Dermatitis herpetiformis (DH) is a pruritic papulovesicular skin disorder of unknown cause, characterized by granular IgA deposits in the dermis along the dermoepidermal junction. It is associated with gluten-sensitive enteropathy and increased IgA production by gut lymphoid tissue. We report four cases of immunologically documented DH studied by immunofluorescence technique. Monoclonal antibodies against the IgA subclasses IgA1 and IgA2 were used. IgA1 without IgA2 was found in the cutaneous deposits in each case. The IgA1 had both κ and λ light chains in approximately equal quantities. Because normal gut-associated lymphoid tissue produces 70% IgA1 and 30% IgA2, while circulating IgA is primarily IgA1, it could be concluded that the IgA in the skin of DH patients is not produced in the gut. However, the subclass restriction of the IgA produced by pathologic gut-associated lymphoid tissue is unknown. Alternatively, both IgA1 and IgA2 may be produced by the gut, but only IgA1 is involved in the production of cutaneous lesions.
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