Bulk purification of a naturally occurring soluble form of RT1-A class I major histocompatibility complex antigens from DA rat liver, and studies of specific immunosuppression.

We describe the bulk purification of a water-soluble form of RT1-A class I MHC antigens from aqueous extracts of DA liver. Using a combination of monoclonal antibody affinity, lentil lectin affinity, and gel permeation chromatography, we were able to obtain large quantities of pure water-soluble RT1-A antigens. Typically, from 40 DA livers, 0.5 mg of pure antigen with antigen activity equivalent to 7 X 10(9) nucleated DA spleen cells was obtained. The water-soluble RT1-A molecule had a discrete heavy chain of 40 kD, linked noncovalently to beta 2 microglobulin. The heavy chain of the water-soluble RT1-A molecule was 5 kD smaller than the membrane-bound form of RT1-A from DA liver membranes. The smaller molecule probably represents a secreted form of RT1-A class I molecules that lack the transmembrane domain (exon 5). Large quantities of this water-soluble RT1-A class I antigen from the DA strain, given intravenously to PVG recipients of DA cardiac allografts by a variety of protocols, did not have any effect on graft survival. The fairly ready availability of milligram quantities of pure class I transplantation antigens should be of considerable value for studies in transplantation.