Fig. 4. Role of PA28α/β in antigen processing and immune responses against viral infection. (A) Presentation of the OVA257–264 epitope. LPS blasts from wild-type (open symbols) and PA28α–/–/β–/– (filled symbols) mice were osmotically loaded with the indicated doses of OVA proteins and labeled with 51Cr. The labeled cells were used as target cells for the lysis by OVA257–264-specific CTLs. (B) Mortality rates and relative body weight loss after infection with the influenza A virus strain PR8. Mice (n = 8 per group) were infected intranasally with the indicated doses of Flu PR8. Mortality rates in wild-type (dashed line) and PA28α–/–/β–/– (solid line) mice are shown on the left. Relative body weight loss in wild-type (open circles) and PA28α–/–/β–/– (filled circles) mice is shown on the right. Data represent the mean percentage body weight relative to the weight before infection. (C) CTL induction after Flu PR8 infection. Two weeks after infection with Flu PR8 (circles), splenocytes from wild-type (open symbols) and PA28α–/–/β–/– (filled symbols) mice were isolated, stimulated with synthetic peptide NS2114–121 or NP366–374 for 6 days, and used as effector cells. 51Cr-labeled EL-4 cells pulsed with NS2114–121 or NP366–374 were used as target cells. Splenocytes from non-infected mice (triangles) were used as a control. (D) Presentation of the TRP2181–188 epitope. LPS blasts from wild-type (open symbols) and PA28α–/–/β–/– (filled symbols) mice were osmotically loaded with the TRP2181–193 peptide (circles) or the TRP2181–188 peptide (triangles) and labeled with 51Cr. The labeled cells were used as target cells for the lysis by TRP2181–188-specific CTLs.