EXPRESSION ANALYSIS OF THE SOLUBLE AND MEMBRANE-ASSOCIATED FORMS OF THE INTERLEUKIN-1 RECEPTOR-RELATED T1 PROTEIN IN PRIMARY MAST-CELLS ANDFIBROBLASTS

The murine T1 gene encodes a membrane-bound glycoprotein (T1M) and a s oluble variant (T1S) which represents the ectodomain of the receptor-t ype form. T1 is an orphan receptor belonging to the interleukin-l rece ptor family, Its biological function is currently unknown. We analyze the expression of the two T1 proteins in mast cells and fibroblasts by using a set of monoclonal antibodies (MAb) that specifically recogniz e the extracellular portion of the T1 receptor. To generate anti-T1 MA bs, we immunized Lewis rats with a eukaryotically expressed chimeric p rotein consisting of the T1-receptor ectodomain fused to a human immun oglobulin domain. The two MAbs DJ4 and DJ8 mere shown to specifically detect the murine T1M protein on the surface of primary IL-3-dependent bone marrow-derived mast cells as shown by flow cytometry and immunoh istochemistry, Both antibodies were also capable of immunoprecipitatin g the membrane-associated 110-120 kDa T1M protein from mast cell lysat es, In serum-stimulated but not in quiescent NIH3T3 fibroblasts, DJ4 a nd DJ8 MAbs detected both the soluble T1S protein as a 45-65 kDa band on SDS polyacrylamide gels as well as the membrane-bound 95 kDa T1M pr otein. The T1M protein in fibroblasts was Less abundantly expressed an d exhibited a lower molecular weight than the mast cell-produced T1M, probably as a consequence of different protein glycosylation. The MAbs described here represent highly specific reagents and valuable tools that should facilitate the establishment of the murine T1 protein expr ession pattern thus contributing to the solution of the question of it s function.