Interleukin production by human colostral cells after in vitro mitogen stimulation

The Role of Human Milk Immunomodulators in Protecting Against Viral Bronchiolitis and Development of Chronic Wheezing Illness

Infants who are breastfed are at an immunological advantage when compared with formula fed infants, evidenced by decreased incidence of infections and diminished propensity for long term conditions, including chronic wheeze and/or asthma. Exclusive breastfeeding reduces the duration of hospital admission, risk of respiratory failure and requirement for supplemental oxygen in infants hospitalised with bronchiolitis suggesting a potentially protective mechanism. This review examines the evidence and potential pathways for protection by immunomodulatory factors in human milk against the most common viral cause of bronchiolitis, respiratory syncytial virus (RSV), and subsequent recurrent wheeze in infants. Further investigations into the interplay between respiratory virus infections such as RSV and how they affect, and are affected by, human milk immunomodulators is necessary if we are to gain a true understanding of how breastfeeding protects many infants but not all against infections, and how this relates to long-term protection against conditions such as chronic wheezing illness or asthma.

Interleukin-2 in human milk: a potential modulator of lymphocyte development in the breastfed infant

Development of lymphocyte subpopulations and response to antigen exposure will be influenced by the limited ability of neonates to produce cytokines. In the case of cytokines such as interleukin (IL)-2 which are potent T lymphocyte regulators but poorly produced by newborn infants, the supply of cytokines through human milk could alleviate an immunological deficit and potentially aid the maturation of the immune system. We analysed human milk from 52 mothers (15-357 days postpartum) by ELISA to determine levels of aqueous IL-2, as well as production by human milk cells. IL-2 was detectable (>8 pg/mL) in the aqueous phase of 81% of all day 1 samples with no significant difference found in the mean concentration over 3 consecutive days. IL-2 was produced constitutively at detectable levels by 57% of milk cell samples and production was significantly increased by stimulation with Con A (380%). No correlation was found between aqueous and cellular IL-2, however there was a significant correlation between milk aqueous IL-2 and serum IL-2. This is the first report of IL-2 in the aqueous phase of human milk. A supply of exogenous IL-2 in human milk may provide the suckling infant with important immunological signals during a significant stage of T cell development.

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-1beta, interleukin-6, and tumor necrosis factor-a in the absence and presence of lipopolysaccharide was determined by enzyme-linked immunosorbent assay. Human milk cells spontaneously produced significantly less interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha 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-1beta, interleukin-6, and tumor necrosis factor-a in the mammary gland and have the capacity to respond to further stimulation after leaving the breast.

Selective compartmentalization of gammadelta-T lymphocytes in human breastmilk

In human breastmilk, T lymphocytes with gammadelta-receptor (TCR) are more frequent than those with alphabeta-TCR, in comparison with peripheral blood. Differential representation has also been demonstrated for subpopulations of gammadelta-T cells. Reactivity was visualized with three monoclonal antibodies against Vdelta1, Vdelta2 and Vgamma2 on T cells from the breastmilk and peripheral blood of 12 women who had recently given birth. Confirming the results with Vdelta1, it was found that Vdelta1 (p < 0.01) and Vgamma2 (p < 0.05) but not Vdelta2 were overrepresented on T cells in milk as compared with blood. This selective compartmentalization seems to reflect the homing of certain cells to the mammary gland.

Effect of human colostrum on interleukin-2 production and natural killer cell activity

The effect of human colostrum on the production of interleukin-2 (IL-2) and on natural killer (NK) cell activity by peripheral blood mononuclear cells (PBMC) was investigated in 50 healthy women. At concentrations as low as 0.5%, human colostrum stimulated IL-2 production; at a higher concentration (10%), IL-2 secretion was inhibited. A time and dose dependent inhibitory effect of colostrum on NK cytotoxicity was also observed. This inhibition could be reversed by the addition of human recombinant IL-2 (hrIL-2). The stimulation of IL-2 production induced by human colostrum might compensate for its inhibitory effect on NK cell activity. These findings suggest an additional mechanism by which breast feeding may affect the neonatal immune system.

Presentation of soluble and bacterial antigens by milk-derived cells to unprimed bovine T cells in vitro

The ability of cells isolated from bovine milk and peripheral blood to present soluble protein and particulate bacterial antigens to peripheral blood T lymphocytes was compared using a culture system which consistently supports antigen-specific, primary, proliferative responses. The present study shows that cells from blood and from milk can present antigen to unprimed T cells. Major histocompatibility complex class II restriction of the responses was demonstrated by abrogation of proliferation by the addition of anti-bovine class II monoclonal antibody to cultures. Although cells derived from blood or milk were shown to be capable of presenting antigen to T cells, differences in optimal culture conditions and kinetics of the resulting response were observed.

In vitro TNF, IL-6 and IL-2 production by rat milk cells following Trichinella spiralis infection

Trichinella spiralis-specific immunity can be transferred from immune mothers to suckling neonates via lactation, suggesting that milk from immune dams contains specific factors to T. spiralis. TNF and IL-6 are important cytokines in inflammatory processes, and IL-2 is essential in lymphocyte activation. Using cell line bioassays, we examined the capacity of rat milk mononuclear cells from immune and non-immune control dams to produce these cytokines following in vitro stimulation with mitogens or T. spiralis antigen. Milk cells were capable of producing IL-2, IL-6 and TNF upon Con A stimulation, and TNF and IL-6 upon LPS stimulation. The amount of these cytokines produced by mitogen-stimulated milk cells from T. spiralis-infected rats was similar to that produced by non-infected controls, although lower than that of corresponding blood mononuclear cells. Upon stimulation with T. spiralis antigen, milk cells from infected rats produced a significantly higher amount of TNF (158 +/- 39 U/10(6) cells) compared to non-infected controls (16 +/- 6 U/10(6) cells, P < 0.01), and also higher than that of the corresponding blood cells (60 +/- 10 U/10(6) cells, P < 0.01). Only small amounts of IL-6 and no IL-2 was secreted by milk cells from control or infected groups after stimulation with antigen. This study shows that rat milk cells are capable of synthesizing cytokines, and TNF produced by immune mothers may play a role in augmenting the neonate resistance to T. spiralis infection.