Immunofluorescence and immunoelectron microscopy analyses of a human monoclonal anti-epithelial cell surface antibody that recognizes a 185-kD polypeptide: a component of the paraneoplastic pemphigus antigen complex?

We recently reported the production of a human monoclonal antibody (MoAb) derived from a patient with pemphigus vulgaris (PV) that binds to the keratinocyte membrane and reacts with a 185-kD polypeptide by immunoblot analysis. We have since examined the tissue specificity of that MoAb, F12. By indirect immunofluorescence (IIF), F12 stained both the cell membrane and the basement membrane zone of stratified squamous epithelia. Moreover, MoAb F12 stained other epithelial tissues, such as urinary bladder, small bowel, thymus, and liver, and non-epithelial tissues, such as myocardium. Indirect immunoelectron microscopy (IIEM) analysis showed that MoAb F12 bound to a component common to desmosomal and hemidesmosomal plaques and to zona adherens-type junctions between hepatocytes and bile duct cells. Inhibition experiments were then performed with sera from patients with pemphigus vulgaris, pemphigus foliaceus, paraneoplastic pemphigus, or bullous pemphigoid. Three sera blocked F12 reactivity; two were from paraneoplastic pemphigus patients and the other was from the pemphigus vulgaris patient whose peripheral blood lymphocytes were used to make F12. All these sera recognized a 185-kD band that co-migrated with the polypeptide labeled by MoAb F12 on immunoblots. In addition, the IIF and IIEM staining patterns of MoAb F12 were similar to those observed with sera from two patients with paraneoplastic pemphigus. These observations suggest a relationship between MoAb F12 and the autoimmune response characterizing paraneoplastic pemphigus patients' sera.