This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology Pa 1 (Immune Response, Antigen-Antibody Reactions, Hypersensitivity, Structure of Immune System, Immunodeficiency Disorders), Subject name: Microbiology
[{'content': 'Superantigen causes- \nSelect and explain. \nA. Polyclonal activation of T-cells, B. Stimulation of B cells, C. Enhancement of phagocytosis, D. Activation of complement', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 1.Superantigensare a class of molecules that can interact with APCs and T lymphocytes in a nonspecific way(attach to TCR by the side not in tne centre) . The superantigens act differently by interacting with MHC class II molecules of the APC and the Vb domain of the T-lymphocyte receptor. This interaction results in the polyclonal activation of a larger number of T cells (10%) than conventional antigens (1%), leading to massive cytokine expression and immunomodulation. fig:-Mechanism of action of superantigen 2. Examples: Staphylococcal toxin: TSST, Exfoliative toxin, Enterotoxins, Streptococcal toxin: Streptococcal pyrogenic exotoxin (SPE)-A Viral: EBV, CMV, Rabies nucleocapsid, HIV encoded nef (negative regulatory factor) Fungal superantigen: Malassezia furfur', 'role': 'assistant'}]