Enhancement of murine immune responses to orally administered haptenated Streptococcus mutans

The induction of immune responses to orally administered trinitrophenyl (TNP)-haptenated Streptococcus mutans and its enhancement with muramyldipeptide (MDP), peptidoglycan (PG), and concanavalin A (Con A) were investigated in lipopolysaccharide (LPS)-non-responsive C3H/HeJ mice and the syngeneic, LPS-responsive C3H/HeN strain. Both mouse strains manifested similar immune responses, primarily of the IgM isotype, after a single gastric intubation (GI) with TNP-S. mutans. However, when groups of animals were first carrier-primed by GI with S. mutans for 2 consecutive days, followed by a single GI with TNP-S. mutans 1 week later, C3H/HeJ mice gave a significantly higher (P less than or equal to 0.01) splenic IgA anti-TNP plaque-forming cell (PFC) response than identically treated C3H/HeN mice. Furthermore, saliva, urine and serum from these C3H/HeJ mice possessed high levels of IgA anti-TNP antibodies as determined by the enzyme-linked immunosorbent assay, whereas C3H/HeN mice exhibited low antibody levels. Oral administration of Con A (either 250 micrograms or 500 micrograms/mouse) or purified PG (1 mg/mouse) at the time of TNP-S. mutans immunization resulted in significantly (P less than or equal to 0.01) enhanced splenic IgA anti-TNP PFC responses, especially in C3H/HeJ mice. On the other hand, MDP promoted IgA anti-TNP PFC responses in LPS-responsive C3H/HeN mice but did not augment responses in C3H/HeJ animals. A similar immune response pattern was seen when antibody levels were measured in serum, saliva, and urine of both mouse strains. These results demonstrate that haptenated S. mutans is a good antigen for the induction of high IgA responses in orally immunized C3H/HeJ mice and that this high response can be enhanced with the adjuvants Con A and PG. However, MDP is ineffective in C3H/HeJ mice but enhances IgA responses in normal LPS-responsive C3H/HeN animals.