B and T cell activation in the absence of IRAK4. (A) Partial defect in BCR-induced B cell expansion in the absence of IRAK4. Splenic IRAK4+/+ and IRAK4-/- B cells from RAG1-/- mice reconstituted with IRAK4+/+ or IRAK4-/- BM cells were stimulated as in Figure 1A. Proliferation was measured by [3H]thymidine incorporation. Results are presented as the mean [3H]thymidine incorporation ± S.D. for 6 independent experiments after an 8 h pulse. The data were analyzed using the dependent (paired samples) t-test. (B) IκBα degradation after anti-IgM stimulation of IRAK4-/- B cells. Splenic IRAK4+/+ and IRAK4-/- B cells from reconstituted RAG1-/- mice were stimulated as in Figure 1B and IκBα degradation and phosphorylation (P-IκBα), ERK1/2 phosphorylation and actin levels were analyzed by Western blotting. (C) Normal TCR-induced proliferation of IRAK4-/- T cells. Upper panel: Purified IRAK4+/+ and IRAK4-/- T cells from reconstituted RAG1-/- mice were stimulated for the indicated times with anti-CD3 in the absence or presence of anti-CD28, or with TPA/Ca2+ ionophore A23187 (I). Lower panel: Purified T cells were mixed with irradiated WT splenocytes and stimulated as in the upper panel. For both sets of panels, proliferation was measured as in (A). Results are presented as the mean [3H]thymidine incorporation ± S.D. for 3 independent experiments after an 8 h pulse.