Expression patterns of MHC class II genes in rabbit tissues indicate close homology to human counterparts

Genomic clones corresponding to five distinct major histocompatibility complex class II alpha-chains have been described for the rabbit; four of these encode complete, potentially functional alpha-chains. Hybridization analysis and preliminary sequence analysis indicate that one of these clones is structurally related to HLA-DP alpha, one to -DR alpha, one to -DQ alpha and one to -DZ alpha. Probes specific for the four class II genes were used to screen RNA samples from normal rabbit tissues to determine which of these genes are transcribed and whether expression of any particular gene is tissue specific. All four of the genes are transcribed, but there are variations in the levels of expression, in tissue distribution, and in transcript size. The highest levels of RLA-DR alpha, -DQ alpha, and -DP alpha transcription were found in lymphoid tissues. Lower levels of transcription were also detectable in several nonlymphoid tissues. Transcripts observed were about 1.3 kb, a size expected for these class II alpha-chain genes based on experience with their human homologues. The RLA-DZ alpha probe corresponding to HLA-DZ alpha hybridized weakly with a band of 3.6 kb; its expression could be detected only in lymphoid tissues. The size of the DZ alpha transcript, its tissue distribution, and partial sequence data confirm its homology with the human gene DZ alpha. In blots of total cellular RNA, a probe for a recently described human beta-chain, DO beta, hybridized to a transcript of about 1.3 kb in lymphoid tissues. These data indicate that RNA transcripts corresponding to all HLA class II loci described to date can be detected in rabbit tissues.