Advances in Alopecia Areata

Immune Privilege

Immune privilege occurs at defined tissue compartments (e.g., anterior chamber of the eye, testis, blood-brain barrier, placenta) and are essential for normal organ function¹

Immune privilege is established by complex mechanisms that suppress inflammation and promote immune tolerance²

Certain areas of the hair follicle are immune privileged sites:

Hair bulge, which contains hair follicle stem cells³
Hair bulb during the anagen phase only⁴

It is hypothesized that the purpose of immune privilege in the hair follicle is to prevent anagen- and/or melanogenesis-associated autoantigens from immune recognition by autoreactive CD8+ T cells¹

Functional studies suggest that CD8+ NKG2D+ T cells are the major effectors in alopecia areata pathogenesis5

Functional studies suggest that CD8+ NKG2D+ T cells are the major effectors in alopecia areata pathogenesis⁵

Hair follicles that lose their immune privilege during the anagen phase are targeted by CD8+ T and NKG2D+ cells6

Hair follicles that lose their immune privilege during the anagen phase are targeted by CD8+ T and NKG2D+ cells⁶

Loss of hair follicle immune privilege in the anagen hair bulb is accepted as a key attribute in alopecia areata pathogenesis4

Loss of hair follicle immune privilege in the anagen hair bulb is accepted as a key attribute in alopecia areata pathogenesis⁴

Related Resources

Chapter 2: Mechanism of Disease of Alopecia Areata

This video describes the mechanism of alopecia areata through the four distinct phases of the human hair cycle.

References

Paus R, Ito N, Takigawa M, Ito T. The hair follicle and immune privilege. Review J Investig Dermatol Symp Proc. 2003;8(2):188-194. doi:10.1046/j.1087-0024.2003.00807.x
Hong S, Van Kaer L. Immune privilege: keeping an eye on natural killer T cells. J Exp Med. 1999;190(9):1197-200. doi:10.1084/jem.190.9.1197
Azzawi S, Penzi LR, Senna MM. Immune privilege collapse and alopecia development: is stress a factor? Skin Appendage Disord. 2018;4(4):236-244. doi:10.1159/000485080
Paus R, Bulfone-Paus S, Bertolini M. Hair follicle immune privilege revisited: the key to alopecia areata management. J Investig Dermatol Symp Proc. 2018;19(1):S12-S17. doi:10.1016/j.jisp.2017.10.014
Pratt CH, King LE Jr, Messenger AG, Christiano AM, Sundberg JP. Alopecia areata. Nat Rev Dis Primers. 2017;3:17011. doi:10.1038/nrdp.2017.11
Paus R, Bertolini M. The role of hair follicle immune privilege collapse in alopecia areata: status and perspectives. J Investig Dermatol Symp Proc. 2013;16(1):S25–S27. doi:10.1038/jidsymp.2013.7

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