Inhibition of CD28 does not modify proliferative responses to KLH immunization.

Rats were immunized subcutaneously with 50 μg KLH in CFA. Recipients received intraperitoneally 1 mg control IgG or modulating anti–rat CD28 JJ319 or 0.5 mg CTLA4 immunoglobulin, as indicated, at days 0, 2, 4, and 6. Draining lymph node cells were collected after 2 weeks and were restimulated in vitro with 2.5 μg/mL KLH. Proliferation was measured after 3 days. (A) Mean proliferation of nonrestimulated cells was 5000 cpm. (B) In cultures from immunized but control-treated animals, control IgG, anti-CD28 Fab (10 μg/mL), or CTLA4 immunoglobulin (10 μg/mL) was added, and proliferation was measured after 3 days. *indicates significative at P < .05.