Exposure to Low Doses of Solar‐Simulated Radiation Induces an Increase in the Myeloid Subtype of Blood Dendritic Cells

Abstract

Exposure to ultraviolet radiation causes alterations of cutaneous and systemic immunity. The aim of our study was to assess the influence of low doses of solar-simulated radiation (SSR) on the phenotypes of blood dendritic cells (BDC). Healthy volunteers (94) were irradiated with a dose of 1.2 SED (standard erythema dose) of SSR for 2, 10 or 30 consecutive days. Blood samples were taken before the first exposure and 24 h after final exposure. The three main subsets of BDC were distinguished by flow cytometry: BDCA-2(+)/CD123(+)/HLA-DR(+) (plasmacytoid, PDC) and two myeloid subtypes BDCA-1(+)/CD11c(+)/HLA-DR(+) (MDC1) and BDCA-3(+)/CD32(-)/HLA-DR(+) (MDC2). The percentage of total DC was elevated in all groups by the UV exposure and was significantly increased after 2 and 30 days of irradiation (P = 0.006 and P = 0.018, respectively). A particularly distinct increase was observed in the percentage of the MDC1 after 2 and 30 days (P = 0.022 and P < 0.0001, respectively). The MDC2 showed an increase after 10 days and a subsequent significant decrease after 30 days of irradiation (P = 0.031). A significant increase in PDC was found after 2 days of irradiation (P = 0.0006). Exposure to SSR induced an increase in the percentage of BDC in healthy human individuals, especially apparent in the MDC1 subtype.