The immune system of the neonate is not up to par and is therefore supported by the mother with transplacental IgG for tissue defence and numerous milk components for defence of mucosal membranes. This addition to the host defence of the infant is not such a passive process as long assumed.

Effects of transplacental IgG antibodies from the mother on the antibody response of the offspring.

It was noted that Swedish newborns, also of antibody deficient mothers lacking IgA and/or IgM, had IgM and/or IgA antibodies to poliovirus, although these viruses do not exist in the country. The explanation might be that anti-idiotypic antibodies to poliovirus were regularly transferred via the placenta to the offspring, possibly stimulating to an antibody response via the immunological network. This agrees with the observation that monoclonal anti-antibodies given to newborn mice against bacterial or viral antigens stimulated to a protective antibody response. However, a low dose of the monoclonal stimulated, whereas a higher dose turned off the response. Most recently we have proceeded with these experiments and found that these effects initiated in a first generation is transferred to a second generation of rats. In those experiments we used an E. coli 06 K 13 strain transfected with the gene for ovalbumin together with monoclonal idiotypes and anti-idiotypes against 06, K 13 and ovelbumin given at an early age. We then noticed that a monoclonal to one of these antigens could affect the response to all of the three antigens either as an enhanced responsiveness or tolerance. These observations suggest that the immune status of the mother may be quite deeply involved in shaping the immune response of the offspring.

Effects of the maternal immune system on the offspring via milk.

It has been noted that breastfeeding does not only provide protection against infections during lactation, but it continues for years afterwards. Breastfeeding also results in better vaccine responses than non-breastfeeding at the serum, as well as the mucosal level. In addition, the breastfed infant seems to control its immune system better than the non-breastfed. Thus breastfeeding seems to decrease the risk of allergy and possibly of type 1 diabetes, coeliac disease, and Crohn's disease. Furthermore renal transplants from the mother to her offspring functions better than such a transplant from the father - if she has breastfed her offspring. This effect is supported by animal experiments. These active effects on the immune system of the infant by breastfeeding may partly be due to the presence of anti-idiotypic antibodies in mother's milk. In a mouse model it was possible to make neonates respond to an E coli K 13 capsular polysaccharide vaccine by giving the monoclonal anti-idiotype to K 13 to the mothers after delivery, so it only reached the offspring via the milk. At that age there is normally no response to polysaccharides. The milk cells are most certainly important as well. It has been demonstrated in various ways that milk cells are really taken up from the gut, especially by the President of this meeting and her co-workers. Thus there are possibilities for transfer of active immunological information from the mother to her breastfed offspring obviously with lasting effects. The effects on allergy by breastfeeding have been suggested to remain for up to 17 years of age and those so successfully receiving renal transplants from their mothers who had breastfed them were adults. Thus it seems that the mother can make her offspring use its immune system for better protection against infections, but possibly also keep it under better control decreasing the risk for development of allergic and autoimmune diseases.