Objectives:  The  immunological  aspects of inflammatory  acne  are  still incompletely understood, so  this  study  aimed  to  investigate the  possible  role  of  IL‐17 and  25 hydroxycholecalciferol (25(OH)D3) in the  disease  pathogenesis and progression. Materials   and   Methods:  Across‐sectional   study   has   been    conducted  on   135 patients with  active  acne  vulgaris of various  severities and  150  matched controls. ELISA assays  of serum  and tissue  levels of IL‐17 and 25(OH)D3, also immunohisto- chemical and Western blotting  demonstration of the  expression patterns of lesional IL‐17 in comparison with control  group, were  performed.

Results:  The   mean   serum   levels   of   IL‐17   were   544.2  pg/mL ± 477.4   SD  and 42.2  pg/mL ± 8.1  SD for acne  patients and  controls,  respectively, with  significantly higher  levels among  the  patient group  (P < 0.05). Higher  IL‐17 expression levels in active  acne  lesions  when  compared with  its  level  in healthy  skin of  the  controls. The  mean  serum  levels  of  25(OH)D3  among  patients and  controls  were  33.3  ng/ mL ± 9.7  SD and  51.7  ng/mL ± 2.7  SD, respectively, with  significantly  lower  levels among  the  patient group  (P < 0.05). There  were  significantly  negative  correlations between IL‐17 and 25(OH)D3  levels (P < 0.001  for both).

Conclusions:  Deficiency  of vitamin D3 accompanied with higher IL‐17 in an inverse

pattern may have a possible  role in active  acne  vulgaris.