Sialyl lewisx antigen-expressing human CD4+ T and CD8+ T cells as initial immune responders in memory phenotype subsets

Cytokine production by memory T cells in secondary immune responses has a critical role in host defenses. Previously, we had demonstrated that a unique antigen composed of sialyl lewisx (sLex) was expressed on CD45RO+ memory‐phenotype subsets of human T cells. Here, we found that the sLex antigen was up‐regulated on CD45RA+ naïve human CD4+ T and CD8+ T cells by TCR stimulation. In addition, sLex antigen‐expressing CD4+ T and CD8+ T cells in human PBMCs were activated immediately by cytokine stimulations composed of IL‐2 plus IL‐12 or IL‐15 in an antigen‐independent manner. Moreover, the sLex‐positive human CD8+ T cells significantly enhanced reverse antibody‐dependent cellular cytotoxicity compared with a sLex‐negative population. These findings clearly indicate that sLex antigen‐expressing memory phenotype CD4+ T and CD8+ T cells contribute to early‐stage immunity by providing a source of IFN‐γ and cytotoxicity, suggesting that they would be a key immunomodulator in host defenses.