For a long time interferon (IFN) 4 was considered a specific antiviral protein, important in host defense against virus infections. In recent years it has become clear that IFN represent a heterogeneous family of proteins exerting pleiotropic biologic activities in addition to the antiviral action (1). Of special significance are the immunoregulatory activities associated with IFN (2), including stimulation or inhibition of antibody formation (3) and of various cellular immune reactions (4, 5). IFN is normally not demonstrable in the serum and other body fluids in the absence of an inducing stimulus, such as virus infection; however, IFN was found at high frequency in the sera of patients with autoimmune diseases including systemic lupus erythematosus (SLE), rheumatoid arthritis, and Sjogren's syndrome (6-8). In this report we describe the identification of antibodies to IFN-a (leukocyte IFN) present at a very high titer in the serum of an SLE patient.

Sera from six SLE patients and four other patients were first examined for the presence of IFN. A moderately high IFN titer was found in serum samples collected from one SLE patient on three different dates (Table I). The fact that this serum showed antiviral activity in assays in which both human and bovine indicator cells were used suggested the presence of IFN-a. Unlike IFN-/3 (fibroblast) or IFN-y (immune), human IFN-a is known to exert biologic activity in cells from many unrelated animal species (1 2, 13). IFN activity was not demonstrable in sera from the other patients included in this series. The presence of IFN-a in the serum of patient 1 was confirmed in a neutralization assay using specific antisera to human IFN-a,-p, and-y (Table 11). Antiviral activity was abolished after the addition of antibody to IFN-a, but not with the other two sera. Hooks et a/.(7) originally concluded that the IFN present in the serum of patients with SLE and other autoimmune diseases was IFN-y. A recent analysis of a large number of IFN-containing sera from SLE patients by Preble et a/.(€ 9, however, clearly showed that the IFN present had antigenic and biologic characteristics of human IFN-a. Our finding is consistent with the conclusion by Preble et a/. that only IFN-a is demonstrable