MAFA-L, AN ITIM-CONTAINING RECEPTOR ENCODED BY THE HUMAN NK CELL GENE-COMPLEX AND EXPRESSED BY BASOPHILS AND NK CELLS

The natural killer cell gene complex on human chromosome 12p12-13 enco des several C-type lectin receptor genes expressed by NK cells and oth er hematopoietic cells. We have identified a novel receptor gene in th is region encoding a putative type II transmembrane glycoprotein. The product is 54 % identical to the rat mast cell function-associated ant igen (MAFA), which inhibits mast cell activation by IgE. The human MAF A-like receptor (MAFA-L) and the rat MAFA protein are expressed by bas ophils and both have an immunoreceptor tyrosine-based inhibitory motif in the cytoplasmic tail, consistent with an inhibitory role in basoph il activation. Unlike rat MAFA, expression of the MAFA-L gene is not l imited to mast cells and basophils. In common with other genes in the NK cell gene complex MAFA-L is also expressed by natural killer cells as well as the monocyte-like cell-line U937. Expression in NK cells is restricted to peripheral blood NK cells, decidual NK cells do not exp ress MAFA-L. While MAFA-L and rat MAFA might have a similar role in ba sophils, the expression of MAFA-L in other cell types implies addition al functions for this molecule. The presence of the MAFA-L gene in the human NK cell complex indicates that this locus encodes C-type lectin receptors expressed by a variety of cells important in host defense.