Dimeric IgA in the rat is transferred from serum into bile but not into milk.

Intravenous administration of ductus thoracicus lymph with dimeric IgA antibodies against Escherichia coli 06 to lactating rat dams did not result in transfer of IgA antibodies into the milk, although the antibodies were detectable in serum 1 min after the administration and in bile 60 min later. After intravenous injection of serum from bile-duct-occluded (BDO) rats immunized in the Peyer's patches into lactating rat dams. IgA antibodies appeared in the serum and remained there up to 230 min. At this time no IgA antibodies were seen in the milk while they were present in bile. IgG and IgM 06 antibodies did not appear in bile or milk after intravenous administration of lymph or serum from BDO rats.