Immune response to nucleic acid antigens and native DNA by human peripheral blood lymphocytes in vitro.

The immunogenicity of DNA fragments (either oligonucleotide (oligo) or total DNA digest) covalently linked to keyhole limpet hemocyanin (oligo-KLH or DNA-KLH) was tested with peripheral blood lymphocytes (PBL) from 63 systemic lupus erythematosus patients (SLE) in vitro. PBL from 10 normal individuals and 11 rheumatoid arthritis (RA) patients served as controls. Antibodies to three nucleic acid antigens (oligo, denatured DNA (d-DNA), and native DNA (n-DNA] were assayed in supernatants of cultured lymphoid cells by a sensitive solid-phase radioimmunoassay. More than 50% of SLE and RA patient lymphoid cells formed spontaneous antibodies to one or several nucleic acid antigens. In contrast, only two normals did. After in vitro challenge with oligo-KLH or DNA-KLH, cultured lymphocytes of more than 50% of SLE patients formed antibodies to one or several nucleic acid antigens. Similar results were obtained in PBL from RA patients. In SLE patients, the response to both antigens was either monospecific or polyspecific, but DNA-KLH appeared to raise a greater proportion of antibody to n-DNA than oligo-KLH. A greater proportion of patients with active disease responded in vitro compared with those with inactive disease. A mixture of oligo together with KLH was not immunogenic in vitro. Oligo-KLH or DNA-KLH did not raise antibody to an irrelevant antigen, ovalbumin. Of particular interest, PBL from seven of 10 normal subjects formed antibody to n-DNA after challenge in vitro with oligo-KLH. The data support the view that DNA fragments could be an important immunogen in SLE. Furthermore, this study provides an in vitro model to test the tolerogenicity of similar fragments of DNA linked to self carrier molecules such as gamma-globulin.