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': "All of these are antigen presenting cells (APC's)except -a) T cellsb) B cellsc) Fibroblastsd) Dendritic cellse) Langerhans cells \nSelect and explain. \nA. ac, B. bc, C. ad, D. b", 'role': 'user'}, {'content': 'Answer: A \nExplanation: T cells cannot be activated by soluble antigens.\nTherefore, presentation of processed antigen by antigen presenting cells is required for activation of T cell.\nThe initial step in immune response (whether humoral or cellular) is phagocytosis of the antigen by antigen presenting cells.\nThese antigen presenting cells process and present the antigen to T cells.\nThese activated T cells then interact with B cells (in humoral immunity) or with other T cells (in cell mediated immune response)', 'role': 'assistant'}]