Immune response in rats against lipopolysaccharides of Fusobacterium nucleatum and Bacteroides oralis administered in the root canal.

Lipopolysaccharides (LPS) prepared from one strain of Fusobacterium nucleatum and one strain of Bacteroides oralis were examined for immunological responses in rats. The LPS were applied to the pulp chamber of the two mandibular incisors. Using the plaque forming cell (PFC) method both antigens showed a rapid IgM response in the spleen, and a slower one in the submandibular lymph nodes. In comparison with the IgM response, the IgG response was somewhat slower and weaker for LPS of Bacteroides, while for LPS of Fusobacterium it was hardly detectable. After about 3 weeks both antigens gave a significant antibody titer in serum. The results showed that locally applied antigens of oral microorganisms can stimulate to an immune response both in the lymph nodes and the spleen resulting in circulating antibodies. The nature of this response is dependent on the chemical characteristics of the LPS-antigen.