Use of a synthetic peptidoglycan-precursor immunogen and its antibodies as a probe of infectious diseases in man.

Antibodies to a peptide sequence found in peptidoglycan (PG)- precursors (Lys-D-ala-D-Ala) have been found in man and their titers are elevated in several human diseases. Antibodies in rabbits were elicited by a synthetic immunogen containing these PG-precursor sequences, affinity purified with the precursor linked to Sepharose and shown to cross-react with bacterial by-products, such as the high molecular weight soluble peptidoglycan (SPG) from Staphylococcus aureus, which contain these sequences. SPG are secreted by some gram-positive bacteria when grown in the presence of penicillin. Serological studies have indicated that SPG may be the natural immunogen in man. The affinity purified antibodies cross-reactive with Lys-containing SPG plus vancomycin which has a similar specificity have been used to develop an ELISA capable of detecting as little as 50 pg/ml of SPG. Using this ELISA, about half of the human volunteers that took an oral 250 mg dose of penicillin V had detectable levels of SPG in their urine six hours later. There are structural differences among SPG which may be useful in identifying the bacteria responsible for the SPG. The SPG from Bacillus subtilis has diaminopimelic acid (A2pm) instead of lysine. Using the antibody to the synthetic immunogen, the A2pm-containing SPG gave a strong color reaction with the ELISA. However, the sensitivity was about an order of magnitude less than that for the Lys-containing SPG from S. aureus.