Dual-faceted regulation by butyrophilin 1A1 to produce MUC5AC and IL-8 from human colonic cell line HT29-MTX-E12.

Butyrophilin subfamily 1 member A1 (BTN1A1) is a major protein of the milk fat globule membrane, but its immunoregulatory function remains largely unresolved, despite its structural similarity to the B7 co-stimulatory molecules. In this study, we investigated the immunological significance of BTN1A1 in gastrointestinal epithelial cells. The human ectodomain of BTN1A1 expressed as a soluble Fc fusion protein (ectoBTN-Fc) was added to HT29-MTX-E12 cells as a model for gastrointestinal epithelial cells. In the absence of tumor necrosis factor (TNF)-α, it significantly promoted MUC5AC production via a weak activation of NF-κB signal transduction pathway. In contrast, prior incubation with ectoBTN-Fc inhibited TNF-α-provoked-IL-8 secretion by suppressing the phosphorylation of NF-κB p65. Binding analyses demonstrated that ectoBTN-Fc likely binds to HT29-MTX-E12 cells, followed by its endocytosis. These results suggest a dual-faceted regulatory function of BTN1A1. It reinforces intestinal mucosal barrier function under basal conditions, while it may endow a prophylactic effect alleviating strong inflammatory stimulation.