title: Seasonal immune modulation in humans: observed patterns and potential environmental drivers.
abstract: BACKGROUND
  Cyclical fluctuations in host immunity have been proposed as a driver of respiratory infection seasonality, however few studies have attempted to directly assess whether or not seasonal immune modulation occurs in humans.
  
  
  METHODS
  We reviewed studies assessing immune status at different times of the year, restricting our review to studies assessing any of the following three biomarkers: antibody responses following vaccination, delayed-type hypersensitivity responses following skin testing, and clinical responses following experimental infection.
  
  
  RESULTS
  After systematic review and critical appraisal of the literature, six separate studies were available for final discussion. These results indicate that human immunity does vary by season. In the tropical setting of West Africa, both cell mediated and humoral immune responses appear to be reduced in children during the rainy season. In the tropical setting of Bangladesh, cell mediated immune responses also appear to be reduced in children during the rainy season. In the temperate setting of Russia, resistance to influenza infection appears to be reduced in young adults during winter.
  
  
  CONCLUSIONS
  Seasonal variation in immunity appears to occur in humans, and it is plausible that this variation may contribute to the seasonality of respiratory infections. Further research to assess the extent of seasonal immune modulation is required. We outline a number of recommendations to minimise bias in future studies.
authors.affiliation: School of Population Health, University of Queensland, Brisbane, Australia. Electronic address: s.paynter@uq.edu.au.
authors.forename: Stuart
authors.initials: S
authors.lastname: Paynter
authors.affiliation: School of Population Health, University of Queensland, Brisbane, Australia; Queensland Children's Medical Research Institute, University of Queensland, Brisbane, Australia.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Ware
authors.affiliation: Queensland Children's Medical Research Institute, University of Queensland, Brisbane, Australia.
authors.forename: Peter D
authors.initials: PD
authors.lastname: Sly
authors.affiliation: School of Population Health, University of Queensland, Brisbane, Australia.
authors.forename: Gail
authors.initials: G
authors.lastname: Williams
authors.affiliation: Faculty of Science, University of Adelaide, Adelaide, Australia; School of Pharmacy and Health Sciences, University of South Australia, Adelaide, Australia.
authors.forename: Philip
authors.initials: P
authors.lastname: Weinstein
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000917:Antibody Formation / Q000276:immunology; D015415:Biomarkers; D002648:Child; D002675:Child, Preschool; D004777:Environment; D005260:Female; D006801:Humans; D006968:Hypersensitivity, Delayed / Q000276:immunology; D055633:Immune System Phenomena / Q000502:physiology; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D011891:Rain; D012621:Seasons; D012737:Sex Factors; D012882:Skin Tests; D014329:Tropical Climate; D014612:Vaccines / Q000276:immunology*; D055815:Young Adult
chemical_list: D015415:Biomarkers; D014612:Vaccines
keywords: Epidemiology; Immune system; Seasons