INTRACELLULAR LOCATION OF CYSTEINE TRANSPORT ACTIVITY CORRELATES WITHPRODUCTIVE PROCESSING OF ANTIGEN DISULFIDE

Activation of CD4(+) T cells requires processing of exogenous protein antigens by antigen-presenting cells (APC). A macrophage hybridoma and B cell lymphoma were comparable in their ability to process hen egg l ysozyme (HEL), which involves reduction of its disulfide bonds. The in tracellular levels of cysteine and glutathione, major physiological th iols, based on protein content were similar within these cell lines. I n addition, the cysteine transport pathway in viable cells was assesse d by S-35-cystine uptake. For macrophages, the majority of the radioac tivity resided in high density subcellular fractions of Percoll gradie nts that comigrated with lysosomal beta-galactosidase (beta-gal). Besi des the lysosomes, low density fractions cosedimenting with endosomes incorporated the radiolabel in the B cells. Both peaks of radioactivit y disappeared when the B cells were incubated with unlabeled carboxyme thyl-cysteine (CM-cysteine), a specific competitor of the plasma membr ane CC transport system. The distinct gradient profiles of radiolabel uptake in the cells correlated with a difference in their capacity to process the transferrin-lysozyme conjugate (TF-HEL). TF-HEL was signif icantly more stimulatory than HEL in inducing a HEL-specific T cell re sponse with the B cells as the APC. However, the potencies of TF-HEL a nd HEL were similar when the macrophages were the APC. Thus, the intra cellular location of cysteine transport activity may be cell lineage-d ependent, and its presence may, in part, determine whether an organell e is a productive site of processing antigens with disulfide bonds tha t is necessary for CD4(+) cell activation. (C) 1996 Wiley-Liss, Inc.