Impaired production and lack of secretion of interleukin 1 by human breast milk macrophages.

Interleukin 1 (IL-1) production by human breast milk macrophages (HMMø) in response to bacterial lipopolysaccharides (LPS) was investigated in 49 healthy mothers and compared with that of blood monocytes (HMo). IL-1 activity in 24 h HMMø culture supernatants was in most cases below the assay detection limits and much smaller than that of stimulated HMo (72 +/- 17 u/ml). Intracellular IL-1 activity in response to LPS in HMMø raised from less than 2 +/- 1 u/ml to 19 +/- 12 u/ml and was similar to that found in stimulated HMo (16 +/- 4 u/ml). Neither the low IL-1 production by HMMø nor its release into supernatants could be increased by stimulating with higher LPS concentrations (40-400 micrograms/ml) or when longer culture times were assayed (24-72 h). Inhibiting the production of prostaglandins by adding indomethacin to HMMø cultures, caused no effect either on IL-1 production or on its secretion to supernatants. The presence of inhibitors for the IL-1 thymocyte proliferative assay, in supernatants from HMMø, was excluded by mixing experiments with a known amount of IL-1. Thus, we conclude that HMMø produce four or five times less IL-1 than HMo in response to LPS stimulus. Furthermore, HMMø are completely unable to release the IL-1 produced.