Histocompatibility typing by cellular radioimmunoassay

Abstract

A quantitative cellular radioimmunoassay (CRIA) for histocompatibility typing is described. Chicken red blood cells (RBC) were incubated in microtiter plates with specific anti-MHC (B) alloantisera and the alloantibody bound measured indirectly by a second binding step with¹²⁵I-labeled rabbit anti-chicken IgG. The assay is objective, highly consistent, and three to four orders of magnitude more sensitive than conventional hemagglutination assays. The new CRIA was used to detect minor subpopulations of cells in artificial cell mixtures; as few as 1% of relevant cells were easily detected. Erythrocyte chimerism was induced following the injection of B²/B² chicken embryos with B¹⁵/B²¹ embryonic stem cells. Five weeks after hatching, erythrocyte chimerism was precisely quantitated by comparing the reaction of RBC from the putative chimeras with artificial cell mixtures using specific anti-B₁₅/B₂₁ alloantisera. The percent varied from 13–40% in 13 chimeric animals. The new CRIA was also used for the sensitive detection of tumor-specific antigens on a T-cell lymphoma. An unexpected finding was that anti-B₁₅ alloantibody bound almost as well to B¹⁵/B²¹ heterozygous RBC as to B¹⁵/B¹⁵ homozygous cells, suggesting that either the concentration or the steric arrangement of B₁₅ alloantigen at the erythrocyte surface may not conform to conventional expectations.