Two groups of bullous pemphigoid antigens are identified by affinity-purified antibodies

Abstract

The bullous pemphigoid antigen was originally described as a 240-kD protein extracted from human epidermis, but a subsequent report has described patients' sera which react with epidermal proteins of molecular masses 240, 200, 180, 97, and 77 kD. We have evaluated the heterogeneity of the pemphigoid antigens identified by the sera of 10 patients with clinically typical bullous pemphigoid. We used indirect immunofluorescence and Western immunoblots of epidermal extracts prepared from epidermis separated by either 1 M salt or 20 mM EDTA to characterize the reactivity of both crude sera and affinity-purified antibodies. Affinity purification of antibodies was performed with either normal human epidermis or protein bands blotted onto nitrocellulose as immunoabsorbents. The anti-basement membrane antibody titers determined by indirect immunofluorescence on the saline- and EDTA-separated epidermis were identical. Despite this, Western blots of extracts prepared from EDTA-separated epidermis demonstrated greater amounts of the 240-kD antigen than saline split skin. Multiple antigens were recognized in epidermal extracts on Western blots by most crude BP sera, including bands at 240, 200, 160, and 100 kD. Different sera reacted with these antigens with a markedly different intensity, falling into two major groups, those bearing antibodies to the 240-200-kD antigens and those with antibodies to the 160-100-kD components. When epidermis was used as a substrate for affinity purification of bullous pemphigoid antibodies, the eluted antibodies reacted with multiple bands on Western blots, demonstrating the reactivity of anti-basement membrane zone antibodies with multiple proteins. Antibodies eluted from several individual bands of immunoblots were found to react with the basement membrane on indirect immunofluorescence. When these nitrocellulose-purified antibodies were reapplied to Western blots, they cross-reacted within two groups, the 240-200 kD antigens and the 160-100 kD antigens. We conclude that pemphigoid antigens are best demonstrated when EDTA-split skin is used for extraction and that different pemphigoid sera may contain antibodies to two separate groups of basement membrane zone antigens.