Dual role of basophils in the pathogenesis of bullous pemphigoid elucidated by pathological and ultrastructural studies

Background Bullous pemphigoid (BP), one of the most common autoimmune blistering disorders, is characterized by early erythematous and bullous lesions. Histopathologically, eosinophilia in the dermal tissue is a common finding in BP. In addition, basophils infiltrate the BP skin lesion. Although basophils are involved in the induction of type 2 immunity along with eosinophils, their role in both the erythema and blister, as well as the chronology of their involvement, have not been investigated. Objectives To elucidate the role of basophils in BP development and resolution by performing early- and late-phase histopathological analysis of BP. Materials & Methods A total of 25 patients with BP who underwent biopsy for both erythema and bullous lesions and were not taking oral steroids at the time of biopsy, were selected. Biopsy specimens of the erythematous (inflammatory) and bullous (resolution) phases were compared by histopathology, immunohistochemistry and electron microscopy. Results During the early phase of BP, the number of basophils positively correlated with the number of eosinophils compared with other immune cells. In the late phase (bullous phase) of BP, the number of basophils significantly increased and more cell-cell contact between the basophils and M2 macrophages was noted, compared to the early phase Conclusions Basophils are involved in the development of BP and its resolution, in part, via cell-cell contact with eosinophils or M2 macrophages, as demonstrated by pathological analysis