CONSERVATION OF SALIVARY GLYCOPROTEIN-INTERACTING AND HUMAN-IMMUNOGLOBULIN G-CROSS-REACTIVE DOMAINS OF ANTIGEN I II IN ORAL STREPTOCOCCI/

In this study we localized more precisely the salivary glycoprotein-in teracting and the human immunoglobulin G (hIgG)-cross-reacting domains on the SR molecule, an antigen I/II-related protein from S. mutans se rotype f, Mapping of the SR molecule with polypeptides expressed by su bclones covering the entire molecule and with synthetic peptides demon strates that the salivary glycoprotein-binding domain is located in th e N-terminal alanine-rich repeats of the SR molecule. In order to inve stigate the degree of conservation of both regions in various oral str eptococci, we tested the reactivity of 8 representative strains of the mutans group and 11 nonmutans oral Streptococcus strains (S, anginosu s, S, milleri, S. constellatus, S. intermedius, S. mitis, S. sanguis, S. gordonii, S. salivarius, and S. mitis strains) with antipeptide ant ibodies in a whole-cell enzyme linked immunosorbent assay together wit h colony hybridization analysis using DNA probes designed to map these two regions, All the mutans group strains except S. rattus and the 11 nonmutans streptococcal strains showed a high conservation of the C-t erminal part of the SR molecule, especially the hIgG-cross-reacting do main, and less homology for the N-terminal salivary glycoprotein-bindi ng region. Almost all of the sera from patients with rheumatic disease reacted strongly with SR from S. mutans serotype f, P1 from S. mutans serotype c, and four peptides located in the hIgG-cross-reacting regi on and not with peptides located at the C and N termini and in the pro line-rich repeats. These results confirm that epitopes located within this region are immunogenic in humans and could lead to the synthesis of natural anti-IgG antibodies.