Effect of Narrow Band Ultraviolet B on the Tissue Level of Interleukin 15 and Interleukin 15 Receptor Alpha Subunit in Active Non Segmental Vitiligo Cases.

Vitiligo is a T cell-mediated, autoimmune cutaneous disorder characterized by loss of functioning melanocytes from the basal layer of epidermis and/or hair follicles, leading to depigmented areas of the skin, mucous membranes, and/or hair (Strassner et al., 2018).

Multiple factors have been involved in disease development, with a prominent role of the immune system, in particular T cells. After repigmentation, vitiligo usually recurs in the same area, drawing attention to the fact that resident memory T cells (TRM) are present at the sites of vitiligo lesions. This was confirmed by a number of studies (Boniface et al., 2018 , Boniface& Seneschal., 2019 , Riding& Harris., 2019) showing that stable and active vitiligo perilesional skin is enriched with a population of CD8 TRM expressing both CD69 and CD103. CD8 TRM expressing CD103 are localized mainly in the epidermis. IL-15 is the only identified cytokine required for maintenance of CD8 TRM cells (Baumann et al., 2018 and Richmond et al., 2018).

Interleukin 15(IL-15) is one of Interleukin 2(IL-2) family members. It plays an important function in the pathogenesis of multiple cutaneous autoimmune diseases as psoriasis (Rückert et al.,2000) , alopecia areata (Ebrahim et al.,2019) and vitiligo (Atwa et al.,2020).

IL-15 receptor (IL-15R) is expressed on natural killer cells, dendritic cells, monocytes, fibroblasts, T cells and keratinocytes . IL-15R is composed of α (CD215), β (CD122), and γ (CD132) chains , The alpha chain occurs as both a soluble and a membrane-attached subunit (Vámosi et al., 2004 , Budagian et al., 2006 and Di Sabatino et al.,2011).

IL-15 stimulates neighbor cells by a trans-presentation mechanism through secretion of (IL-15. IL-15Rα complexes) from the surface of monocytes or dendritic cells into endosomes for its presentation in trans to neighboring cytotoxic cells or Natural killer cells ( Stonier & Schluns .,2010).