Invariant natural killer T cells from children with versus without food allergy exhibit differential responsiveness to milk-derived sphingomyelin.

BACKGROUND: A key immunologic feature of food allergy (FA) is the presence of a T(h)2-type cytokine bias. Ligation of the invariant natural killer T cell (iNKT) T-cell receptor (TCR) by sphingolipids presented via the CD1d molecule leads to copious secretion of T(h)2-type cytokines. Major food allergens (eg, milk, egg) are the richest dietary source of sphingolipids (food-derived sphingolipids [food-SLs]). Nonetheless, the role of iNKTs in FA is unknown.
OBJECTIVE: To investigate the role of iNKTs in FA and to assess whether food-SL-CD1d complexes can engage the iNKT-TCR and induce iNKT functions.
METHODS: PBMCs from 15 children with cow's milk allergy (MA), 12 children tolerant to cow's milk but with allergy to egg, and 13 healthy controls were incubated with α-galactosylceramide (αGal), cow's milk-sphingomyelin, or hen's egg-ceramide. iNKTs were quantified, and their cytokine production and proliferation were assessed. Human CD1d tetramers loaded with milk-sphingomyelin or egg-ceramide were used to determine food-SL binding to the iNKT-TCR.
RESULTS: Milk-sphingomyelin, but not egg-ceramide, can engage the iNKT-TCR and induce iNKT proliferation and T(h)2-type cytokine secretion. Children with FA, especially those with MA, had significantly fewer peripheral blood iNKTs and their iNKTs exhibited a greater T(h)2 response to αGal and milk-sphingomyelin than iNKTs of healthy controls.
CONCLUSION: iNKTs from children with FA, especially those with MA, are reduced in number and exhibit a T(h)2 bias in response to αGal and milk-sphingomyelin. These data suggest a potential role for iNKTs in FA.