True about protein A of staph aureus -

Protein A Cell wall component of S aureus strains Characterized among a group of adhesins called microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) Binds to Fc terminal of lgG (IgG 1, 2, & 4 but not IgG3) Prevents opsonophagocytosis by PMNs Anti complementary Chemotactic propeies Protein A forms the basis of co-agglutination reaction shown byStaphylococcus aureus. Protein A binds to Fc poion of IgG (except IgG3) The Fab terminal remains unoccupied . This poion has specific site for its specific antigen. Therefore when Protein A bearing staph aureus are coated with IgG antisera and mixed with the corresponding specific antigen - Agglutination occurs known as co-agglutination reaction. Mitogen Gram-negative bacteria produce endotoxin during infection Has Mitogenic effects on B lymphocytes that increase resistance to viral and bacterial infections. Measles causes immunosuppression, by decreasing eosinophils and lymphocytes (both B and T cells) and depression of their response to activation by mitogens. eg- T-cell mitogen