Fig. 6. Effects of T. gondii infection on the phosphorylation of IB. MEFs were infected at increasing m.o.i. for 20 hours. Treatment of uninfected cells with TNF (20 ng ml^–1, 20 minutes) was used as a positive control. Immunoblots were performed with mouse monoclonal anti-P-IB, polyclonal rabbit anti-IB, and polyclonal rabbit anti-actin as described in the Materials and Methods section. (A) Elevated levels of P-IB were observed in infected MEFs but, unlike the TNF control, levels of IB were not decreased. (B) Treatment with 50 µM MG132 proteosome inhibitor for 2 hours prior to TNF stimulation caused an accumulation of P-IB and prevented degradation of the protein. In contrast to this, no apparent increase in P-IB accumulation was observed in T.-gondii-infected cells treated with 50 µM MG132 for 2 hours prior to immunoblot analysis.