Biochemical characterization of Ia alloantigens in guinea pigs. I. Synthesis of Ia antigens by subsets enriched for B cells, T cells, or macrophages.

Peritoneal exudate cells from immune guinea pigs consist primarily of T lymphocytes (PEL) and M phi. After selection of PEL from animals immunized with ovalbumin by culture on specific antigen-pulsed syngeneic M phi, recovered T cells (selected PEL) are 75 to 95% Ia+ by both cytotoxicity and immunofluorescent analysis on the FACS using alloantisera to Ia from guinea pigs or mice. The subunit structure of the Ia molecules on T cells is similar to that of Ia molecules obtained from B cells, as determined by radiolabeling, immunoprecipitation, and analysis of gels. Incorporation of labeled amino acids into Ia by selected PEL was shown to be due to T cells because of the lack of effect of depletion of Ig+ cells, the elimination of incorporation with a monoclonal anti-lymphocyte antibody, and the negligible increase in radioactive Ia after addition of large numbers of peritoneal exudate M phi. Furthermore, when F1 (2 x 3) PEL are selected on parental M phi, the selected PEL express both parental (2 and 13) Ia specificities, which suggests that the Ia molecules are not adsorbed by T cells after their release by M phi. Evidence that synthesis by splenocytes is due to B cells was obtained by the results of deletion experiments with alpha Ig and C. Similarly, synthesis of Ia by populations of pulmonary alveolar M phi, which contain greater than 98% M phi as judged by morphology, adherence, and latex ingestion, was demonstrated to be due to M phi because of the lack of effect of removing T and B cells.