What type of hypersensitivity reaction involves T-cell-mediated immune responses (delayed-type hypersensitivity)?

Type IV (delayed-type) hypersensitivity is T-cell mediated and does not involve antibodies. It is called 'delayed' because the reaction peaks 48–72 hours after antigen exposure. Examples include contact dermatitis, tuberculin skin test reactions, graft rejection, and some drug reactions. Type I is IgE-mediated (anaphylaxis, atopy). Type II is antibody-mediated cytotoxicity (hemolytic anemia, pemphigus). Type III involves immune complex deposition (serum sickness, lupus nephritis). Dental relevance: latex allergy (Type IV), nickel/metal contact reactions, and certain oral lichenoid drug reactions are Type IV.