Antibodies against CD99L2 do not affect lymphocyte transmigration in vitro and lymphocyte extravasation in vivo. (A) Transendothelial migration of SJL.PLP7 T lymphocytes is not affected by anti-CD99L2 antibodies. SJL.PLP7 cells were allowed to transmigrate through a monolayer of bEnd.5 cells grown on transwell filters for 30 minutes in the presence of 100 ng/mL SDF-1 in the lower chamber. Endothelial cells were incubated for 30 minutes before the assay either without antibodies (w/o Ab) or with preimmune control IgG (co-IgG), affinity purified anti-CD99 IgG (anti-CD99), affinity purified anti-CD99L2 IgG (anti-CD99L2), or a monoclonal antibody against ICAM-1 (anti-ICAM-1). Antibodies (each 30 μg/mL) remained present during the assay. Each panel is representative of at least 3 experiments; each measurement was done in triplicate. ***P < .001 anti-CD99 versus co-IgG. (B) Migration of lymphocytes into inflamed skin is not affected by anti-CD99L2. Radiolabeled in vivo-activated T cells were injected intravenously into hapten-challenged mice together with (50 μg each) control IgG from preimmune serum (co-IgG), or monoclonal antibodies against P-selectin and E-selectin (anti–P-/E-selectin), affinity-purified antibodies against ESAM (anti-ESAM), or affinity-purified antibodies against CD99L2 (anti-CD99L2). The bar on the left represents radioactivity accumulating in the noninflamed ear. Statistical analysis was done by Student t test. Results are representative for 3 similar experiments; for each determination, 4 mice were analyzed. Numbers on the left refer to the percentage of injected cells that were found in the analyzed ear.