Nuclear ribonucleoprotein immune complexes in pericardial fluid of a patient with mixed connective tissue disease

We performed immunopathologic studies of the pericarditis present in a patient with mixed connective tissue disease. A large number of nuclear RNP (nRNP) immune complexes (ICs) were found in the pericardial fluid, but not in the serum. The pericardial small vessels had no deposits of IgG. These results suggest that locally formed nRNP ICs were closely associated with the pathogenesis of pericarditis in this patient.