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 t reated, or not, with sunscreens with increasing sun protection factors (SPF 4, 8, 15 and 30), or their respective vehicles. Explants mere submitted, o r not, to increasing doses of UVB irradiation (312 nm), After an 18-h incub ation at 37 degrees C, epidermal cells were recovered through trypsinizatio n 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 asse ssed by the D50% in the absence of any topical treatment (mean 1615 +/- 839 J/m(2) from 14 experiments with values ranging from 500 to 3200 J/m(2)). F or all the tested sunscreens, the D50% values were significantly higher tha n those obtained without sunscreens or with their respective vehicles (P < 0.01), thus demonstrating their immunoprotective effect. IPFs were determin ed as the ratio of the D50% in the presence of sunscreen to that with vehic le alone. Although they displayed important individual variations, IPFs ran ked according to the sunscreen SPFs.