Exposure of a small area of the human body to light leads to a fast decrease in the elevated pro-inflammatory cytokine plasma content and to an increase in the the anti-inflammatory factor concentration, which may be an important mechanism of the anti-inflammatory effect of phototherapy. These changes result from transcutaneous photomodification of a small volume of blood and a fast transfer of the light-induced changes to the entire pool of circulating blood.

The increase in skin microcirculation produced by pVIS light at the local and systemic levels is due to activation of NO synthesis in the irradiated area.

The immunological effects of visible and infrared light from laser and non-laser sources have remained insufficiently studied, which has restricted the use of light in the treatment of diseases associated with immune system disorders. The present randomised, placebo-controlled double-blind trial was designed to study changes in the humoral immunity of a large group of volunteers after exposure of a small body area to polychromatic visible and infrared polarized (VIP) and non-polarized (VInP) light (400-3400 nm, 95% polarization, 40 mW cm(-2), 12 J cm(-2) and 400-3400 nm, no polarization, 38 mW cm(-2), 11.2 J cm(-2), respectively). Serum immunoglobulins (Ig) M, A, and G were determined turbidimetrically, and the immune complexes (ICs) by precipitation with 5% polyethylene glycol and subsequent spectrophotometric analysis. A single VIP irradiation induced an average rise in serum IgM levels of 13% (p < 0.05). By the end of the 10 day course, it has exceeded the baseline level by 26%, with an increase in IgA levels of 17 and 12% (p < 0.04) one week after the last session. In subjects with a high IC content, it decreased rapidly to the normal level. A single exposure of volunteers to VInP light rapidly produced changes similar to those observed on VIP irradiation, but with an increase in IgM 2.3 to 3 times lower, independent of the initial levels. On the other hand, VInP light exposure decreased the IC content more than VIP light.

Both types of irradiation stimulated microcirculation at the local and systemic levels through a mechanism of enhancement of endothelium-dependent and endothelium-independent vasodilation, in which nitric oxide plays a major role.

Immunosuppressive effects of the minor component of the terrestrial solar spectrum, UV radiation, have been substantiated over the past several years. This raises the question of what influence the dominant part of the solar spectrum--visible and IR light-would have on the human immune system. In the present randomized, placebo-controlled double-blind study a small area of the body surface of volunteers was irradiated with polychromatic light (480-3400 nm), simulating the significant part of the terrestial sunlight irradiance spectrum and its power density. An average 2.5-fold to three-fold increase in spontaneous and phytohemagglutinin-induced DNA synthesis in peripheral blood lymphocytes (Lym) was revealed at 0.5-24 h after irradiation at a therapeutic dose (12 J/cm(2)) in subjects with low preirradiation levels of both processes. The in vivo findings were echoed in parallel in vitro experiments, when blood drawn from the same subjects was directly irradiated (2.4 J/cm(2)), or when the irradiated blood was mixed 1:10 with nonirradiated autologous blood to model events in the circulation following transcutaneous blood photomodification. Our data suggest that exposure of the human body to polychromatic visible + IR light may photomodify blood in the dermal vasculature of the irradiated area to lead to an immediate transfer of the light-induced effects to Lym of the entire circulating blood, which can result in modulation of Lym functional state at the systemic level.