IMMUNODOMINANCE ANALYSIS OF CTL RESPONSES TO INFLUENZA PR8 VIRUS REVEALS 2 NEW DOMINANT AND SUBDOMINANT K-B-RESTRICTED EPITOPES

In the present study, a systematic analysis of the influenza (Flu) PR8 determinants recognized by H-2(b) mice was undertaken. A single Db-re stricted immunodominant epitope (NP366) was previously known in this s ystem, Twenty-three different Flu PR8-derived peptides that bound eith er K-b or D-b molecules in vitro were identified. Sixteen were immunog enic following peptide immunization of C578L/6 mice, yet CTL induced b y peptide immunization recognized PR8-infected target cells only in th e case of the NP366 and NS2(114) epitopes. Similarly, CTL responses fo llowing whole-PR8 virus immunization were detected only for the same t wo determinants. CTL recognizing these dominant epitopes had high avid ity for peptide-pulsed target cells, with 5 to 200 pM of peptide requi red for 30% specific lysis. In contrast, most (80%) of the remaining e pitopes were recognized with lower avidity (30% effective concentratio n in the range of 0.4-50 nM). Repeated in vitro stimulation of primary CTL cultures revealed one additional K-b-restricted epitope (Mi(128)) . This peptide bound K-b with high affinity (4.6 nM) and induced CTL t hat effectively recognized PR9-infected cells. These results suggest t hat 1) this epitope is produced by natural processing in relatively hi gh amounts and 2) low precursor frequency might be related to the subd ominant status of the M(128) epitope. Taken together, these results il lustrate the crucial contributions of MHC-binding capacity, and T cell repertoire availability, to the shaping of the repertoire of CTL spec ificities for Flu Ag virus.