Biochemical characterization of Ia alloantigens in guinea pigs. II. Comparative peptide mapping of Ia antigens from B cells, T cells, and Mφ

Radioactive Ia.4 molecules were prepared from ³H- or ¹⁴C-labeled splenocytes, selected PEL, or bronchoalveolar macrophages (Mφ). Studies in the accompanying paper indicated that incorporation into Ia.4 in these 3 populations is due to B cells, T cells, and Mφ, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to isolate the 58,000 m.w. form of Ia.4. The eluted molecule was then reduced, and the resultant α and β subunits were isolated by a second separation on SDS-PAGE. α (or β) chains frowm 1 population labeled with ³H-amino acids was mixed with α (or β) chains obtained from a population representing a different cell type that was labled with ¹⁴C-amino acids and the mixture was digested with trypsin. Double-label (³H/¹⁴C) comparative peptide mapping was performed using high-pressure liquid chromatography to separate the peptides. Eighteen to 20 peaks of radioactivity were resolved from α chains, and 12 to 15 from β chains. No reproducible differences were observed when comparing α or β chains of T cells and Mφ, those of B cells and Mφ. These results indicate that the primary structure of Ia.4 molecules is identical on the 3 cell types in question. The implications of having a T cell bearing the same Ia that it recognizes on a Mφ in conjunction with antigen is discussed.