Ephrin-A1 binds to CD4⁺ lymphocytes. (A) Binding of control-Fc (—) and ephrin-A1-Fc (- - -) to peripheral blood isolated CD4⁺ T cells (CD4⁺) or CD19⁺ B cells (CD19⁺). No binding is observed to CD19⁺ B cells. (B) Costaining of peripheral blood CD4⁺ T cells with ephrin-A1-Fc and either CD45RA, CD45RO, or CD62L. The ephrin-A1 nonbinding cells are CD45RO⁺ and CD62L^-. (C) Costaining of control-Fc or ephrin-A1-Fc with anti-CD4 on a total tonsil cell preparation. (D) Binding of control-Fc (—) or ephrin-A1-Fc (- - -) to peripheral blood CD4⁺ T cells stimulated with anti-CD3/CD28 (day 1, day 3). Day 0 indicates freshly isolated cells.