A nucleoside analogue, 7-thia-8-oxoguanosine stimulates proliferation of thymocytes in vitro.

7-thia-8-oxoguanosine (immunosine) is a nucleoside analogue with immunoenhancing activity. In this work, its effects on proliferation of thymocytes in vitro were studied. It was found that immunosine stimulated proliferation of thymocytes both of mice and rats. The stimulatory effect depended on antigen presenting cells (APC), since thymocytes depleted of accessory cells did not proliferate to immunosine. In addition, pretreatment of APC with immunosine for 24 h significantly increased proliferation of thymocytes. Immunosine stimulated interleukin 2 (IL-2) production and the expression of activation markers (CD25 and CD71). The upregulation of CD25 (alpha subunit of IL-2R) was detected both on thymocytes and thymic dendritic cells. Proliferation of thymocytes in the presence of immunosine was predominantly mediated by IL-2 since blocking IL-2Ralpha by specific monoclonal antibodies inhibited cell proliferation by 65-85%.