Ultraviolet-A (UVA-1) radiation suppresses immunoglobulin production of activated B lymphocytes in vitro

Abstract

Previous studies have shown that low-dose ultraviolet-A (UVA-1) total body irradiations were capable of improving disease activity in patients with systemic lupus erythematosus (SLE). We hypothesized that UVA-1-induced suppression of immunoglobulin production by activated B cells in the dermal capillaries could be (partly) responsible for this effect. Our experiments with donor skin demonstrated that approximately 40% of UVA-1 could penetrate through the epidermis. Irradiation of peripheral blood mononuclear cells (PBMCs) with 2 J/cm(2) of UVA-1 resulted in 20% cell death. This toxic effect could be prevented totally by preincubation of the cell cultures with catalase. This indicates that the generation of hydrogen peroxide plays a role in UVA-1 cytotoxicity. T cells and B cells appeared to be less susceptible to UVA-1 cytotoxicity than monocytes. With the use of a CD40-CD40L B cell activation method we measured immunoglobulin production after various doses of UVA-1 irradiation (0-2 J/cm(2)). The doses of 2 J/cm(2) caused a significant decrease of IgM, IgG, IgA and IgE production under the conditions of interleukin (IL)-10 or IL-4 (IgE) stimulation. Although UVA-1 can cause apoptosis of B lymphocytes, we show that relatively low doses of UVA-1 radiation also affect the function of these cells. Both effects may be responsible for the observed improvement of disease activity in SLE patients.

Fig 1

Mean penetration of three different irradiances of ultraviolet (UVA)-1 (23, 31 and 47 mW/cm²) through three different pieces of epidermis from normal Caucasian people (skin types II–III). The columns show means ± s.d.

Fig 2

The cytotoxic effect of ultraviolet (UVA)-1 on peripheral blood mononuclear cells (PBMCs), expressed as the mean percentage of dead PBMCs determined by trypan blue exclusion after a single irradiation with 0·5–10 J/cm² of UVA-1 radiation, in the presence and absence of catalase (20 units/ml). The values are shown as means ± s.d.

Fig 3

(a) Fluorescence activated cell sorter (FACS) analysis detecting B lymphocytes (CD20), T lymphocytes (CD3) and monocytes (CD14) of peripheral blood mononuclear cells (PBMCs) before and after the ultraviolet (UVA)-1 irradiation (10 J/cm²) [as used for the calculation of the data shown in (b)]. (b) The proportion of viable CD3 positive (T lymphocytes), CD14 positive (monocytes) and CD20 positive cells (B lymphocytes) 24 h after irradiation with 0, 0·5, 2 and 10 J/cm² UVA-1, determined by flow cytometric analysis. The values are presented as means ± s.d.

Fig 4

IgM production in non-irradiated cultures, after 2 weeks' incubation of CD40L positive fibroblasts and fibroblasts lacking CD40L, under interleukin (IL)-4- or IL-10-stimulated or non-stimulated culture conditions. Data are shown as means ± s.d.

Fig 5

The inhibitory effect of 0·5 or 2 J/cm² ultraviolet (UVA)-1 on IgM, IgG, IgA and IgE production in supernatants of peripheral blood mononuclear cells (PBMCs) cultures activated with CD40L and interleukin (IL)-10, during the second week of incubation. Data are expressed as means ± s.d. of the changes in the immunoglobulin production expressed in percentages.

Fig 6

The effect of added catalase on IgM, IgG and IgA production in supernatants of peripheral blood mononuclear cell (PBMC) cultures activated with CD40L and interleukin (IL)-10 after 2 J/cm² ultraviolet (UVA)-1 during the second week of incubation.