IgA plasma cells in vascular tissue of patients with Kawasaki syndrome.

The etiology and pathogenesis of Kawasaki syndrome (KS) remain unknown. Clinical and epidemiologic features of KS are consistent with an infectious cause. To search for an etiologic agent of KS, a phage cDNA expression library was constructed from the aorto-iliac junction of a patient with fatal acute KS and screened with convalescent KS serum followed by anti-human Ig. Unexpectedly, 0.1% of the clones in the library react with anti-human Ig, indicating the presence of many Ig-producing B lymphocytes in the vasculitic tissue. To confirm this finding and to determine the isotypes produced, frozen vascular tissue sections from the patient and paraffin sections from coronary arteries from six additional patients with fatal acute or subacute KS were incubated with Abs to Ig isotypes. Histopathology of the tissues revealed the presence of many plasma cells in the inflammatory infiltrate. IgA was the predominant isotype produced in vascular tissue in all seven KS patients. IgM- and IgG-producing cells were less often detected. We conclude that there is a marked plasma cell response within the vasculitic tissue in KS, with unusual IgA production locally in this nonlymphoid, nonmucosal tissue. We suggest that the prominence of IgA plasma cells in the vascular infiltrate in the early, acute, and subacute stages of KS indicates an Ag-driven immune response to an etiologic agent with a respiratory or gastrointestinal portal of entry and speculate that this unusual immune response is integral to the pathogenesis of the illness.