Antibody to nuclear ribonucleoprotein penetrates live human mononuclear cells through Fc receptors

Abstract

IT is commonly accepted that antibodies do not penetrate living cells. In only one study anti-purine and anti-nucleoside antibodies were found to penetrate fertilised sea urchin eggs and modify their development¹. Such penetration has been considered unusual and the addition of anti-DNA antibodies does not affect mammalian tissue cells in culture². Direct immunofluorescence of skin biopsies of patients with mixed connective tissue disease (MCTD) using fluorescent anti-IgG has occasionally shown speckled intranuclear fluorescence^3–5 but it is doubted that IgG entered the cells while still viable. Patients with MCTD have high titres of antibody to nuclear ribonucleoprotein (RNP)^6,7 which also gives a nuclear speckled pattern on cell substrates in direct immunofluorescence⁸. Should the antibodies to cellular components and nucleic acids which occur in autoimmune diseases be able to penetrate living cells, a novel mechanism of immunologically mediated damage and/or dysfunction could operate. We show here that anti-RNP IgG can penetrate viable human mononuclear cells (MNC), by their surface Fc receptor, and react with their nuclear RNP.