Immunogenicity and protective capacity of Mycobacterium bovis BCG after oral or intragastric administration in mice.

After oral or intragastric administration of BCG to mice, comparable numbers of IFN gamma and TNF gamma producing cells were detected in both local (Peyer's patches) and central (spleen) lymphoid organs. Similar levels of precursors of CD8+ cytotoxic T lymphocytes specific for mycobacterial antigens were also found in the spleen and the mesenteric lymph nodes. These immune responses remained high over the course of 3 months, the duration of observation. Oral administration of BCG led to an enlargement of the cervical lymph nodes, which contained high levels of viable bacteria. In contrast, no adverse effects were observed in mice given the BCG via the intragastric route. These two routes of immunization induced similar levels of protective immunity to those observed in mice immunized via the subcutaneous route against a challenge with a virulent Mycobacterium tuberculosis strain (H37Rv).