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The development of immunoglobulins IgG1, IgG2a, IgM and IgA was studied in germ-free BALB/c mice during the first 14 weeks of life. A transfer of maternal IgG1 and IgG2a was demonstrated during the first 2 weeks of this period. Endogenous synthesis of immunoglobulins was found only for IgM, the level of which was significantly higher at the end of the period than in a conventional group. After oral association of germ-free BALB/c mice with an intestinal hexaflora, the serum concentrations of IgG1, IgG2a and IgA increased. The levels of IgA, and of IgG1, were higher in the associated group than in the conventional group.
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Nielsen et al. (1980) studied this question.
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