EphA1 and EphA4 are expressed in CD4⁺ T cells. (A) Expression of EphA4 and EphA1 mRNA by Northern blot analysis of peripheral blood CD4⁺ T cells (0 indicates freshly isolated) and after CD3/CD28 stimulation (1 indicates day 1; and 3, day 3). Control gene hybridization with an actin probe. (B) EphA1 cell surface expression on peripheral blood CD4⁺ T cells (Day 0), after CD3/CD28 stimulation (Day 1, Day 3), or on peripheral blood CD19⁺ B cells (CD19⁺). Anti-EphA1 (- - -), isotype specific control antibody (—). No binding is observed to CD19⁺ B cells. (C) Specificity of the anti-EphA1 antibody was shown by the loss of cell surface binding after preincubating the antibody with the extracellular part of recombinant EphA1 (EphA1-Fc). Peripheral blood CD4⁺ T cells were stained. (- - -) EphA1 expression, (—) EphA1 expression after preincubation of the anti-EphA1 antibody with EphA1-Fc before cell surface staining.