Increase of Thy-1 antigen on the thymocytes accompanied with their augmented adhesion capacity to thymic epithelial cells in the mice infected with Listeria monocytogenes.

It becomes increasingly clear that adhesion systems such as CD2/LFA-3 (lymphocyte function-associated antigen-3), LFA-1/ICAM-1 (intercellular adhesion molecule-1) and Thy-1/putative Thy-1 ligand participate in the association between murine thymocytes and thymic epithelial cells. In the present study, thymocytes showed an increase in surface Thy-1 levels in mice infected with Listeria monocytogenes, but no significant changes in the levels of CD2 or LFA-1. No alteration was found either in the ratio of CD3high/CD3low/CD3- or in that of CD4/CD8 subsets in these thymocytes compared with uninfected control thymocytes which excluded the possibility of enrichment of 'cortical thymocytes' with Thy-1high/CD3low/CD4+ CD8+ in the thymocyte population of infected mice. Moreover such Thy-1high thymocytes exhibited a highly augmented ability of adhesion to a thymic epithelial cell line due to the increase of surface Thy-1 antigens as an adhesion molecule. At such intervals after infection, the total number of thymocytes was found to be reduced. These results suggest that the expression level of surface Thy-1 on thymocytes is regulated in response to in vivo stimulation and may play a role in the intrathymic development of thymocytes by affecting the adhesion of thymocytes with thymic stromal cells. The implication of the enhanced ability of adhesion in the decrease in the number of thymocytes is discussed.