Presentation of the Goodpasture Autoantigen to CD4 T Cells Is Influenced More by Processing Constraints Than by HLA Class II Peptide Binding Preferences

Abstract

Class II molecules are believed to influence immune responses by selectively binding antigen-derived peptides for recognition by T cells. In Goodpasture's (antiglomerular basement membrane) disease, autoimmunity to the NC1 domain of the ␣3-chain of type IV collagen (␣3(IV)NC1) is strongly associated with HLA-DR15. We have examined the influence of the peptide binding preferences of DR15 molecules on the selection of ␣3(IV)NC1-derived peptides displayed bound to DR15 molecules on the surface of ␣3(IV)NC1-pulsed DR15-homozygous Epstein-Barr virus-transformed human B cells. The preferences of DR15 molecules were investigated using a panel of 24 overlapping peptides spanning the sequence of ␣3(IV)NC1. The ␣3(IV)NC1-derived peptides selected for display to T cells were determined by biochemical analysis as reported previously (Phelps, R. G., Turner, A. N., and Rees, A. J. (1996) J. Biol. Chem. 271, 18549 -18553).Three nested sets of naturally presented ␣3(IV)NC1 peptides were detectable bound to DR15 molecules. Peptides representative of each nested set bound to DR15 molecules, but almost two-thirds of the ␣3(IV)NC1 peptides studied had as good or better DR15 affinity than those identified as naturally processed. Thus ␣3(IV)NC1 presentation to T cells is determined more by "processing factors" than by the preferences of relatively indiscriminate DR15 molecules. The results have important implications for the use of class II peptide binding data to aid identification of potential T cell epitopes, especially for antigens which, like ␣3(IV)NC1, contain many sequences able to bind class II molecules. Antigen presenting cells (APC)1 potentially exert a profound influence on immune responses, including those to self antigens, because they regulate the way T cells recognize antigens. CD4 T cells recognize antigens in the form of processed peptides presented bound to MHC class II molecules on the surface of class II positive APC types (1, 2). These include cells important in the initiation of immune responses, such as dendritic cells, B cells, and macrophages, and cells important in regulating the T cell repertoire and self-tolerance, such as thymic epithelia. How APC select antigen-derived peptides for display to T cells therefore not only constrains the peptide specificity of responding T cells, but also influences the repertoire of T cells available to mount immune responses. Furthermore, the way APC present antigens may determine the immunodominant T cell response, which at least for some exogenous antigens is directed at the antigen-derived peptide displayed at the highest level (3). There is therefore great interest in understanding how APC generate antigen-derived peptides and make a selection for display to T cells, both as an approach to identifying T cell epitopes for specific immune modulation and toward understanding the basic biology of immune responses.APC, like many cell types, internalize extracellular proteins into their endosomal/lysosomal pathway where denaturing (low pH and reducing) conditions promote th...

Antibodies against Linear Epitopes on the Goodpasture Autoantigen and Kidney Injury

“…The recognition for P16 was identified to be associated with higher concentration of serum creatinine on diagnosis and was a poor prognostic indicator for renal outcome. We noticed that P16 contained one of the core sequences on a3(IV)NC1 that could be naturally processed and presented by antigen presenting cells (25,30). It is likely that these autoreactive B cells against P16 may serve as professional antigen presenting cells to stimulate autoreactive T cells.…”

“…Previous studies have demonstrated that P14 contained the core sequence with highest predicted binding affinity with HLA-DR15 (25,26), which was proven to be the genetic marker for susceptibility to anti-GBM disease. The finding that a mutual T and B cell epitope exists in human anti-GBM disease, in accordance with the results from animal models, favors the hypothesis that certain nephrogenic linear epitopes might initiate the disease by stimulating both humoral and cellular responses.…”

T Cells in Crescentic Glomerulonephritis

“…T cells from patients with acute disease react to a limited number of peptides of ␣3(IV)NC1 (␣3 71 to 90 and ␣3 131 to 150), suggesting that these are the likely natural immunodominant peptides (63). However, these are not the peptides that induce the strongest responses in T cells from patients with anti-GBM GN when presented by DR15 on Epstein-Barr virus-transformed human B cells, suggesting that factors other T cell receptor affinity determine selection of immunodominant autoreactive epitopes (64). The cytokine profile of autoreactive ␣3(IV)NC1 T cells from patients in the acute phase of the disease is Th1 predominant (producing IFN-␥); whereas during resolution of disease, IL-10 production is predominant (65).…”

Healthy Individuals Have Goodpasture Autoantigen-Reactive T Cells

“…In the case of DR15-bearing individuals it is possible to test the hypothesis further because we have reported relative binding data for ␣3(IV)NC1 peptides, 15 which can be refined to identify probable epitopes using published binding algorithms.…”