5.7 Intestinal Mic roflora and Oral Tolerance
Animal studies comparing germ-free and conventional mice provide further evidence
for the importance of the intestinal microflora in the development of oral tolerance.
In such experiments, oral feeding of an antigen before immunization with
it can induce oral tolerance with the exact outcome depending on the nature and
dose of the antigen, the dosing schedule, and the age and genetic background of the
animals.99 IgG unresponsiveness to ovalbumin (OVA) lasted longer in conventional
C3H mice than in germfree animals of the same strain, when both groups were fed
20 mg OVA, then immunized three times intraperitoneally (i.p.) with 10 μg OVA
absorbed by alum.100 No significant differences were observed in the duration of the
IgE antibody response.