Ultraviolet radiation reduces resistance to Mycobacterium tuberculosis infection in BCG-vaccinated guinea pigs

SummaryUltraviolet radiation (UVR) in sunlight suppresses anti-microbial immunity and may impair vaccine inefficacy. To investigate whether UVR reduces the protective efficacy of BCG vaccine, guinea pigs were exposed to a single dose of 5.6, 11.2, or 22.5 kJ/m2 of UVR either 3 days before or 3 or 28 days after BCG vaccination and then challenged by the aerosol route with virulent Mycobacterium tuberculosis 6 weeks later. Pre-challenge skin test responses to purified protein derivative (PPD) were significantly reduced in the UV-irradiated animals. Similarly, exposure to UVR reduced the proliferation of spleen cells to PPD, altered cytokine mRNA expression in spleen and lung digest cells, and increased the colony forming units (CFU) in the lungs of M. tuberculosis-infected guinea pigs at 5 weeks post-infection. Spleen IFN-γ, TNF-α, IL-10 and IL-12p40 mRNA levels were higher when exposed to 5.6 kJ/m2 UVR, while the levels were significantly reduced at 11.2 and 22.5 kJ/m2. Lung cell IL-10 mRNA expression increased at all UVR doses. Thus, UVR exposure a few days before or after BCG vaccination at a distant unirradiated site impaired vaccine-induced resistance against virulent M. tuberculosis in guinea pigs possibly by altering cytokine responses in a UVR dose-dependent manner.