Enhancement of Murine Immune Responses to Orally Administered Haptenated Streptococcus mutans

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Abstract
The induction of immune responses to orally administered trinitrophenyl (TNP)‐haptenated Streptococcus mutans and its enhancement with muramyldipeptide (MDP), peplidoglycan (PG), and concanavalin A (Con A) were investigated in lipopolysaccharide (LPS)‐non‐responsive C3H/HeJ mice and the syngencic, UPS‐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 I week later, C3H/HeJ mice gave a significantly higher (P 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 μg or 500 μg/mouse) or purified PG (1 mg/mouse) at the time of TNp‐S. mutans immunization resulted in significantly (P≤ 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.