MODULATION OF IMMUNITY TO BORRELIA-BURGDORFERI BY ULTRAVIOLET-IRRADIATION - DIFFERENTIAL EFFECT ON TH1 AND TH2 IMMUNE-RESPONSES

Ultraviolet B (UVB) radiation suppresses the delayed-type hypersensiti vity (DTH) response to alloantigen by a mechanism involving interleuki n (IL)-10. It has been hypothesized, based on this result, that UV irr adiation shifts the immune response from a Th1 to a Th2 response. We t ested this hypothesis using Borrelia burgdorferi (Bb) as an antigen un der conditions where both DTH and antibody responses could be assessed . Mice were irradiated with a single dose of UV and then immunized wit h Bb in complete Freund's adjuvant (CFA). DTH was assessed by footpad challenge. At various time points thereafter, mice were bled, and the serum antibodies to Bb were quantitiated. Only IgG1, IgG2a, and IgG2b were produced in response to Bb. The IgG2a and IgG2b antibody response s, as well as the DTH response to Bb, showed UV dose-dependent reducti ons after UV irradiation. The primary IgG1 response to Bb was very low and was unaffected by UV irradiation; however, the IgG1 secondary res ponse was elevated in UV-irradiated mice. Injection of anti-IL-10 anti body into UV-irradiated mice within 24 h after UV exposure restored th e DTH response, as well as the IgG2a and IgG2b antibody responses. In addition, injecting recombinant murine IL-10 mimicked some of the effe cts of UV radiation. Our results support the hypothesis that in vivo, UV irradiation down-regulates Th1 immune responses, while leaving Th2 responses intact, and suggest that IL-10 is an important mediator of t his effect.