Processing of viable group A streptococci leads to major histocompatibility complex class II presentation of T cell epitopes from the major protective antigen

Abstract

We have previously mapped major histocompatibility complex (MHC) class II-restricted T cell epitopes of the surface M protein of type 5 group A streptococci (M5) and show here that two out of four epitopes investigated were efficiently processed during incubation of viable streptococci with spleen cells for presentation to M5-specific murine T cell clones. Viable streptococci were processed more efficiently than heat-killed bacteria suggesting that secreted virulence factors of streptococci do not obstruct processing of streptococcal antigens in the dose range used. Epitopes from different regions of M5 could be ranked according to the efficiency with which they were processed, which may contribute to their relative immunodominance. It was further demonstrated that T cell clones specific for M5 308-319, an epitope from the M type conserved carboxy-terminal half of M5, cross-reacted between M5, M6 and M12, but not M49, streptococci. Helper T cell epitopes which are shared between streptococcal M types and are presented by MHC class II molecules on antigen-presenting cells after processing of viable streptococci could be particularly useful in the design of multivalent streptococcal vaccines.

The route of bacterial uptake by macrophages influences the repertoire of epitopes presented to CD4 T cells

“…We studied the mechanisms of uptake of viable S. pyogenes by macrophages for presentation of T cell epitopes M5 [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] and M5 308-319 from the surface M5 protein to T cell hybridomas. We showed that disruption of actin polymerization blocked presentation of both epitopes from viable S. pyogenes consistent with the complete inhibition of internalization of S. pyogenes as judged from electron microscopy studies.…”

“…J774A.1 macrophages were pulsed with viable S. pyogenes or synthetic peptides in the presence of metabolic inhibitors to study the mechanisms of uptake of S. pyogenes for presentation of two M5 protein T cell epitopes, M5 [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] and M5 308-319 . First, we treated macrophages with cytochalasin D, which prevents F-actin polymerization, Fig.…”

“…The effect of inhibitors of bacterial uptake on presentation of two M5 protein-specific T cell epitopes by J774A.1 macrophages. Cells were treated with cytochalasin D (A), monodansylcadaverine (B), amiloride (C), or dimethylamiloride (D) in the dose ranges shown, and pulsed with 3×10 6 viable S. pyogenes (squares) or synthetic peptides (circles) before antigen-presentation assay with T cell hybridomas HX17, specific for M5 [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] (filled symbols), and HY2, specific for M5 308-319 (empty symbols). T cell hybridoma responses were measured as CTLL-2 proliferation in cpm (± SEM) in the presence of T cell hybridoma supernatants.…”

“…1D), both of which inhibit membrane Na + /K + -ATPase, membrane ruffling and mac-ropinocytosis [13,14]. Both inhibitors blocked presentation of M5 308-319 , but had no effect on M5 [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] (Fig. 1C, D), suggesting the involvement of macropinocytosis for presentation of only one of the two epitopes.…”

Phagocytic processing of two M protein T-cell epitopes from viable group A streptococci

“…Another epitope, M5/308-3 19/Ad, provided help for induction of peptide-specific antibodies, and was presented from at least three different M types (M5, M6 and M12) of S. pyogenes. In addition, both epitopes were efficiently processed from viable bacteria and the soluble M5 protein for presentation to CD4+ T-cell clones [3,4]. Together this data suggests that these epitopes may be useful for development of streptococcal vaccines.…”