Cognate recognition of ECs enhances antigen-specific T-cell diapedesis in vivo. Cognate recognition of endothelial cells enhances antigen-specific T-cell diapedesis in vivo. Male C57BL/6 (H2^b; ▪), congenic male B10.BR (H2^k, ▦), or BALB/C and CBA/Ca (H2^d, H2^k; □) mice were treated with intrascrotal administration of IFN-γ (600 U in 400 μL saline). After 72 hours, fluorescently labeled HY-specific T cells (“Materials and methods”) were injected intravenously after surgical exteriorization of the cremaster muscle and T-cell interactions with venular walls were visualized and quantified by intravital microscopy for up to 40 minutes after injection of the cells (“Materials and methods”). Results are from 3 to 5 mice per group, and significant differences between the H2^b in comparison with the H2^k and H2^d or the H2-congenic H2^k strains of mice are shown by asterisk (^*P < .05). (A) T-cell firm adhesion. (B) Extravasation.