Dermatitis herpetiformis is characterised by granular IgA precipitates in the 
papillary dermis. In contrast to other autoimmune blistering diseases, where 
tissue-deposited and circulating autoantibodies recognise the same target within 
the skin, in dermatitis herpetiformis a serum IgA reacting with a component of 
the healthy papillary dermis has not been detected. Recently, the antigenic 
specificity of pathognomic skin-bound IgA has been clarified: the immune 
precipitates contain epidermal transglutaminase, an enzyme not previously 
detected in the papillary region of normal skin. Furthermore, serum IgA in 
dermatitis herpetiformis has been found to bind epidermal transglutaminase. 
These findings may relate to the fact, that dermatitis herpetiformis is 
associated with gluten sensitive enteropathy, coeliac disease, which is 
characterised by IgA type autoantibodies to a closely related enzyme, tissue 
transglutaminase. The two transglutaminases are highly homologous, and 
therefore, cross reactivity of the two antibodies might explain why patients 
with gluten sensitive enteropathy, with or without skin disease, generally have 
serum autoantibodies to both enzymes. There is growing evidence that dermatitis 
herpetiformis should be considered as the skin manifestation of gluten 
sensitivity developing in those patients with mild coeliac disease, who produce 
epidermal transglutaminase autoantibodies of high avidity and affinity. Both the 
skin and the small bowel diseases are gluten dependent and are strongly 
associated with HLA DQ with no genetic differences to explain the two 
phenotypes. The question should be asked whether the rash in dermatitis 
herpetiformis is a classic autoimmune blistering disease or whether it has an 
immune complex basis, which is the most likely alternative.