Cytokine production by human milk cells and peripheral blood mononuclear cells from the same mothers

Samples of milk (n = 80) and venous blood were collected at 5 weeks postpartum from 82 lactating mothers. Human milk cells and peripheral blood mononuclear cells were isolated and the production of interleukin-1, interleukin-6, and tumor necrosis factor- in the absence and presence of lipopolysaccharide was determined by enzyme-linked immunosorbent assay. Human milk cells spontaneously produced significantly less interleukin-1, interleukin-6, and tumor necrosis factor- than peripheral blood mononuclear cells in the absence of stimulation. In vitro stimulation of human milk cells with lipopolysaccharide (500 ng/ml) for 24 hr increased cytokine production by approximately 40–50%, whereas peripheral blood mononuclear cells responded to lipopolysaccharide (200 ng/ml) with increased cytokine production of up to 350%. These observations suggest that cells in milk are capable of active involvement in the production of the interleukin-1, interleukin-6, and tumor necrosis factor- in the mammary gland and have the capacity to respond to further stimulation after leaving the breast.