Introduction: The idiotypic network in serum is critical to regulation of immune responses. It is not known whether a similar system is present in the common mucosal immune system. We therefore studied a well characterized receptor (Gb3, the natural receptor for shiga-like-toxins) and antibodies related to this neutral glycolipid in human milk.

Purpose: Our objective was to determine whether milk, as a surrogate marker of mucosal immune system function, contains idiotype/anti-idiotype secretory IgA (sIgA) and to relate secretory antibodies to serum antibodies.

Methods: Serum IgG and milk secretory IgA to anti-Gb3 (α-Gb3) and to anti-anti-Gb3(α-α-Gb3) were measured by EIA in 20 healthy women who had matched serum and milk samples collected 2-14 days post partum

Results: In milk sIgA α-Gb3 andα-α-Gb3 were present and their titers correlate (r=.651, P=.0019). In serum we detected both IgG α-Gb3 andα-α-Gb3 and the titers also correlate (r=.552, P=.0116). Nevertheless there was no correlation between the titers of serum and sIgAα-Gb3 (r=.0846, P=.723) or α-α-Gb3 (r=.1702, P=.4731).

Conclusions: An auto-antibody, idiotypic network is present in human milk. This network is independent of the serum network. We hypothesize that the human milk network is a way by which mothers confer passive protection and/or regulate the priming of the common mucosal immune system of their infants.