Figure 6.

Reconstitution of CD28 signaling in T cells from CD28-deficient mice requires proline residues at positions 187 and 190. Lymph node T cells from CD28-deficient animals were infected with retroviruses encoding either wild-type mCD28 or mCD28 lacking the 16 COOH-terminal residues (Δ16) or with the P187,190A mutated construct. 3 d after infection, T cells were stimulated with anti-CD3 antibodies, PMA, or anti-CD3 and PMA in combination with antibodies to mCD28. T cell proliferation was measured by [³H]thymidine incorporation. Retroviral transduction efficiency was measured by analyzing mCD28 surface expression using flow cytometry. Values are the means of quadruplicate samples. The data is representative of three independent experiments.