AN ENZYME-IMMUNOASSAY FOR RAT SOLUBLE MHC CLASS-I MOLECULES (RT1(A)) AND THE RELEASE OF SOLUBLE CLASS-I FROM MITOGENICALLY STIMULATED MONONUCLEAR-CELLS

Soluble MHC class I antigens can be detected in the serum of humans an d various animals and appear in the circulation shortly after liver tr ansplantation. The precise role of these antigens is currently uncerta in, but soluble MHC class I may be involved in immunomodulation. We ha ve developed an enzyme linked immunosorbent assay for soluble rat MHC class I (RT1(a)) molecules and monitored the kinetics of antigen relea se following in vitro stimulation of splenic mononuclear cells. A 4 da y DA splenocyte Con A supernatant provided a source of soluble class I antigens and was arbitrarily assigned a concentration of 1000 units/m l. Ninety six well plates were coated with a rat RT1(a)-specific mAb ( MN4-91-6) and soluble class I binding was detected using a biotinylate d mAb reactive with a monomorphic region of the rat MHC class I molecu le (OX18) followed by a streptavidin-alkaline phosphatase conjugate an d substrate. The intra- and interassay variations were typically less than 5% and 10% respectively, to give a working range for the assay of between 62.5 and 1000 units/ml. Mitogenic stimulation led to a progre ssive increase in soluble class I levels in culture supernatants. This assay will be valuable in differentiating recipient and graft respons es following experimental organ transplantation.