Streptococcus sobrinus antigens that react to salivary antibodies induced by tonsillar application of formalin-killed S-sobrinus in rabbits

We previously found that tonsillar application of antigen induces a strong antibody response to Streptococcus sobrinus in saliva and blood plasma. Rab bits immunized against S. sobrinus by tonsillar application were highly res istant to experimental dental caries triggered by oral inoculation of livin g S, sobrinus organisms with sucrose. In the present study, we examined the reaction of S. sobrinus antigens to the antibodies induced by the tonsilla r application of S, sobrinus AHT-k in rabbits and compared them to those an tibodies induced by intramuscular injection. In an enzyme-linked immunosorb ent assay using ultrasonic fragments from mutans group streptococci, the sa liva and blood plasma selectively reacted to S, sobrinus AHT-k (serotype g) and serologically related streptococci (serotypes a, d, and h) in the sixt h week after tonsillar application, whereas the blood plasma in the sixth w eek after intramuscular injection reacted to the unrelated streptococci (se rotypes b, c, e, and f) in addition to the aforementioned streptococci. The antibody reactivity induced after tonsillar application was not lost after treatment of the antigen with heat or proteinase digestion, whereas these treatments resulted in a 70% decrease of the antibody reactivity induced by intramuscular injection. The inhibition by haptenic sugars and the decreas e in immunoreactivity by heat treatment and proteinase digestion suggested that 80% of the antibodies induced by tonsillar application reacted to sacc harides. These saccharide antigens appeared to be involved in a specific re action with S, sobrinus-specific streptococci and a selective reaction with serologically related streptococci, These antigens are probably involved i n anticaries reactions in experimental dental caries.