Fig. 10.

Secondary crosslinking of anti-mCD28 mAb overcomes the requirement for Tyr-188 in the costimulation of IL-2 by mCD28. Jurkat cells expressing WT, the all-phenylalanine mutant (All F), the Tyr-188 to phenylalanine mutant (Phe-188), or TL versions of mCD28 were stimulated with the combination of 1 μg/ml phorbol 12-myristate 13-acetate and 0.5 μM ionomycin. mAbs to either the endogenous hCD28 or to mCD28 were added as indicated either alone (–) or with a crosslinking goat anti-mouse antibody (XL). The levels of IL-2 in the supernatants were quantitated by ELISA. Shown are the results of experiments with two independently derived clones for each mCD28 mutant.