Chronic Low‐Dose UVA Irradiation Induces Local Suppression of Contact Hypersensitivity, Langerhans Cell Depletion and Suppressor Cell Activation in C3H/HeJ Mice

Abstract

It has previously been demonstrated that chronic low-dose solar-simulated UV radiation could induce both local and systemic immunosuppression as well as tolerance to a topically applied hapten. In this study, we have used a chronic low-dose UV-irradiation protocol to investigate the effects of UVA on the skin immune system of C3H/ HeJ mice. Irradiation with UVA + B significantly suppressed the local and systemic primary contact hypersensitivity (CHS) response to the hapten 2,4,6-trinitrochlorobenzene. Furthermore UVA + B reduced Langerhans cell (LC) and dendritic epidermal T cell (DETC) densities in chronically UV-irradiated mice. Ultraviolet A irradiation induced local, but not systemic, immunosuppression and reduced LC (32%) but not DETC from the epidermis compared to the shaved control animals. Treatment of mice with both UVA + B and UVA radiation also induced an impaired secondary CHS response, and this tolerance was transferable with spleen cells. These results suggest that depletion of LC, but not DETC, may be involved in UVA-induced local immunosuppression in our model, and that tolerance was induced in the presence of normal numbers of DETC. Hence exposure of C3H/HeJ mice 5 days per week for 4 weeks with UVA can induce local immunosuppression and tolerance.

Ultraviolet A Radiation (320–400 nm) Protects Hairless Mice from Immunosuppression Induced by Ultraviolet B Radiation (280–320 nm) or <i>Cis-</i>Urocanic Acid

“…In contrast, a recent study by Bestak and Halliday [5] has found that UVA irradiation, at a total dose of UVA equivalent to the dose we have used, but administered chronically in 20 exposures rather than as a single exposure, significantly suppressed the local, but not the systemic contact hypersensitivity reaction in haired mice. It is difficult to reconcile this opposite finding from our study, apart from noting the differences in mouse strain and irradiation regime.…”

“…However the immunological consequences of ultraviolet A (UVA) radiation (320-400 nm) exposure are currently less well-defined and more controversial. Experimentation in mice has produced evidence that UVA radiation has an immunosuppressive action [5], or conversely has no effect on the immune status [1,6,7]. In addition, recent evidence indicates that UVA irradiation induces the photoisomerisation of trans-urocanic acid in mouse and human skin [8][9][10], but that this reaction is not necessarily followed by immune suppression [8,9].…”

Wavelength dependency for UVA-induced suppression of recall immunity in humans

“…In the present study, UVAI but not UVAII also caused significant, dose-responsive immunosuppression in vivo in humans. Chronic low-dose UVA, similarly to UVB, reduces Langerhans cells from the epidermis of mice and results in activation of tolerance as shown by transfer of suppressor cells [21]. UVAII was previously found to cause immunosuppression in mice and humans, via mechanisms which appear similar to those following UVB exposure [22,23].…”

The role of antioxidants in photoprotection: A critical review

“…35,36 Mechanistic studies using sunscreens and AOxs specifically implicate ROS in UV-induced immunosuppression, measured by depletion of epidermal Langerhans cells (LC) and suppression of contact hypersensitivity in skin studies. 37 With the application of sunscreen, depletion of epidermal LC is prevented and delayed hypersensitivity is improved. The degree of protection is directly related to the level of UVA protection.…”