A mutation of F47 to A in staphylococcus enterotoxin A activates the T-cell receptor Vbeta repertoire in vivo.
The bacterial superantigen staphylococcal enterotoxin A (SEA) binds with high affinity to major histocompatibility complex (MHC) class II molecules and subsequently activates T cells bearing particular T-cell receptor (TCR) Vbeta chains. Structural and mutational studies have defined two distinct MHC class II binding sites located in the N-terminal and C-terminal domains of SEA. The N-terminal F47 amino acid is critically involved in a low-affinity interaction to the MHC class II alpha-chain, while the C-terminal residues H187, H225, and D227 coordinate a Zn2+ ion and bind with moderate affinity to the beta-chain. In order to analyze whether the SEA-MHC class II alpha-chain interaction plays a role in dictating the in vivo repertoire of T-cell subsets, we studied distinct Vbeta populations after stimulation with wild-type SEA [SEA(wt)] and SEA with an F47A mutation [SEA(F47A)]. Injections of SEA(wt) in C57BL/6 mice induced cytokine release in serum, strong cytotoxic T-lymphocyte activity, expansion of T-cell subsets, and modulated expression of the T-cell activation antigens CD25, CD11a, CD44, CD62L, and CD69. SEA-reactive TCR Vbeta3+ and Vbeta11+ T cells were activated, while TCR Vbeta8+ T cells remained unaffected. The SEA(F47A) mutant protein induced a weaker T-cell response and failed to induce substantial interleukin-6 production compared to SEA(wt). Notably, SEA(F47A) failed to activate TCR Vbeta11+ T cells, whereas in vivo expansion and modulation of T-cell activation markers on TCR Vbeta3+ T cells were similar to those for SEA(wt). A similar response to SEA(F47A) was seen among CD4+ and CD8+ T cells. Activation of TCR Vbeta3+ and TCR Vbeta11+ T-cell hybridomas confirmed that SEA(F47A) activates TCR Vbeta3+ but not TCR Vbeta11+ T cells. The data support the view that the SEA-N-terminal MHC class II alpha-chain interaction defines a topology that is required for engagement of certain TCR Vbeta chains in vivo.
Rosendahl
A
A
Pharmacia & Upjohn, Lund Research Center, Sweden.
Hansson
J
J
Antonsson
P
P
Sékaly
R P
RP
Kalland
T
T
Dohlsten
M
M
D000818:Animals; D002460:Cell Line; D004768:Enterotoxins / Q000235:genetics / Q000276:immunology*; D005260:Female; D006801:Humans; D007135:Immunoglobulin Variable Region / Q000276:immunology; D016130:Immunophenotyping; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000276:immunology*; D013210:Staphylococcus / Q000276:immunology*; D018089:Superantigens / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology* / Q000382:microbiology
D004768:Enterotoxins; D007135:Immunoglobulin Variable Region; D016693:Receptors, Antigen, T-Cell, alpha-beta; D018089:Superantigens; C026066:enterotoxin A, Staphylococcal