Differential Effects of Sunscreens on UVB-Induced Immunomodulation in Humans

Abstract

Ultraviolet radiation has been shown to suppress the (skin) immune system both in animal species and in humans. Whether sunscreens can prevent immunosuppression is a matter of debate. This study investigated the protective capacity of a commercial sunscreen lotion in humans. Part of the right arm of healthy volunteers was exposed to erythemagenic ultraviolet B doses of 160 mJ per cm2 for four consecutive days. Before irradiation, sunscreen was applied either directly onto the skin or onto a piece of quartz fixed to the skin (to avoid penetration of the sunscreen in the epidermis where it cannot block the photoisomerization of trans-urocanic acid in cis-urocanic acid in the stratum corneum). The control group was irradiated without prior application of sunscreen. Four h after the last irradiation, epidermal sheets were obtained by the suction-blister method from both arms and epidermal cells were used as stimulator cells in the mixed epidermal cell lymphocyte reaction. Responses directed to epidermal cells derived from irradiated skin were expressed as percentages of responses directed to epidermal cells derived from the nonirradiated left arm. The mixed epidermal cell lymphocyte reaction responses in the control group were found to be significantly increased (205%). This enhancement of the mixed epidermal cell lymphocyte reaction responses was associated with an influx of CD36+DR+ macrophages in the irradiated skin. Application of the sunscreen, either onto a piece of quartz or directly onto the skin, prevented the increase of the mixed epidermal cell lymphocyte reaction responses and the influx of CD36+DR+ cells. In an earlier study, volunteers were exposed three times weekly to suberythemagenic doses of ultraviolet B over 4 wk, resulting in mixed epidermal cell lymphocyte reaction responses that were decreased to 20%. The same sunscreen was not able to prevent this suppression. These contradicting results indicate that the protective effect of sunscreens with respect to ultraviolet-induced immunomodulation is critically dependent on the choice of ultraviolet treatment.

Protection against UV‐induced suppression of contact hypersensitivity responses by sunscreens in humans

“…Functional restoration of alloantigen presentation to T cells by epidermal cells from in vivo ‐UVA1 and UVB‐exposed skin occurred in each of several experiments to at least a partial level (Table 3) (23, 35, 36), except when UVB was chronically applied thrice‐weekly over 4 weeks (37, 38). Thus, chronic exposure may not be modeled well by acute exposure, UV dose escalation may exceed sunscreen capacities, or compliance issues may come into play.…”

“…With regard to LC numbers, most studies revealed an incomplete protection against UV‐induced LC depletion (19, 23, 39). In one study using UVB, UV‐induced infiltration of macrophages was reversed by sunscreen, as was their associated APC functional activity (Table 3) (37). In none of these studies was a dose range of UV administered to determine an IPF‐APC (Fxn or #) and none used SSR.…”

The effects of pajama fabrics' water absorption properties on the stratum corneum under mildly cold conditions

“…The main product of the histidine-to-urocanic acid pathway plays an important role in skin physiology by maintaining SC hydration and affecting ultraviolet protection. [16][17][18] The products of the phospholipid-to-free fatty acid pathway are free fatty acids, which not only influence the normal SC acidification, but also play an important role in the dual functions of SC integrity and cohesion. 9 Lipids in the SC are known to play a decisive role in maintaining the barrier function of the skin.…”

Sunscreens: Is an Ounce of Protection Worth the Hassle?

“…More than one million new cases of nonmelanoma skin cancer will be diagnosed in the United States this year. 9,10 The burning question of course is, do sunscreens prevent skin cancer? As sunlight has been implicated as the major environmental agent that causes skin cancer, we have sought ways to reduce the risk of developing skin cancer without compromising our love affair with the great outdoors.…”

“…8 Therefore it is important to recognize that sunscreens do not completely prevent UV-induced immunosuppression, and that the UV threshold for immunosuppression is lower than for erythema. 9,10 The burning question of course is, do sunscreens prevent skin cancer? There are data to support the notion that high-SPF sunscreens can reduce the risk of actinic keratoses 11,12 and squamous cell carcinomas.…”