Immunohistochemical detection of human basophils in late-phase skin reactions

Background: Human basophils are difficult to detect with classic histochemical stains at sites of allergic inflammation. The 2D7+ anti-basophil monoclonal antibody was used to identify basophils in skin during the late-phase response to a cutaneous allergen challenge. Methods: The 2D7+ monoclonal antibody was used on protease-digested sections of skin biopsy specimens obtained 6 and 24 hours after an allergen or buffer challenge. The skin chamber technique was used to compare buffer- and allergen-challenged sites at 6 hours, and intradermal injection of allergen was used to compare allergen-challenged sites at 6 and 24 hours. Results: Dramatic increases in the numbers of 2D7+ cells and in tissue staining by 2D7+ were observed 6 hours after allergen challenge compared with buffer challenge. Histamine levels in skin chamber fluid varied with 2D7+ cell concentrations. By 24 hours, 2D7+ cells and tissue staining appeared to diminish but were still detectable in the allergen-challenged sites. Basophils localized primarily in and around blood vessels, whereas mast cells remained mostly in the superficial dermis. Mast cells were 2D7− in both the allergen- and buffer-challenged skin. Metachromatic staining of 2D7 basophils with toluidine blue was absent in these tissue sections. Conclusions: The 2D7 monoclonal antibody provides a more sensitive and precise marker than histochemical staining for human basophil involvement during the late-phase response to an allergen challenge. Basophil infiltration was observed at 6 hours only after allergen challenge and persisted at similar levels by 24 hours. (J Allergy Clin Immunol 1998;101:354-62.)