Association of increased CD4+ T-cell infiltration with increased IL-16 gene expression in atopic dermatitis

The mechanisms involved in the initiation and the maintenance of skin inflammation in atopic dermatitis (AD) are poorly understood. Previous studies have demonstrated increased numbers of infiltrating CD4+ T cells in acute lesions compared with normal control skin. IL-16 is a cytokine that has selective chemotactic activity for CD4+ cells.

We sought to examine whether IL-16 expression might be upregulated in acute versus chronic AD.

We investigated the expression of IL-16 mRNA in skin biopsy specimens from acute and chronic skin lesions, as well as from the uninvolved skin of patients with AD and normal skin. Cryostat sections from 4% paraformaldehyde-fixed skin biopsy specimens were processed for in situ hybridization by using cRNA coding for IL-16 mRNA. Numbers of infiltrating CD4+ and CD8+ cells were also determined by immunocytochemistry.

There were positive signals for IL-16 mRNA both in the basal layer of the epidermis and in the dermis of AD skin biopsy specimens from all subjects studied. The numbers of epidermal and dermal IL-16 mRNA+ cells were significantly increased in acute skin lesions compared with chronic (P <.01) and uninvolved (P <.001) skin lesions and compared with normal skin (P <.001). The number of CD4+ cells was significantly increased in acute skin lesions compared with chronic (P <.01) skin lesions and uninvolved skin (P <.01) and compared with normal skin (P <.01). Significant correlations were found between the numbers of CD4+ cells and the numbers of epidermal (r = 0.82, P <.001) and dermal (r = 0.71, P <.001) IL-16 mRNA+ cells.

The results demonstrate that upregulation of IL-16 mRNA expression in acute AD is associated with increased numbers of CD4+ cells, suggesting that IL-16 may play a role in the initiation of skin inflammation, presumably through recruitment of CD4+ cells.