This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunity, Subject name: Pathology
Type IV hypersensitivity reaction is mediated by which of following? 
Select and explain. 
A. B cells, B. Active T cells, C. NK cells, D. Plasma cells
B: Active T cells
Answer: B: Active T cells 
Explanation: Ans. b (Active T cells). (Ref. Textbook of Microbiology by Anantanarayan, 6th/l 55)HYPERSENSITIVITY REACTIONSHypersensitivity Reaction typePrototypeImmune MechanismsImmediate (type I)AllergiesAnaphylaxisBronchial asthmaCasoni's test (JK'09)Production of IgE antibodyAntibody mediated/ CYTOTOXIC (type II)Autoimmune hemolytic anemia; GBSProduction of IgG, IgM absImmune complex mediated (type III)Autoimmune diseases (SLE, RA, etc),Some bacterial, viral and parasitic infections (e.g. PSGN, Hepatitis B, malaria, etc), Disseminated malignancies,Serum sickness, Arthus reaction(Necrotizing vasculitis).Deposition of ag-ab complexes and complement activationCell-mediated (type IV)Contact dermatitisMultiple sclerosisType-1 DM,TB,Transplant rejectionActivated T-Lymphocytes Macrophage activation T-cell mediated cytotoxicity.Type VGrave's diseaseLATS