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
dimCD56
+NKT and CD8
brightCD56
+NKT cells. We further analyzed the functional nature of CD8
dim and CD8
bright positive CD56
+NKT cells. In comparison to CD8
brightCD56
+NKT cells, a significantly higher percentage of CD8
dimCD56
+NKT cells expressed KIR during VL. The percentage of CD8
dimCD56
+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
brightCD56
+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
dimCD56
+NKT and CD8
brightCD56
+NKT cells during visceral leishmaniasis. The percentage of granzyme B expressing CD8
dimCD56
+NKT cells was 2.83 fold higher in VL compared to healthy subjects. But, there was no significant difference in granzyme B expressing CD8
brightCD56
+NKT cells in samples from healthy and VL subjects. However, within VL subject, the percentage of granzyme B expressing CD8
dimCD56
+NKT cells was 5.7 fold higher in comparison to CD8
brightCD56
+NKT cells. This study concludes that CD8
dimCD56
+NKT cells are more cytotoxic than CD8
brightCD56
+NKT cells during VL.
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