Accessory cell damage and loss of overall white cell viability inhibit lymphocyte responses after ultraviolet-B irradiation but without evidence of in vitro suppression.

The effect of different doses of ultraviolet B irradiation (UVR) on the proliferative responses of Balb/c spleen cells has been tested. In 72-hour cultures, there was dose-dependent suppression of proliferation in response to phytohemagglutinin (PHA). Cell viability after UVR was found to be reduced in a dose- and time-dependent manner. Proliferation increased by greater than 100 percent after low-dose (20 J/m2) UVR when either normal or gamma-irradiated peritoneal cells were added to the cultures, but not at higher doses. Delaying UVR until 24 hours after stimulation of cultures with PHA did not substantially increase [3H]-thymidine uptake. Stimulation of mixtures of UV-irradiated and control cells or incorporation of medium conditioned with UV-irradiated cells provided no evidence of suppression of proliferation. The accessory cell population is an important target for UVR, but cells are physically damaged to the extent that, at higher doses, the response to PHA stimulation cannot be restored.

Studies of allogeneic bone marrow and spleen cell transplantation in a murine model using ultraviolet-B light.

Ultraviolet irradiation inhibits alloreactive and mitogen-induced responses and might reduce both graft-versus-host and host-versus-graft reactions after bone marrow transplantation (BMT). We have studied proliferative responses to mitogens and reactivity in mixed lymphocyte culture after irradiation with ultraviolet (UV)-B light using splenocytes from Balb/c (H-2d) and CBA (H-2k) mice. Response to mitogens and in MLC was strongly inhibited by 20 J/m2 and abolished at 50 J/m2. Clonogenic cell recovery (CFU-GM; CFU-S) after UV-B irradiation was also reduced. When bone marrow and spleen cells were transplanted from parent (Balb/c) animals into F1 hybrid (Balb/c X CBA) recipients, all animals died with features indicative of graft-versus-host disease (GVHD) in 34 days. If the grafts were first irradiated with 100 J/m2 of UV-B at a mean wavelength of 310 nm, then 76% survived to day 80 when they were killed and shown to have normal marrow cellularity. The remainder died in marrow aplasia or of GVHD. H-2 typing in a group of surviving recipients showed either donor hematopoiesis only (8 of 15), mixed allogeneic chimerism (5 of 15), or recipient type hematopoiesis (2 of 15). Higher doses (200 to 300 J/m2) were detrimental to survival with 88% of recipients dying in marrow aplasia. Syngeneic BMT in Balb/c mice showed slower hematopoietic reconstitution when the grafts were first irradiated with 100 J/m2. After BMT from Balb/c to CBA mice all recipients of unirradiated grafts died within 54 days. By contrast, after graft irradiation with 100 J/m2 survival of recipient animals to day 80 was 59%. If these grafts were treated with 50 J/m2 survival was only 26% with an increase in deaths due to GVHD. Hematopoiesis at day 80 in a group of survivors studied by Ig heavy chain allotyping indicated donor type hematopoiesis in 6 of 10 (50 J/m2) and 2 of 9 (100 J/m2). These data indicate that UV-B irradiation inhibits lymphocyte reactivity and can prevent GVHD. However, there is clear in vitro and in vivo evidence of stem cell damage, such that autologous marrow recovery was demonstrated in a proportion of recipients. In parent----F1 UV-irradiated transplants, sustained hematopoietic recovery was effected in the majority by donor stem cells.

Immunomodulation by ultraviolet light: clinical studies and biological effects.

The interest of immunologists in ultraviolet (UV) irradiation stems from observations made in vitro and in vivo. In vitro, UV irradiation inhibits mitogen and mixed lymphocyte culture (MLC) responses and in vivo, it can induce cutaneous anergy, apparently via suppressor cells and serum factors. At present much interest is focused on the possible use of UV irradiation to permit transfusion without allosensitization and transplantation without either rejection or graft-versus-host disease (GVHD). Here, Derwood Pamphilon and colleagues discuss the current uses and potential of UV irradiation in transfusion and transplantation and relate these to experimental evidence on its effects at the cellular level.