Effect of gestation length on the levels of five innate defence proteins in human milk

• The concentration of five host-defence proteins was measured in milk from 30 mothers
• Large variation was observed in all five proteins as well as total protein concentration
• The concentrations of the proteins decreased between weeks 2 and 5 of lactation in the Term and Premature birth groups, but not in the Very premature group
• The variability of these proteins may affect susceptibility to infection in the infant

BackgroundHuman milk contains a range of host defence proteins that appear to contribute to health and wellbeing, but their variability in abundance among individuals has not been very well characterised. Milk from mothers of premature infants has altered composition, but the effect of gestation length on the host-defence properties of milk is not known. A study was therefore undertaken to determine the variability and effect of gestation length on the abundance of five host-defence proteins in milk; lactoferrin, secretory IgA, IgG, secretory component, and complement C3.MethodsMilk was obtained from 30 mothers at their second and fifth week of lactation. These were from three groups of ten mothers having had very premature (V; 28–32 weeks gestation), premature (P; 33–36 weeks) or full term deliveries (T; 37–41 weeks). The concentration of each of the five proteins was measured in each milk sample by either ELISA or quantitative western blotting.ResultsThe concentration of IgG, and complement C3 ranged 22- and 17-fold respectively between mothers, while lactoferrin, secretory IgA, and secretory component ranged 7-, 9-, and 4-fold, respectively. The V group had significantly lower concentrations of four of the five proteins, the exception being IgG. Levels of these four proteins also decreased between weeks 2 and 5 of lactation in the P and T groups. Significant correlation was found between the concentrations of the host defence proteins within individual mothers, indicating some degree of co-ordinate regulation.ConclusionsMothers vary widely in the levels of host defence proteins in milk. Very short gestation length results in decreased abundance of host-defence proteins in milk. This may have functional implications for very premature infants.