Basophil recruitment and activation in inflammatory skin diseases

Background: Basophils are blood leukocytes constituting less than 1% of leukocytes. They share morphological and functional similarities with mast cells, but recent studies indicate that basophils play non-redundant roles via the release of several cytokines and lipid mediators, as well as functioning as antigen presenting cells. However, basophil infiltration into the tissues in human skin diseases remains to be addressed. Methods: The infiltration of basophils in 24 skin diseases (136 samples) was immunohistochemically analyzed using basophil-specific BB1 antibody. In addition, activation of blood basophils was examined by assessing CD203c expression with flow cytometry. Results: Basophils were detected in skin lesions of atopic dermatitis, prurigo, urticaria, bullous pemphigoid, drug eruptions, eosinophilic pustular folliculitis, insect bites, scabies, Henoch-Schonlein purpura and dermatomyositis. While cell densities in urticaria, bullous pemphigoid and eosinophilic pustular folliculitis were prominent, much lower numbers of basophils were seen in lesional skin of atopic dermatitis. Basophils were entirely absent in psoriasis vulgaris, mastocytosis, tumoral lesions, systemic sclerosis, and systemic lupus erythematosus. Levels of CD203c expression on blood basophils from prurigo and urticaria patients were higher than those from healthy donors. Conclusions: Basophils infiltrate into skin lesions more commonly than previously thought, and thus they may play important roles in a variety of inflammatory skin diseases.