Oral adjuvants enhance IgA responses to Streptococcus mutans

The induction of immune responses to orally-administered trinitrophenyl (TNP)-haptenated Streptococcus mutans or its cell wall components and enhancement of immune responses with oral adjuvants has been studied in high IgA responsive C3H/HeJ mice and in gnotobiotic rats. Gastric intubation of TNP-S. mutans to LPS non-responsive C3H/HeJ or syngeneic, LPS responsive C3H/HeN mice induced IgA responses as determined by measuring splenic plaque-forming cell (PFC) responses and IgA anti-TNP antibodies in serum, saliva, and urine. Higher IgA responses always occurred in C3H/HeJ mice given oral S. mutans antigen than similarly treated C3H/HeN animals. Oral administration of the adjuvants concanavalin A or S. mutans cell wall peptidoglycan (PG) with antigen resulted in augmented IgA responses, especially in C3H/HeJ mice. On the other hand, oral administration of muramyl dipeptide (MDP) with antigen boosted anti-TNP responses in C3H/HeN, but not in C3H/HeJ, mice. Gnotobiotic rats given S. mutans whole cells (WC) or purified cell walls (CW) by the oral route exhibited a salivary IgA immune response which was potentiated greater than twofold when antigen was given with PG or MDP. In other studies, S. mutans WC or CW antigen in water-oil-water (W/O/W) emulsion or liposomes was administered by gastric intubation to rats. Significant salivary IgA responses were induced with these antigen-adjuvant preparations. Although rats given S. mutans WC or CW were protected from S. mutans challenge, the greatest degree of caries immunity was obtained in animals which received antigen and adjuvant and which exhibited significant salivary IgA antibody levels. In preliminary studies, it was observed that local injection of rats in the salivary gland region with a ribosomal preparation from S. mutans resulted in a significant salivary IgA response and caries immunity. The potential for soluble and lipid carrier adjuvants in oral vaccines for induction of protective antibodies to S. mutans is discussed.