Butyrophilin (BTN) is the major protein associated with fat droplets in the milk. It is a member of the immunoglobulin superfamily. It may have a cell surface receptor function. The human butyrophilin gene is localized in the major histocompatibility complex (MHC) class I region of 6p and may have arisen relatively recently in evolution by the shuffling of exons between 2 ancestral gene families[7]
Btn1a1 regulates the amount of lipids and size of droplets expressed in milk. When the gene is compromised in laboratory mice, approximately half the pups died within the first 20 days and the remainder were significantly under-weight.
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Butyrophilin has been presented as a potential antigen which may be similar enough to myelin oligodendrocyte glycoprotein (MOG) to spur the immune system to attack myelin in a process known as molecular or epitopic mimicry. This suggests that ingestion of butyrophilin in dairy products from cows and goats may be a potential trigger for multiple sclerosis. Independent studies by a group in Germany have reached similar conclusions.[9][10]
The German group have used heavy doses of butyrophilin on mice with an experimental model for multiple sclerosis called EAE. They have found that this strategy, called immune tolerance, reduces the effects of the disease.
^"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^Vernet C, Boretto J, Mattei MG, Takahashi M, Jack LJ, Mather IH, Rouquier S, Pontarotti P (Mar 1994). "Evolutionary study of multigenic families mapping close to the human MHC class I region". J Mol Evol. 37 (6): 600–12. doi:10.1007/bf00182746. PMID8114113. S2CID19054302.
^Tazi-Ahnini R, Henry J, Offer C, Bouissou-Bouchouata C, Mather IH, Pontarotti P (Jan 1998). "Cloning, localization, and structure of new members of the butyrophilin gene family in the juxta-telomeric region of the major histocompatibility complex". Immunogenetics. 47 (1): 55–63. doi:10.1007/s002510050326. PMID9382921. S2CID1873778.
Taylor MR, Peterson JA, Ceriani RL, Couto JR (1996). "Cloning and sequence analysis of human butyrophilin reveals a potential receptor function". Biochim. Biophys. Acta. 1306 (1): 1–4. doi:10.1016/0167-4781(19)60000-x. PMID8611614.
Cavaletto M, Giuffrida MG, Giunta C, et al. (1999). "Multiple forms of lactadherin (breast antigen BA46) and butyrophilin are secreted into human milk as major components of milk fat globule membrane". J. Dairy Res. 66 (2): 295–301. doi:10.1017/s0022029999003507. PMID10376248. S2CID29228427.
Rhodes DA, Stammers M, Malcherek G, et al. (2001). "The cluster of BTN genes in the extended major histocompatibility complex". Genomics. 71 (3): 351–62. doi:10.1006/geno.2000.6406. PMID11170752.
