Butyrophilin is a major component of the milk fat globule membrane (MFGM), a lipid–protein layer that surrounds fat droplets in mammalian milk. Biochemically it is a glycoprotein and a member of the broader butyrophilin (BTN) protein family, which is conserved across species and structurally related to immune‑linked protein families. Historically identified during studies of milk composition and secretion, butyrophilin’s primary biological role is in the formation, stabilization, and secretion of milk fat globules. In the context of food immunology, fragments and peptides derived from butyrophilin can act as distinct dietary antigens; their recognition by antibodies helps separate milk fat–associated immune patterns from responses to casein, whey, or other dairy components.

Elevated antibody responses to butyrophilin suggest that the immune system has recognized peptides from this milk fat globule protein. Patterns of elevation can differ by isotype: mucosal IgA responses may point to gut‑associated immune activity, while IgG elevations reflect systemic antibody recognition. Higher signals should be interpreted alongside symptoms and other Food Zoomer markers to identify coherent dairy‑related patterns. Low or absent antibody responses indicate little measurable immune recognition of butyrophilin peptides. This may reflect tolerance, limited exposure to that specific dairy component, or that immune activity is directed at other food antigens. Always evaluate butyrophilin results in the context of the full panel and clinical information.

Butyrophilin is included in Food Zoomer because it represents a distinct milk fat globule peptide not captured by casein or whey markers. Measuring antibodies to butyrophilin helps providers detect immune activity specifically tied to milk fat–associated components, improving the panel’s ability to differentiate dairy reactivity patterns and refine individualized dietary planning.