Immunological and biochemical characteristics of the Qa-2 murine nonclassical histocompatibility class 1
antigen expressed on
tumor cells derived from H-2k (Qa-2-) mice were studied. It was found that the
Qa-2 antigen on normal H-2b lymphocytes reacted with Qa-2-specific
monoclonal antibodies (mAbs) 34-1.2, 59 (both specific to the alpha 1/alpha 2 region) and 141-15.8 (specific to the alpha 3 domain), and the
Qa-2 antigen on H-2k
tumor cells (Qa-2k antigen) reacted with mAbs 59 and 141-15.8, but not with 34-1.2. The normal
Qa-2 antigen was susceptible to treatment with
phosphatidylinositol-specific phospholipase C, but the Qa-2k
antigen was insensitive to it. By Northern hybridization, polymerase chain reaction (PCR) studies on
cDNA, Southern hybridization, Western blotting, and nucleotide sequence analysis, the Q5k gene was identified as the gene encoding the Qa-2k
antigen expressed on BW5147
lymphoma cells derived from a mouse of AKR strain (H-2k, Qa-2-). The nucleotide sequence of PCR-amplified BW5147 Q5k
cDNA showed complete agreement with the reported sequence of exons 1-5 of the Q5k gene of C3H/He. It also showed complete deletion of the region corresponding to exons 6 and 7, and a very short coding region in exon 8, resulting in very short cytoplasmic domain of the product compared with regular class 1
antigens. These characteristics were expected from the reported Q5k genomic sequence. These results revealed that the Qa-2k
antigen was distinct from the normal
Qa-2 antigen expressed on H-2b lymphocytes although it cross-reacted with some Qa-2-specific mAbs.