ANTIBASEMENT MEMBRANE AUTOANTIBODIES IN PATIENTS WITH ANTI-EPILIGRIN CICATRICIAL PEMPHIGOID BIND THE ALPHA-SUBUNIT OF LAMININ-5

Recent studies have identified a group of cicatricial pemphigoid patie nts who have IgG anti-basement membrane autoantibodies that recognize epiligrin, a set of disulfide-linked polypeptides closely related if n ot identical to laminin 5 (formerly called kalinin, nicein, or BM600). To further understand the pathophysiology of blister formation in the se patients, we have sought to identify the specific polypeptide(s) ta rgeted by their autoantibodies. Comparative studies show that sera fro m these patients (nine of nine), P1E1 monoclonal anti-epiligrin antibo dy, and polyclonal as well as monoclonal anti-laminin 5 antibodies imm unoprecipitate the same set of disulfide-linked polypeptides from medi a of biosynthetically radiolabeled human keratinocytes. Moreover, sera from eight of nine patients with anti-epiligrin cicatricial pemphigoi d immunoblot the alpha subunit of laminin 5 but show no reactivity to its beta or gamma subunits. In addition, circulating IgG from a repres entative patient was affinity-purified against the alpha subunit of la minin 5 and shown to bind the dermal side of 1 M NaCl split skin in th e same manner as autoantibodies from all patients with anti-epiligrin cicatricial pemphigoid. Sera from patients with bullous pemphigoid (n = 5), other forms of cicatricial pemphigoid (n = 5), epidermolysis bul losa acquisita (n = 4), or bullous systemic lupus erythematosus (n = 1 ) show no reactivity against any subunit of this laminin isoform in im munoprecipitation or immunoblot experiments. These findings correlate with prior reports showing that a monoclonal antibody directed against the alpha subunit of laminin 5 (i.e., laminin subunit alpha 3) induce s detachment of human keratinocytes from extracellular matrix in vitro as well as epidermis from human skin in situ. Together, these studies suggest that laminin subunit alpha 3 mediates attachment of basal ker atinocytes to epidermal basement membrane and that autoantibodies dire cted against it may be pathogenic.