Abstract
Human T cells expressing CD56 are capable of tumour cell lysis following activation with interleukin-2 but their role in viral immunity has been less well studied. Proportions of CD56
+
T cells were found to be highly significantly increased in cytomegalovirus-seropositive (CMV
+
) compared with seronegative (CMV
−
) healthy subjects (9·1 ± 1·5% versus 3·7 ± 1·0%;
P
< 0·0001). Proportions of CD56
+
T cells expressing CD28, CD62L, CD127, CD161 and CCR7 were significantly lower in CMV
+
than CMV
−
subjects but those expressing CD4, CD8, CD45RO, CD57, CD58, CD94 and NKG2C were significantly increased (
P
< 0·05), some having the phenotype of T effector memory cells. Levels of pro-inflammatory cytokines and CD107a were significantly higher in CD56
+
T cells from CMV
+
than CMV
−
subjects following stimulation with CMV antigens. This also resulted in higher levels of proliferation in CD56
+
T cells from CMV
+
than CMV
−
subjects. Using Class I HLA pentamers, it was found that CD56
+
T cells from CMV
+
subjects contained similar proportions of antigen-specific CD8
+
T cells to CD56
−
T cells in donors of several different HLA types. These differences may reflect the expansion and enhanced functional activity of CMV-specific CD56
+
memory T cells. In view of the link between CD56 expression and T-cell cytotoxic function, this strongly implicates CD56
+
T cells as being an important component of the cytotoxic T-cell response to CMV in healthy carriers.