Review Question - QID 101031

This patient has toxic shock syndrome due to preformed Staph aureus toxin TSST-1. This toxin binds to the variable beta portion of the T-cell receptor as a superantigen.

Superantigens are microbial molecules that can activate T cells in nonspecific fashion. They bind to certain domains on MHC class II molecules of macrophages and to certain domains on the variable beta chain on the T cell receptor, forming a bridge between the two cells. A superantigen can bind to T-cell receptors from a number of different T cells, as long as they share similar amino acid sequences in the variable portion of the beta-chain.

Bamberger and Boyd review management of S. aureus infections. With regard to toxic shock syndrome, they advise timely removal of the S. aureus source and use of a beta-lactamase–resistant antistaphylococcal antibiotic. Clindamycin, which has the potential of reducing toxin production, is also recommended.

Uchiyama et al. conducted one of the earliest experiments that linked TSST-1 to MHC Class II molecules on T-cells. They attached radioactive markers on TSST-1 and noticed T-cell proliferation via IL-2, but not in other types of immune cells. Via gel electropheresis, they then identified MHC Class II in association with TSST-1.

Illustration A depicts a CD4+ T-cell becoming activated by an antigen presenting cell. Note the antigen:MHC II complex recognition by the T-cell receptor.

Incorrect Answers:
Answer 1: CD3 (composed of 2 CD3-epsilon, 1 CD3-delta, and 1 CD3-gamma) is a part of the T-cell receptor complex.
Answers 2 and 3: As described above, CD4 helper T-cells bind to an MHC complex containing MHC class II and to B7 on antigen presenting cells during activation.
Answer 5: As described above, CD4 helper T-cells bind to IL-2 to promote proliferation, not the Fas ligand. The Fas ligand is involved in the apoptosis cascade.