Ans. D. Dermatitis herpetiformisDermatitis herpetiformisa. Histopathology:Neutrophilic microabscesses at adjoining papillae intermingled with a few eosinophils, giving a multilocular appearance.b. Immunopathology:i. Perilesional noninvolved skin exhibits granular deposits of IgA in the dermal papillae. No circulating anti-BM antibodies are found. Anti endomysial, anti reticulin, and antigliadin antibodies have been identified in serum in 72%, 25%, and 45% of patients with DH respectively.ii. Anti endomysial ab are of IgA class only and are diagnostic of DH.c. Immunoelectron microscopy:i. IgA deposits in the skin are in the form of amorphous grains 0.1 micrometer in size called DH bodies, mostly in sub basal membrane region but also in the papillary dermis.ii. Recently tissue transglutaminase has been identified as the autoantigen of IgA antibodies in celiac disease. Circulating IgA autoantibodies. Of IgA ab in celiac disease.iii. Circulating IgA autoantibodies to tissue transglutaminase are detectable in DH as well and their levels reflect extent of changes of jejuna mucosa.iv. The ultrastructural site of blister formation in DH is the lamina lucida.