This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'A possible source of "second signal" to a B-cell bound by specific antigen include - \nSelect and explain. \nA. EB virus, B. Endotoxin, C. Antigen-specific T-cells, D. Plasma cells', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Role of T cell in antibody formation:\n\nAntigen with class II MHC on antigen presenting cells activates the CD4 helper T cells. CD4 helper T cells produce cytokines that stimulate B cells which have already exposed to similar antigen.\nThough antibody is produced by B cells (after differentiating into plasma cells), coordination of helper (CD 4) T cells is also necessary.\nIn antibody formation, T cells are involved earlier than B cells.\nAfter antigen exposure, antigen presenting cells present antigen to CD 4 helper T cells, which then secrete cytokines that induce differentiation of B cells ( which have already been exposed to the same antigen) to plasma cells.\nPlasma cells form an antibody against that specific antigen.', 'role': 'assistant'}]