Reduced secondary responses in p85β-deficient mice. (A) p85β^−/− and p85β^+/− mice received an intraperitoneal injection of heat-inactivated C albicans to induce a primary response; 21 days later, some mice received an identical injection to induce the secondary response. Splenocytes or lymph nodes (LNs) were isolated and the cells analyzed by flow cytometry using appropriate antibodies. The figure shows CD4⁺ cell numbers at different times after injection (mean ± SD; n = 3). P values were calculated at day 5. (B) The NP_366-374 influenza peptide was injected into p85β^−/− and p85β^+/− F5TCRTg mice for a primary response; injection was repeated after 11 days for the secondary response. The figure shows CD8⁺/Vβ11⁺ spleen cell numbers at different times after injection (mean ± SD, n = 3). indicates peptide injection. (C) For primary in vitro proliferation assays, peripheral T cells from p85β^−/− and p85β^+/− F5TCRTg mice were activated with peptide-pulsed APCs at different peptide doses, alone or in the presence of IL-2 (10 U/mL). For secondary immune response, mice received a peptide injection and were killed after 10 days, when T cells were purified from spleen and lymph nodes. T cells were then activated in vitro. [³H]thymidine incorporation was measured at 48 hours (mean ± SD, n = 3). indicates the compared data for P value calculation (2 ng/mL peptide). (D) p85β^−/− and p85β^+/− F5TCRTg mice received NP_366-374 peptide at day 0 () to induce a primary IR; injection was repeated at day 11 for the secondary IR. Mice were killed at different times after peptide injection. T-cell activation/memory markers were analyzed in the CD8⁺/Vβ11⁺ population by flow cytometry. P values were calculated at 6 hours after secondary IR *P < .05).