Cell-mediated and humoral immune responses of guinea-pigs to the oral bacterium Actinomyces viscosus.

Actinomyces viscosus is a Gram-positive facultative rod indigenous to most human mouths. The guinea-pig was evaluated as a model for assessing cellular immune responses to a human strain of A. viscosus. Guinea-pigs, immunized with heat-killed A. viscosus cells or a water-soluble extract from A. viscosus (AVS), were tested for delayed-type hypersensitivity responses to A. viscosus 4 weeks after immunization. A week later, the guinea-pigs were terminated. Lymphocytes from peripheral blood, lymph node and spleen were tested for in-vitro blastogenic responses to heat-killed A. viscosus or the water-soluble extract. Plasma from these guinea-pigs were tested for the presence of precipitating antibodies. Positive in-vivo delayed-type hypersensitivity reactions and antibody responses to AVS occurred only in immunized guinea-pigs. A strong in-vitro blastogenic response to AVS or heat-killed A. viscosus occurred in lymphocytes from immunized guinea-pigs, but a weak response was detected in un-immunized animals. These data suggest that the guinea-pig can be used to evaluate different parameters of the immune response to oral bacteria such as A. viscosus.