Human milk is a source of hormones, peptides, and cytokines which play important developmental and host defense roles. Infants that are exclusively breastfed have a reduced incidence of infection. The ability of the neonate to resist infection is limited by defects in phagocytic, humoral and cellular immunity. Some of these defects can be remedied, in part by G-CSF, a lineage specific cytokine that regulates neutrophil proliferation, differentiation, function, and survival. Since it seems likely that human milk contains G-CSF(Gilmore et al, Eur J Clin Nutrition, 1994), we hypothesized that 1) the concentration of G-CSF would vary in fore, mid, and hind milk during a single collection, 2) colostrum would contain more G-CSF than mature milk (milk collected >48 hrs after delivery), 3) the concentration of G-CSF would increase in milk obtained from women with intra-amniotic infection compared to those without, and 4) milk obtained from women who delivered prematurely would contain less G-CSF than milk obtained from women who delivered at term. Following ultracentrifugation, the aqueous layer was removed and G-CSF concentrations were determined by ELISA. Prior to analyzing the samples, validation of the assay was performed and included the evaluation of linearity, precision, accuracy, and percent recovery. We found that 1) the concentration of G-CSF in fore, mid, and hind milk samples (N=6) was similar, 2) at term, colostrum (N=5) contained 317±151pg/mL G-CSF(p<0.05, compared with mature milk), and preterm colostrum (N=8) contained 80±35pg/mL G-CSF (p<0.05, compared with mature milk), 3) in women with clinical evidence of intra-amniotic infection, concentrations of G-CSF were 407±65pg/mL(N=3)(p<0.05, compared to preterm or term mature milk), and 4) mature milk from women who delivered prematurely contained 27±16pg/mL G-CSF (N=13) and mature milk from women who delivered at term contained 31±21pg/mL G-CSF (N=2)(p=0.8). We conclude that the concentration of G-CSF; 1) does not differ between fore, mid, and hind milk obtained from a single collection, 2) is significantly greater in colostrum than in mature milk, 3) is significantly greater in term colostrum compared to preterm colostrum, 4) increases significantly in milk during maternal intra-amniotic infection, and 5) is similar in mature preterm and term milk. We speculate that G-CSF in human milk and colostrum may have a local or sytemic protective role in fetal host defense, but its exact function in milk remains to be defined.
