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 pr otein in the context of I-A(q) molecules, we have generated hybrid ant igen-presenting cells (APC) by fusion of B lymphoma (A20 and M12) cell s with CII-primed spleen cells from DBA/1 mice. Efficient presentation of CII by these APC to specific T cell hybridomas required prior clea vage of the antigen and intracellular handling of the peptides. Inhibi tion of protein transport by brefeldin A prevented the presentation of oil 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 a lymphomas to leupeptin, a protease inhibitor, induced a dose-dependent increase of CII-specific T cell r esponse, while abrogating the I-A(q)-restricted presentation of ovalbu min. The enhancing effect of leupeptin was also observed when immune B cells were used as APC. In contrast, leupeptin inhibited the presenta tion 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) chai n revealed that leupeptin did not affect the Ii chain processing or th e formation of stable class II dimers. The stimulatory effect of leupe ptin observed on oil presentation suggests that leupeptin protects CII epitopes by interfering with proteases involved in the intracellular degradation of CII.