Tissue-specific expression of an unusual H-2 (class I)-related gene

Sequence analysis of mouse H-2 cDNA clones has suggested the existence of an unusual class of H-2 (class I)-related antigens that, unlike the classical membrane-associated molecules, retains only the extracellular portion and is likely to be secreted. The expression of this class of H-2-related mRNA is tissue restricted; it is detectable in liver but not in brain, kidney, testis, thymus, or spleen. In the liver, its accumulation represents about one-fourth of all the H-2 (class I)-specific transcripts. This class of transcripts is present in mice of different inbred strains, but the level of expression differs markedly among them. A model is presented in which such a soluble form of the H-2 antigen would play the role of a blocking factor in maintaining peripheral inhibition of H-2 recognition. This would ensure tolerance of the H-2 molecule as a self antigen while permitting it to act as a guidance molecule for the associative recognition of viral and tumor antigens by cytotoxic T cells.