<prompt> Hypersensitivity Pneumonitis is classically described as a:Type I hypersensitivity reactionTye II hypersensitivity reactionType III Immune complex HypersensitivityType IV Cell mediated Hypersensitivity  <response>: Answer is C Immune complex Hypersensitivity pneumonitis is an immunologically mediated response to an extrinsic antigen that involves both immune complex Type III and cell mediated Type IV hypersensitivity reactions. Classically however, Hypersensitivity pneumonitis was believed to be a immune complex Type III mediated hypersensitivity response which is therefore the better answer amongst the options provided. However in strict terminology both option C and D should be correct. Types of Hypersensitivity Reactions: Review Type I Hypersensitivity IgEQ Type II Hypersensitivity IgG IgMQ Cytotoxic, complement mediated lysisQ Includes.- Local: Eczema, Hay fever, Asthma Atopy.Q Systemic: Anaphylaxis. Examples based on type 1.11S Q: Includes: Complement mediated lysisY Antibody dependent cell mediated toxicity formerly classified as type Changes in cellular function former type V.Q - Increased function: Graves disease.Q - Decreased function: M. Gravis.e PhagocytosisY Examples includes: 1.Q Theoblad Smith phenomenon:Q This is anaphylaxis in guinea pigs. PK reaction Prusnitz Kunster:Q Demonstrate that IgE is homocytotropic i.e. species specific. Casonis test: Immediate type IgE H.S Those with Ag on RBC. - Blood transfusion reaction.Q - Hemolytic anemia e.g. with I.M. and mycoplasma.Q Those with Ag on Neutrophils: Agranulocytosis.Q Those with Ag on platelets: e.g. 1TP.Q Those with Ag on basement membrane: GoodpasturesQ Type III Immune complex IgM IgG Type IV Delayed hypersensitivity cellular immunity Includes: Local: Ahus reactionY Systemic: Serum sickness.Q Examples: Includes: Tuberculin test.Q Lepromin test.Q Contact dermatitis.Q Jones-Mote reaction cutaneous basophilic hypersensitivity.Q Graft rejection chronic.Q Shicks test.Q Post streptococcal G.N.Q Detected by RAJ1 Assay.Q Hyprsensitivity Pneumonitis is associated with both Type III and Type IV Hypersensitivity 