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Costimulatory Pathways CD40-CD40 Ligand and B7-CD28-CTLA-4 Minor Epitopes of Lysozyme Is Not Affected by Cells Responding to Chemically Dominant or Cutting Edge: The Relative Distribution of T

We examined the frequencies and speciﬁcities of the CD4 (cid:1) T cell responses to the protein hen egg white lysozyme in mice deﬁcient in the CD40-CD40 ligand or B7-CD28 costimulatory pathways. The frequency of T cells was decreased by between 3- and 4-fold in CD40 (cid:2) / (cid:2) mice, and 12-fold in B7-1/B7-2 (cid:2) / (cid:2) mice, but surprisingly, the relative distribution of T cells responding to peptides that were presented at levels that differed by > 250-fold was similar. We also examined the CD4 response after blocking the regulatory molecule CTLA-4 during immunization. We observed no difference in either the frequency or speciﬁcity of the CD4 (cid:1) T cell response if CTLA-4 was blocking during priming. Thus, the T cell response was generated to-ward the constellation of chemically dominant and subdomi-nant epitopes as a whole, and did not discriminate among them based on their relative abundance. The Journal of Immunology, 2002, 169: 2832–2836.