CHARACTERIZATION OF FIBROBLASTS WITH A UNIQUE DEFECT IN PROCESSING ANTIGENS WITH DISULFIDE BONDS

A Chinese hamster ovary (CHO) fibroblast, transfected with murine MHC class II genes, inefficiently stimulated CD4(+) Th cells specific for OVA, hen egg lysozyme (HEL), and pork insulin which contain disulfide bonds. However, the fibroblasts elicited a T cell response to lambda r epressor, which lacks disulfide bonds, and efficiently presented synth etic peptides. A somatic cell hybrid WALC, generated by fusing the ham ster fibroblast with a murine L cell fibroblast, very efficiently proc essed OVA and HEL, suggesting that impaired processing was genetically complemented and was a recessive trait. The hamster fibroblasts were capable of processing two distinct denatured forms of OVA and carboxym ethylated HEL, either as effectively or more efficiently than the B ly mphoma cell. The CHO cells also displayed diminished disulfide reducti on of an endocytosed [I-125]tyramine linked to poly-(D-lysine) through a disulfide spacer compared with that of the cell hybrid, providing d irect evidence for defective reductive cleavage by the CHO cells. Dimi nished aspartic acid-mediated proteolysis of Ag could not account for the phenotype, because cell lysates and separated organelles from the fibroblast possessed higher acidic aspartyl proteolytic activity than lysates and organelles from a B lymphoma cell. Thus, CHO cells exhibit a defect in processing Ag with disulfide bonds which is consistent wi th the impaired intracellular reduction of the disulfide bonds in endo cytosed macromolecules.