Specific role for cathepsin S in the generation of antigenic peptidesin vivo

Abstract

To address the role of different proteases in degradation of antigen destined for MHC class II‐restricted presentation, we generated cathepsin‐deficient mice carrying a transgenic B cell receptor (BCR) specific for hen egg lysozyme (HEL). We demonstrate that degradation of HEL in B lymphocytes is highly processive and does not result in discrete processing intermediates. Moreover, degradation of HEL does not require initial unlocking of the antigen by any of the cathepsins tested. Using mass spectrometry and microsequencing, we show that all major cathepsins (CatS, CatL, CatB, and CatD) digest HEL in vitro with considerable redundancy, although some preferential cleavages are evident. These observations have a functional correlate: when triggered by cathepsin S‐deficient antigen‐presenting cells, T cells that recognize different HEL epitopes fail to present two HEL‐derived epitopes, while a third epitope is presented independently of the activity of cysteine proteases. We conclude that the proteolytic processing machinery is redundant, and that several proteases can substitute for each other to degrade a given antigen. However, a certain degree of proteolytic specificity is demonstrable for the generation of particular epitopes, notably by CatS.

Aod1Controlling Day 3 Thymectomy-Induced Autoimmune Ovarian Dysgenesis in Mice Encompasses Two Linked Quantitative Trait Loci with Opposing Allelic Effects on Disease Susceptibility

“…Trfr (transferrin receptor or Cd71; 21.2 cM) expression is down-regulated in adult T cell development as well as in ontogeny before the TCR ␣␤ appears on the cell surface of the thymocyte and serves as a marker of immature, proliferating T cells (57). Stfa1, Stfa2, and Stfa3 (stefin A1, A2, and A3) at 22.85 cM are inhibitors of cysteine endo-and exopeptidases (58) such as cathepsin L and S that are involved in Ag processing (59,60). Most importantly, cathepsin S inhibitors have been shown to prevent autoantigen presentation in vitro, while in vivo treatment blocks lymphocytic infiltration into the salivary and lacrimal glands, abrogates autoantibody production, and promotes the recovery from autoimmune manifestations in D3Tx NFS/sld mice (61).…”

Diverse regulatory roles for lysosomal proteases in the immune response

“…At least in vitro, loss or inhibition of single enzymes can impact, positively or negatively, on CD4 1 T-cell epitope generation and/or on the spectrum of elutable MHC class II bound peptides (reviewed in [26]). Individual enzymes present in lysosomal extracts frequently dominate processing of specific antigens in vitro and blockade of those enzymes can reduce presentation of T-cell epitopes [27,28]. This requirement may be for initial ''unlocking'' cleavages [29, 30] or downstream processing events [28].…”

“…Individual enzymes present in lysosomal extracts frequently dominate processing of specific antigens in vitro and blockade of those enzymes can reduce presentation of T-cell epitopes [27,28]. This requirement may be for initial ''unlocking'' cleavages [29, 30] or downstream processing events [28].…”

“…Individual enzymes present in lysosomal extracts frequently dominate processing of specific antigens in vitro and blockade of those enzymes can reduce presentation of T-cell epitopes [27,28]. This requirement may be for initial ''unlocking'' cleavages [29, 30] or downstream processing events [28].Loss or inhibition of cathepsin E has been reported to compromise processing and presentation of antigens such as ovalbumin, myoglobin and tetanus toxin [31,32]. However, contrasting results were seen when macrophages and DC were compared, as cathepsin E null DC showed an enhanced presentation of ovalbumin, a result attributed to increased phagocytosis and elevated expression of co-stimulatory molecules [31].…”

Lowering the affinity between antigen and the B cell receptor can enhance antigen presentation

“…The mutant and wild-type lysozymes could therefore be compared using the same BCR. The mutations are unlikely to affect processing directly, as the altered residues are not involved in the proteolysis of HEL by any of a range of enzymes recently tested [26]. Furthermore, the proteolysis in association with the HyHEL-10 BCR was shown to involve an overlapping array of largely redundant enzymatic activities [26].…”