DEFECTIVE ANTIGEN-PROCESSING CORRELATES WITH A LOW-LEVEL OF INTRACELLULAR GLUTATHIONE

Previously we reported that Chinese hamster ovary (CHO) cells transfec ted with murine mouse major histocompatibility complex class II genes, exhibit a unique antigen (Ag) processing defect whereby these cells a re impaired in processing only Ag with disulfide bonds. Here, we exami ned various aspects of the intracellular reducing environment in the C HO cells to understand the underlying mechanism causing the defect. A cell hybrid generated by the fusion of CHO cells and L cell fibroblast s was used for comparison due to their competency in processing Ag. Th e transport pathway of cysteine within the CHO cells appeared normal. However, these cells had a significantly lower level of glutathione, a major physiological reducing thiol, compared to the cell hybrid. Trea tment of the CHO cells with N-acetyl-L-cysteine did not augment their glutathione content nor their ability to process Ag. When the cell hyb rid was treated with L-buthionine-(S,R)-sulfoximine (BSO), which signi ficantly decreased their glutathione level, the hybrid poorly processe d hen egg lysozyme (HEL) and ovalbumin, which have disulfide bonds. In contrast, BSO treatment did not affect the capacity of the hybrid to process pigeon cytochrome c and carboxymethylated HEL, which lack disu lfide bonds. Therefore, low intracellular glutathione levels in antige n-presenting cells correlated with defective processing of Ag with dis ulfide bonds, indicating that this thiol may be a critical factor in r egulating productive Ag processing.