Intrathymic changes in murine CD3, CD5 and CD8 expression after in vivo administration of anti-CD4

Intrathymic development of murine cortical and medullary thymocyte subpopulations was examined after in vivo administration of anti-CD4 mAb. Four days after mice received 1 mg anti-CD4, expression of CD4 was reduced to about 25% the levels of controls. On cortical CD8+/PNAhigh thymocytes, CD5 and CD8 expression both decreased, but not in parallel, whereas CD3 expression increased almost 2-fold. Partial shifts in CD3 expression were seen 3 and 6 h after injection, but modulation of CD4 preceded the increase in CD3 expression. On medullary CD8-/PNAlow thymocytes, both CD3 and CD5 were down regulated. On nontargeted CD8+/PNAlow medullary thymocytes, expression of these molecules was decreased less than 20%, but the decrease in CD8 expression was primarily due to the appearance of a CD8low subpopulation. The results indicate that anti-CD4 mAb differentially affects the intrathymic development of T cell populations.