Figure 2.

Coexpression of ICAM-1 promotes the appearance of the hyperphosphorylated p23 form of ζ. D011 CD4⁺ cells were stimulated for 5 min with the indicated concentration of ova peptide presented by Dros APC-expressing class II alone (IA^d), class II plus ICAM-1 (+ ICAM-1), or class II plus ICAM-1 plus B7.2 (+ ICAM-1 + B7.2). Cell lysates were immunoprecipitated with anti-CD3ɛ and the precipitated proteins were resolved on SDS/PAGE. After transfer, phosphorylated ζ was detected by blotting with antiphosphotyrosine (4G10) Ab. The p23ζ bands in the above blot were quantitated by densitometry and the relative volume was plotted. (B) A second experiment including Dros APC expressing B7.2.