Proteins encoded by genes in the MHC are highly polymorphic. For class II proteins the highest level of polymorphism is found in distinct regions of variability, notably in the membrane-distal domains. To investigate the role of such residues in antigen presentation, we have tested cells transfected with wild-type or mutant I-Ak beta chains for their ability to present the NH2-terminal peptide of myelin basic protein to a panel of T cell clones. We were unable to detect a gross effect on peptide binding, in that all of the mutant cell lines presented antigen to at least one of the cloned T cells. However, the results imply that the more NH2-terminal residues, particularly 12 and 14, are involved in peptide interactions. Mutations at these residues presented antigen only at high antigen concentrations. Furthermore, residues of the more COOH-terminal regions appear to determine TCR interactions. Mutations in the predicted alpha-helical regions of the beta chain affected antigen presentation without abolishing peptide binding.
The role of polymorphic I-Ak beta chain residues in presentation of a peptide from myelin basic protein.
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C B Davis, J M Buerstedde, D J McKean, P P Jones, H O McDevitt, D C Wraith; The role of polymorphic I-Ak beta chain residues in presentation of a peptide from myelin basic protein.. J Exp Med 1 June 1989; 169 (6): 2239–2244. doi: https://doi.org/10.1084/jem.169.6.2239
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