Litters fed from Rag -/- mothers, who have very few circulating or milk lymphocytes, made lower levels of antibody when compared with those fed from Rag +/+ mothers. Those with Rag +/- mothers showed similar responses to Rag +/+ pups. By exchanging mothers, the antibody responses in the pups could be altered. This observation suggests that milk lymphocytes are indeed a significant component to the neonatal murine immune system. It is not clear whether it is the lymphocytes themselves, or factors they produce, which are necessary, or at which cellular or molecular level the mechanism operates for this adjuvant-like activity. The observation may well link with that made in babies who have been shown to have significantly larger thymus glands if breast-fed.

The Rag mouse model allows other questions to be asked of milk production, the development of mastitis, and therefore milk quality and quantity. Such questions are important in agricultural situations where inflammatory changes are well known to reduce the milk output of domesticated animals. The term 'Rag' is relevant here, not as an eponym for 'Rapid activating gene' but as part of a name, 'Round Oak Rag Apple Elevation', a Holstein cow, had triplets, 26 sisters and 4215 three quarter sisters as a consequence of assisted reproductive technology (VanRaden (1997) J Dairy Sci 75). The lactation records of all these animals have been followed for three generations. This extensive database is beginning to allow careful genetic analysis of milk immunology; it too demonstrates the significance of maternal genetic factors to milk quality and the outcome of the calf consuming that milk.

Such data give a prospect to augmenting existing milks. Might milks be adjusted for the premature so as to enhance antibody responses in those whose trans-placental antibody levels are low? Might these factors allow improvement of the routine vaccination programmes, designed around the poor antibody responses of the infant human? Such prospects offer advantages to those working locally in neonatal nurseries or on a wider scale in public health.