Peptide interactions with the Kb antigen recognition site

The ability of OVA-specific H-2Kb-restricted CTL to recognize the defined OVA258-276 peptide in the context of the Kbm mutants and variants of these mutants was examined to determine how specific variations in the Ag recognition site-influenced peptide presentation to these CTL. L cells expressing Kb or Kbm10 were equally capable of presenting the OVA peptide to Kb-restricted, OVA-specific bulk CTL, whereas L cell clones expressing Kbm8 or Kbm1 showed little to no capacity to present this peptide. L cell transfectants expressing Kbm3 and Kbm23 consistently demonstrated an intermediate to low level of presentation to bulk OVA-specific CTL. Dissection of the Kbm8 mutant revealed that cells expressing Kbm8-22 (Tyr----Phe) and/or Kbm8-24 (Glu----Ser) presented the OVA peptide significantly less well than the Kb-presenting molecule. Presentation of OVA by cells expressing Kbm8-23,30 (Met----Ile) (Asp----Asn), Kbm8-23 (Met----Ile), and Kbm8-30 (Asp----Asn) was equivalent to Kb presentation. Another mutation designated as Kbm5, that has a substitution at position 116 (Tyr----Phe), demonstrated an intermediate to high ability to present OVA258-276 to an OVA-specific CTL line. The Kbm3, Kbm11, and Kbm23 mutants were unable to present the OVA peptide to this same CTL line. Dissection of these mutants showed that the substitution at position 77 (Asp----Ser), which is shared by all three mutants, was responsible for their inability to present the peptide. A second Kb-restricted CTL line was able to recognize OVA in the context of the Asp----Ser substitution at position 77. The results of this analysis suggest that the OVA258-276 peptide interacts with multiple regions within the Ag recognition site of the Kb class I protein.