The threshold for immune cell reactivity to milk antigens decreases in cow's milk allergy with intestinal symptoms

Background: In cow's milk allergy (CMA) with intestinal symptoms, peripheral blood mononuclear cells (PBMCs) secrete tumor necrosis factor-alpha (TNF-alpha), altering intestinal function. However, the type of cow's milk protein (CMP) that triggers symptoms (intact or intestinally processed) is not known, and neither is the minimal amount required. Methods: PBMCs were isolated from infants with active CMA or cured infants just before a new challenge and stimulated with intact or intestinally processed CMP. Supernatants were tested for cytokine content and for their ability to perturb intestinal barrier capacity, measured in Ussing chambers in HT29-19A intestinal cells. Results: PBMCs from infants with active CMA secreted more TNF-alpha, when they were stimulated with intact rather than intestinally processed CMPs, and more TNF-alpha than PBMCs from cured infants. Accordingly, supernatants from PBMCs stimulated with intact but not intestinally processed CMPs significantly increased intestinal permeability. The CMP concentration required to trigger TNF-alpha secretion capable of altering intestinal function was very small in infants with active CMA (congruent to 2 mu g/ml), but about 300 times higher in cured infants. Conclusion: Intact rather than intestinally processed proteins stimulate PBMCs to release TNF-alpha and either intestinal barrier capacity. The threshold for PBMC reactivity of milk antigens drops considerably during active CMA with intestinal symptoms.