We have previously demonstrated that anti-H-43a CTL response of H-43b responder mice was exclusively restricted by self H-2Kb (Kb) but not by the other nine self MHC class I alleles from independent origins, i.e., Kbml,d,k,s and Db,d,k,q,s. In the present study, we verified that Kf,q,r and Df,r alleles could also not serve as restricting class I elements in the CTL response to H-43a alloantigen. Another notable observation made in the earlier study was the fact that, in H-43 incompatibility of the alternative combination, H-43a mice were incapable of generating CTL activity against H-43b alloantigen. However, by means of employing new in vivo immunization procedures, we discovered that some but not all genetically identical H-43a responder mice could mount anti-H-43b CTL response restricted by self Kb. Again, no anti-H-43b CTL activity could be generated in the context of self Kk, Kj, Db or Dk molecules. Although the number of class I alleles we examined is still limited, these results indicate that antigenic fragments derived from the processed H-43a and H-43b alloantigens possess an indistinguishable epitope (agretope), and that such agretope either interacts only with the privileged Kb molecules or allows to bestow the immunogenic conformation of allodeterminants on the fragments solely in the context of the restricting Kb element.

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