A 38 year old woman presents with fever of 103degF, hypotension, confusion and a diffuse, erythematous rash. She had uncontrollable epistaxis for which a nasal pack was placed 3 days ago. What is the likely mechanism of action of the microbial toxin that has caused her current illness?

This woman presented with fever, hypotension and a diffuse rash 3 days after a nasal packing was done. This is characteristic of toxic shock syndrome - commonly caused by Staphylococcal Toxic Shock Syndrome Toxin - 1 (TSST -1), which is a superantigen. Superantigens act by causing polyclonal activation of T cells - Activate large number of T cells irrespective of their antigen specificity. In contrast to regular antigens which bind to the binding groove on T Cells, superantigens bind outside the groove directly to the lateral aspect of TCR b chain. This leads to massive release of cytokines and polyclonal activation of T cells: Clinically, this manifests as fever, hypotension, and skin exfoliation. Examples of organisms which produce superantigens: Bacterial Staphylococcus aureus Streptococcal toxin Mycoplasma ahritidis mitogen 1 Yersinia enterocolitica Yersinia pseudotuberculosis Viral Epstein-Barr virus (EBV) Cytomegalovirus (CMV) Rabies nucleocaspid HIV-encoded negative regulatory factor. Fungal Malassezia furfur Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition