Effect of neonatal thymectomy on dental caries in rats

The effect of T-cell depletion on susceptibility to dental caries after infection with Streptococcus mutans was studied. Rats were neonatally thymectomized (Tx) and infected with S. mutans 6715 or locally immunized with the homologous organism before infection. The Tx rats uniformly exhibited a higher level of infection with S. mutans and subsequently showed a greater extent of carious activity. Correlation studies were performed comparing the level of salivary and serum anti-S. mutans antibodies and the relative amount of dental caries. The results demonstrated that salivary immunoglobulin A antibody after immunization and infection, or infection only, showed a significant negative correlation with dental caries. Also, after local immunization, serum immunoglobulin G antibody showed a negative correlation with dental caries in the rats. These findings further support a major protective role for salivary immunoglobulin A in experimental dental caries in rats.