Incidence of serum antibodies to native type I and type II collagens in patients with inflammatory arthritis.

Using a new solid-phase double-antibody radioimmunoassay we have determined the incidence of serum IgG antibodies to native bovine type I and type II collagens in patients with rheumatoid arthritis (RA), ankylosing spondylitis (AS), and psoriatic arthritis. Raised serum IgG antibody levels to native type I collagen were present in 49% of patients with RA, 30% with AS, and none of the patients with psoriatic arthritis. Raised serum IgG antibody levels to native type II collagen were present in 42% of patients with RA, 30% with AS, and none of the patients with psoriatic arthritis. In rheumatoid arthritis there was a lack of correlation between IgG antibody levels to collagen and the erythrocyte sedimentation rate, IgG rheumatoid factor, and circulating immune complexes measured by the Clq-binding activity. In ankylosing spondylitis IgG antibody levels to native type II collagen were raised only in patients with peripheral joint involvement. The significance of IgG anticollagen antibodies is not certain, but parallels with rheumatoid factor are discussed.