Detection of antinuclear ribonucleoprotein (nRNP) antibody producing cells in peripheral blood lymphocytes from patients with mixed connective tissue disease.

Antinuclear ribonucleoprotein (nRNP) antibody forming cells were detected in pokeweed mitogen activated peripheral blood lymphocytes (PBL) from 5 of 6 patients with mixed connective tissue disease (MCTD) in the presence of rabbit antihuman IgG antiserum and guinea pig complement as hemolytic plaque forming cells (indirect PFC). In the absence of rabbit antihuman IgG antiserum, direct PFC were detected only in a case of PBL from the 6 patients. Although we have successfully detected mainly IgG anti-nRNP antibody forming cells in PBL from patients with MCTD, numbers of PFC did not correlate with the serum levels of IgG anti-nRNP determined by the enzyme linked immunosorbent assay.