKT cells. This study concludes that CD8dimCD56+NKT cells are more cytotoxic than CD8brightCD56+NKT cells during VL.