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Patients with systemic lupus erythematosus often possess antibodies against two nuclear antigens called Sm and RNP (ribonucleoprotein). We have established the molecular identity of these antigens by analyzing immune precipitates of nuclear extracts from mouse Ehrlich ascites cells labeled with 32P and 35S. Anti-Sm serum selectively precipitates six small nuclear RNA molecules (snRNAs); anti-RNP serum reacts with only two of these; and a third serum, characterized as mostly anti-RNP, precipitates a subset of three snRNA bands. Three of the six RNAs are identified by fingerprint analysis as the previously characterized and highly abundant nucleoplasmic snRNA species Ula (171 nucleotides), Ulb, and U2 (196 nucleotides). The other three RNAs (U4, U5, and U6) likewise are uridine rich and contain modified nucleotides, but they are smaller, with lengths of about 145, 120, and 95 residues, respectively. Each of the six snRNAs is complexed with and apparently antigenic by virtue of association with specific proteins. All three sera precipitate an identical complement of seven different polypeptides ranging in molecular weight from 12,000 to 35,000; these proteins are abundant in nuclear extracts, but are neither histones nor the major polypeptides comprising the 30S heterogeneous nuclear RNP particles of mammalian nuclei. Our data argue that each of the six snRNAs exists in a separate small nuclear ribonucleoprotein (snRNP) complex with a total molecular weight of about 175,000. We find that human antisera also precipitate snRNAs from a wide range of vertebrate species and from arthropods. We discuss the antigenic snRNPs in relation to the published literature on snRNAs and nuclear RNPs and consider possible functions of snRNPs in nuclear processes.Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown etiology (see refs. 1 and 2 for reviews). Antibodies to nuclear components, many of which have been identified as known macromolecules or macromolecular assemblies, are a hallmark of the disease. Antibodies directed against DNA, RNA, and nucleohistones are common. However, the molecular nature of two other antigens commonly precipitated by sera from patients with SLE, called ribonucleoprotein (RNP) and Sm, has remained obscure.Previous work on the RNP and Sm antigens has established that they are highly conserved nuclear components (3, 4). Immunodiffusion experiments using anti-RNP and anti-Sm sera have detected crossreacting material in a wide variety of mammalian tissues (3). Immunofluorescence studies (3, 4) have localized RNP entirely within the interphase nucleus, whereas Sm is reported to be largely, but not exclusively, nuclear. Most striking is the observation that the activity of RNP, as measured by immunodiffusion assays, can be destroyed by either RNase or trypsin (3-5). Sm is sensitive only to trypsin and is less heat labile, but appears antigenically related to RNP (3, 4, 6). Finally, velocity centrifugation and gel filtration studies (3, 4) have assigned a sedimentation constant of 7...

Mice of the strain MRL/Mp-lpr/lpr develop a lupus erythematosus-like syndrome that includes the production of autoantibodies specific for nucleic acid-containing cellular components. We have fused spleen cells from such a mouse with the myeloma SP 2/0 and examined the antibodies produced by the resultant cloned hybrid cell lines by using immunoprecipitation and immunofluorescence techniques. Three types of monoclonal antibodies, specific for Sm, DNA, or rRNA, all antigens to which patients who have lupus make antibodies, have been identified. Patient anti-Sm antibody had previously been reported to precipitate five small nuclear ribonucleoproteins that contain U-1, U-2, U-4, U-5, and U-6 RNAs. The monoclonal anti-Sm antibody gives the same immunoprecipitation pattern, providing direct evidence that the Sm antigen resides on all these RNA-protein complexes. Monoclonal anti-Sm antibody will be valuable in deciphering the biological function of these ubiquitous small nuclear RNPs. A simple competition radioimmunoassay using the monoclonal anti-Sm antibody to titer patient sera is also presented. Uses of monoclonal antibodies for the study of autoimmune disease are discussed.The sera of patients and mice that have autoimmune disorders contain antibodies whose presence often results in tissue injury. The mechanisms leading to the development of autoantibodies are not well understood. However, the appearance of specific antibodies in patient sera has been reported to be associated with particular clinical signs of disease (1). Studies with monoclonal antibodies having the same specificity as such autoantibodies could result in a clearer understanding ofboth the mechanisms leading to the formation of autoantibodies and the role of such antibodies in producing disease. Mouse monoclonal antibodies to DNA and ribosomal RNA have been described (2, 3).Autoantibodies also provide potent tools to probe the structure and function ofthe cellular constituents against which they are directed. We have previously used antibodies from the sera of patients who have systemic lupus erythematosus (SLE) to examine the antigens designated Sm, RNP, La, and Ro (4-6). Each of these antigens resides on discrete particles composed of RNA and protein and called either small nuclear ribonucleoproteins (snRNPs) or small cytoplasmic ribonucleoproteins.Anti-Sm has been found to precipitate five different snRNPs, containing the small RNAs U-1, U-2, U-4, U-5, and U-6, from mammalian cell extracts. One snRNP that bears the RNP as well as the Sm determinant appears to be involved in the nuclear splicing of mRNA precursors (7), while cellular roles for the Laand remaining Sm-bearing snRNPs and for the Ro-containing small cytoplasmic RNPs are unknown. The availability of monoclonal antibodies directed against snRNPs would eliminate many uncertainties in experimental interpretation raised by the use of patient sera.Antibodies to Sm are found in certain SLE patients (1), dogs with a lupus-like syndrome (8), and the MRL/Mp-lpr/lpr (MRL/1) and MRL/M...

Two small RNAs encoded by Epstein-Barr virus and complexed with protein are precipitated by antibodies from patients with systemic lupus erythematosus (Epstein-Barr virus-encoded RNA/La antigen/small nuclear ribonucleoprotein)

The RNP and Sm antigens recognized by lupus erythematosus antibodies are located on discrete particles containing single small nuclear RNA's complexed with proteins. The antigens Ro and La are also on ribonucleoproteins. The small RNA's in ribonucleoproteins with Ro are discrete, like those associated with RNP and Sm; in contrast, ribonucleoproteins with La contain a striking highly banded spectrum of small RNA's from uninfected cells as well as virus-associated RNA from adenovirus-infected cells.