Background: The immune consequences of adding 20:4n-6 and 22:6n-3 fatty acids to preterm infant formula are not known.
Methods: The effect of feeding preterm infants (14-42 days of age) human milk (Human Milk group), infant formula (Formula group), or formula with added long-chain polyunsaturated fatty acids 20:4n-6 and 22:6n-3 (Formula + LCP group) on isolated peripheral blood lymphocytes (by flow cytometry) and lipid composition (by gas-liquid chromatography) was determined. Lymphocytes were stimulated in vitro with phytohemagglutinin to measure soluble interleukin (sIL)-2R and IL-10 production (by enzyme-linked immunosorbent assay).
Results: With age, the percentage of CD3+ CD4+ T cells and the percentage of CD20+ cells increased in the Human Milk and Formula + LCP groups (P < 0.05), but not in the unsupplemented Formula group. Compared with the Formula group, CD4+ cells from the Formula + LCP and Human Milk groups expressed more CD45R0 (antigen mature) and less CD45RA (antigen naive) at 42 days of age (P < 0.05). At 42 days, IL-10 production was lower (P < 0.05) in cells of the Formula group than in cells of the Human Milk group. Production of IL-10 by the cells of the Formula + LCP group was not different from that produced by the Human Milk group cells. An age-related decrease (P < 0.05) in sIL-2R production by Formula + LCP lymphocytes was observed, but sIL-2R production at 42 days in the Formula + LCP group did not differ significantly from that in the Human Milk group. Compared with Formula alone, adding LCP to formula resulted in a lower C18:2n-6 and higher C20:4n-6 content in lymphocyte phospholipids (P < 0.05).
Conclusions: Adding LCP to a preterm infant formula resulted in lymphocyte populations, phospholipid composition, cytokine production, and antigen maturity that are more consistent with that in human milk-fed infants. This may affect the ability of the infant to respond to immune challenges.