THE CRYPTIC HLA-DQA2 (DX-ALPHA) GENE IS EXPRESSED IN HUMAN B-CELL LINES

Although there are two gene pairs in the HLA-DQ region, DQA1/B1 and DQA2/B2, the latter pair have never been found to be expressed. The DQA2 and DQB2 genes appear to be normal at the DNA sequence level, there being no indication that they should be pseudogenes, and normal splicing occurs when DQA2 is included in a retroviral vector. The putative amino acid sequences of DQA2 and DQB2 have been nearly invariant, raising the questions of how these genes have been maintained normal-appearing and nearly monomorphic if they are not expressed and, if they are expressed, in what cell types are they expressed. We present Northern blot, nuclease protection assay, and mRNA sequence data that demonstrate the existence of spliced DQA2 mRNA in human B lymphoblastoid cell lines. In contrast, we found no evidence of DQB2 mRNA in the same cell lines, nor of DQA2 mRNA in the monocyte line U937 or in activated T cells.