In vitro determination of sunscreen immune protection factors.

The present study was aimed at determining immune protection factors (IPFs) for sunscreens. Human skin explants from donors of phototype II-III were treated, or not, with sunscreens with increasing sun protection factors (SPF 4, 8, 15 and 30), or their respective vehicles. Explants were submitted, or not, to increasing doses of UVB irradiation (312 nm). After an 18-h incubation at 37 degrees C, epidermal cells were recovered through trypsinization and tested in a mixed epidermal cell/T lymphocyte reaction. The UVB dose providing 50% immunosuppression (D50%) was determined graphically. We first demonstrated a large difference in the individual response to UVB, as assessed by the D50% in the absence of any topical treatment (mean 1615+/-839 J/m2 from 14 experiments with values ranging from 500 to 3200 J/m2). For all the tested sunscreens, the D50% values were significantly higher than those obtained without sunscreens or with their respective vehicles (P < 0.01), thus demonstrating their immunoprotective effect. IPFs were determined as the ratio of the D50% in the presence of sunscreen to that with vehicle alone. Although they displayed important individual variations, IPFs ranked according to the sunscreen SPFs.