Background: Recently, epidermal transglutaminase (TG) has been identified within the papillary IgA granules in dermatitis herpetiformis (DH). Although IgA type autoantibodies to tissue and epidermal TGs are characteristic serological markers for DH, these antibodies do not bind to normal papillary skin structures.
Aims: To test the possibility of IgA immune complex precipitation within the vessel walls as a first step in the pathogenesis of skin symptoms, we analysed immunoglobulin, complement, and epidermal TG deposition along the vascular system of DH skin.
Methods: Punch biopsy specimen were taken from 116 DH patients' skin, and evaluated for the presence of vascular immune precipitates by direct immunofluorescence. Skin samples from 16 DH patients were also studied for tissue and epidermal TGs.
Results: In 74 (64%) of the 116 DH skin studied, significant vascular staining accompanied the DH-specific granular IgA fluorescence (IgA and C3 in 39 patients; IgA alone in 18; IgA, C3 and IgM together in five; IgM alone in 12). In most cases (92%), the precipitates were detected in the small vessels of the papillary dermis; however, a subpapillary vascular fluorescence was also observed in a few patients (8%). Skin IgA colocalized with epidermal TG in the vessel walls and within the scattered papillary peri- and intervascular DH bodies. Tissue TG did not colocalize either with the immunoglobulins or with the complement precipitates of the dermis. Furthermore, we could not detect keratinocyte TG in the DH bodies nor in the vessel walls.
Conclusions: These findings support possible immune complex precipitation in the vessel walls of DH skin and further confirm the significance of epidermal but not tissue TG in the pathomechanism of skin symptoms.