Sera from 20 patients with antiepiligrin
cicatricial pemphigoid were studied to define the specific reactivity of their
IgG autoantibodies.
IgG from all patients bound exclusively to the dermal side of 1 mol/L NaCl split skin and immunoprecipitated
laminin 5 (alpha3beta3gamma2) from extracts of human keratinocytes (HKs). Immunoblot studies on purified
laminin 5 subunits demonstrated that patient
IgG bound alpha3 alone in 16 patients. In two patients,
IgG autoantibodies were directed predominantly to the gamma2 subunit, yet showed trace reactivity to alpha3 as well. Sera from two patients did not immunoblot any
laminin 5 subunits, their
IgG presumably immunoprecipitating
laminin 5 via a conformational
epitope. Sera from patients with alpha3 subunit-specific
IgG immunoprecipitated all subunits of
laminin 5 as well as
polypeptides of 190 and 200 kDa from the
conditioned media of HKs. Preclearance studies and experiments utilizing affinity-purified patient
IgG demonstrated that the latter signified
laminin 6 (alpha3beta1gamma1) that was bound by cross-reactive alpha3 subunit-specific patient
IgG. Sera from patients with gamma2 subunit-specific
IgG showed no reactivity to
laminin 6, except for faint reactivity provided by low levels of their alpha3 subunit-specific
IgG. Taken together, these findings indicate that antiepiligrin
cicatricial pemphigoid signifies an autoimmune response to subunits present in
laminin 5.