Detection of Antibodies to Bacterial Cell Wall Peptidoglycan in Human Sera

Abstract

A radioimmunoassay has been developed for the measurement of antibodies to peptidoglycan in human sera including patients with rheumatic fever and juvenile rheumatoid arthritis. The assay is based on the percentage of binding of the hapten 125I-L-Ala-γ-D-Glu-L-Lys-D-Ala-D-Ala, the major peptide determinant of peptidoglycan. Because of differences in the avidity of the antibodies in different sera, the amount of antibody was expressed as pentapeptide hapten-binding capacity (pentapeptide-HBC in ng/ml of serum).Fourteen out of 105 normal blood donors had a pentapeptide-HBC value ≥ 75 ng/ml serum. Values in healthy children 5 to 18 years of age were ≤ 50 ng/ml. Sixty-eight percent of the individuals with rheumatic fever had values ≥ 75 ng/ml, an indication that streptococcal infections can stimulate an immune response to peptidoglycan. Thirty-five percent of the patients with juvenile rheumatoid arthritis had values ≥ 75 ng/ml. Such a finding points to a possible association between bacterial infections and juvenile rheumatoid arthritis.