title: Seasonal influences on immunological parameters in HIV-infected homosexual men: searching for the immunomodulating effects of sunlight.
abstract: In view of the capacity of ultraviolet radiation (UVR) to induce suppression of various immunological parameters and to enhance the viral replication of HIV, we investigated whether seasonal influences on immunological parameters that are relevant for HIV infection could be identified. As the sunny season is associated with high levels of ambient UVR, a decline of immunological parameters and an increase of the HIV viral load during the summer months might ensue. We analysed the immunological data of the HIV-infected homosexual men who participated in the Amsterdam Cohort Study on HIV infection and AIDS (1984-1996; n = 556). The effect of season on the individual development of various immunological parameters in time was examined by means of a random effects model for repeated measurements. Lower levels in the mean number of CD4+ T cells and the mean CD4+/CD8+ ratio were found during summer and spring, respectively (P = 0.0001/0.0001). For the CD8+ T cells, high mean values were observed both in April and September (P = 0.0001). The highest T-cell reactivity values were found during the summer (P = 0.0001). No effect of season on the viral load was established. The seasonal effect on CD4+ T cells seemed to be more pronounced at a more advanced stage of the HIV infection. It is concluded that the lower CD4+ T-cell counts during summer support the notion that solar UVR may have a suppressive effect on the cellular immunity of HIV-infected persons. However, whether this observation can be attributed to the effect of ambient UVR solely is questionable, as the other immunological parameters follow different seasonal courses and other reports suggest that both internal and environmental factors influence immunological parameters.
authors.affiliation: National Institute of Public Health and the Environment (RIVM), Laboratory for Pathology and Immunobiology, P.O. Box 1, 3720 BA Bilthoven, The Netherlands.
authors.forename: Fabian
authors.initials: F
authors.lastname: Termorshuizen
authors.forename: Ronald B
authors.initials: RB
authors.lastname: Geskus
authors.forename: Marijke T
authors.initials: MT
authors.lastname: Roos
authors.forename: Roel A
authors.initials: RA
authors.lastname: Coutinho
authors.forename: Henk
authors.initials: H
authors.lastname: Van Loveren
mesh_terms: D000328:Adult; D015496:CD4-Positive T-Lymphocytes / Q000528:radiation effects*; D015331:Cohort Studies; D004781:Environmental Exposure / Q000009:adverse effects; D015658:HIV Infections / Q000276:immunology*; D018451:Homosexuality, Male; D006801:Humans; D008297:Male; D009426:Netherlands; D012621:Seasons; D013472:Sunlight / Q000009:adverse effects; D014466:Ultraviolet Rays / Q000009:adverse effects*; D019562:Viral Load