Evaluation of Serum Levels of Interlukin-15 and Interlukin-21 in Patients With Alopecia Areata

Alopecia areata (AA) is a type of non-cicatricial alopecia. The most common presentation of AA is localized patches of hair loss on the scalp. The extensive forms of AA presented as diffuse hair loss of the scalp (alopecia totalis) and diffuse hair loss through the entire body including the eyelashes and eyebrows (alopecia universalis).

AA affects approximately 2% of the general population. AA occurs at any age. The peak of incidence is higher in the second and third decades of life.

AA may be associated with several autoimmune diseases including thyroid diseases, lupus erythematosus, vitiligo, psoriasis, rheumatoid arthritis and inflammatory bowel disease. The frequency of the disease varies between geographically separate populations. These diseases associations suggest a relationship between AA and autoimmunity.

Human hair has an important cosmetic and communicational role. We may find significant psychological distress in persons with partial and complete hair loss. AA is associated with psychiatric morbidity especially anxiety and depression.

The pathogenesis of AA involves a complex interaction between genetic, environmental and immune factors. The histopathology of the disease differs according to the stage of the disease. In the acute stage of AA, there is a dense accumulation of lymphocytes (CD4 &CD8) around hair bulbs so called swarm of bees. In chronic stage, the inflammation may or may not resolve, but there is increase in number of catagen and, or telogen hair and pigmentary incontinence. In the recovery stage, there is minimal inflammation and increase in anagen hair.

T-helper17 cells are unique subset of T-helper cells which produce many interleukins (IL) e.g. IL-17A, IL-17F, IL-21, IL-22, IL-6 and tumor necrosis factor (TNF). The maturation of Th-17 needs the stimulation of naïve T cells by both TGF and IL-21. IL-21 is a cytokine that is produced mostly by activated CD4 T cells. It controls the differentiation and activity of T cells, B cells and NK cells. IL-21 could be a promising marker in the diagnosis of AA and also can be used as a marker of its activity.

IL-15 is a pleotropic cytokine that has multiple effects on different body cell types. It affects the function of cells of both innate and adaptive immune system. IL-15 is well known to promote lymphocytic development and suggested to play a role in some autoimmune diseases e.g. multiple sclerosis, rheumatoid arthritis, ulcerative colitis and celiac disease. IL-15 inhibits the well-known self-tolerance that mediated by activation - induced cell death, promotes maintenance of CD8+ memory T cells with induction of some cytokines which involved in autoimmune process e.g. TNF- and IL-1B. IL-15 is positively correlated with the number and the extent of AA so it could be a possible marker of AA severity.