[Occurrence and importance of colostral leukocytes]

Leukocytes have been identified as a physiological component of colostrum in numerous animal species. In each of the examined species, they have been shown to occur in a typical amount exhibiting slight differences in the composition of leukocyte subpopulations. According to previous opinions, colostral leukocytes merely accidentally transfer from blood to milk or represent a sign of mastitis. In contrast to this, it is now considered to be current knowledge that special mechanisms exist enabling these leukocytes to actively transfer into colostrum. The presented review provides an overview of the recent literature and demonstrates the significance of colostral leucocytes. In analogy to the passage of maternal immunoglobulins, colostral leukocytes migration also leads to a transition of immunity. The cells are enterally absorbed and distributed throughout the neonatal organism. Colostral leukocytes are found to accumulate in certain tissues and organs without losing their immunologic function. Merely the leucocytes of the own mother are absorbed and these cells complement the newborns' immune system. As several studies have demonstrated, this is not solely due to the cells' mere immunological function but also a consequence of a regulatory effect on the neonatal immune system. Especially T-helper and further regulatory cell types transferred via colostrum may help the newborn in optimizing and maturing their immunological situation. Colostral treatment methods such as mixing, freezing, heating and acidifying modifications warrant re-evaluation taking the above aspects under consideration.