Immunomodulation by non-absorbable antibiotics given by the intragastric route.

To test the role of bacterial fractions released from intestinal flora during immunomodulation by antimicrobial agents, BALB/c mice were treated with the non-absorbable antibiotics polymyxin B or teicoplanin by the intragastric route. The composition of faecal microbiota and the capacity of spleen cells to proliferate in response to B-cell and T-cell mitogens were assessed at several times during the treatment. Both antibiotics lowered the count of some bacteria of the intestinal flora and induced significant modifications in spleen cell ability to proliferate in response to mitogens. Thus, the active fractions released from intestinal bacteria during antibiotic treatments may be able to induce immunomodulating effects.