Expression of L cells of transfected class I genes from the mouse major histocompatibility complex

One of the major surprises of the molecular analysis of major histocompatibility complex (MHC) genes is the large number of class I (K/D)-related sequences in the genome. Both restriction fragment length polymorphisms and cosmid cloning experiments showed them all to be closely linked to the MHC. Until now little information was available concerning either their expression or recognition by the immune system. Here we report that these non-K/D genes can provoke antibody responses and be recognized by cytolytic T cells. Immunization of C3H mice with L cells transfected with class I genomic clones resulted in antisera that reacted preferentially with cells from strain B10.P (the gene donor). Thus, these genes can be expressed by L cells. These products were recognized by cytolytic T cells produced by mixed lymphocyte culture with B10.P stimulators. One gene, represented in clone λ3a, was chosen for further analysis. A restriction fragment length polymorphism, detected between B10.P (K(P)D(P)) and B10.F(14R) (K(b)D(P)) and between B10 (K(b)D(b)) and B10.F(13R) (K(P)D(b)), has enabled us to map the λ3a sequence to the D or Tla region. Restriction endonuclease mapping of the λ3a clone shows that the gene is intact and that, although many restriction sites are conserved, the gene in λ3a differs from other class I genes. When the λ3a clone was transfected into mouse L cells, a new product was expressed. Cells expressing this product (designated L3a cells) were killed by primary D-end-reactive, allospecific cytolytic T lymphocytes. The L3a cells were unreactive with monoclonal antibodies specific for the K(p),D(p),Qa-2, Tla.3, and Tla.5 molecules.