The immune system of newborn infants is immature with low activity of both innate and acquired immune reactions. Early nutrition has an impact on early immune responses. Dietary fatty acids are one nutritional factor noted to play a role in immune function. The omega-6 long-chain polyunsaturated fatty acid, ARA (Arachidonic acid) and the omega-3 fatty acid, DHA (docosahexaenoic acid) are found naturally in breastmilk and some infant formulas. The balance or relative amounts of ARA and DHA have been associated with immune response. Some commercial infant formula contains both ARA and DHA. However, the optimal balance of ARA and DHA has not been determined with respect to immune function. This study will assess two levels of ARA and the impact on immune response in healthy, term infants and whether genes that influence essential fatty acid metabolism alter the nutritional requirement of infants.

Inclusion criteria:

• healthy term infants
• birth weight, length and head circumference between the 5th and 95th percentile for gestational age (according to the National Center for Health Statistics growth charts)
• receiving >80% for their intake by mouth from commercial infant formula
• low-risk for allergy based on a negative family history.

Exclusion criteria:

• corticosteroid use
• red cell or plasma transfusions
• IV lipid emulsions prior to study entry
• major congenital malformations
• systemic or congenital infection
• significant neonatal morbidity
• maternal autoimmune disorders
• acute illness precluding oral feedings or conditions requiring feedings other than standard formula