Selective increased presentation of type II collagen by leupeptin

Type II collagen (CII) is an arthritogenic self antigen in DBA/1 (H-2 q ) mice. To analyze the intracellular processing of this fibrillar protein in the context of I-A q molecules, we have generated hybrid antigen-presenting cells (APC) by fusion of B lymphoma (A20 and M12) cells with CII-primed spleen cells from DBA/1 mice. Efficient presentation of CII by these APC to specific T cell hybridomas required prior cleavage of the antigen and intracellular handling of the peptides. Inhibition of protein transport by brefeldin A prevented the presentation of CII peptides to T cell hybridomas, indicating that the intracellular presentation of CII was dependent on neo-synthesis of I-A q molecules. In contrast, exposure of hybrid B lymphomas to leupeptin, a protease inhibitor, induced a dose-dependent increase of CII-specific T cell response, while abrogating the I-A qrestricted presentation of ovalbumin. The enhancing effect of leupeptin was also observed when immune B cells were used as APC. In contrast, leupeptin inhibited the presentation of CII peptides by macrophages or total spleen cells. Pulse-chase analysis of metabolically labeled hybrid APC and immunoprecipitation with antibodies specific for class II molecules or invariant (Ii) chain revealed that leupeptin did not affect the Ii chain processing or the formation of stable class II dimers. The stimulatory effect of leupeptin observed on CII presentation suggests that leupeptin protects CII epitopes by interfering with proteases involved in the intracellular degradation of CII. This drug can block the presentation of endogenous and Second, the Ii chain blocks the loading of peptides onto the class II molecules (13,14). Third, the Ii chain directs the exogenous antigens to MHC-restricted T cells by affecting the intracellular transport of newly synthesized MHC class I transport of class II molecules to an endosomal/lysosomal compartment (15-17). Within the endocytic compartments, and class II molecules (22,23). Leupeptin is known to inhibit the MHC class II presentation pathway. It was reported to the Ii chain is degraded and removed from the class II