title: Environmental conditions, immunologic phenotypes, atopy, and asthma: new evidence of how the hygiene hypothesis operates in Latin America.
abstract: BACKGROUND
  It has been proposed that improved hygiene and reduced experience of infections in childhood influences the development of allergic diseases. The mechanisms by which the hygiene operates are not well established but are underpinned by two apparently incompatible immunologic paradigms, the balance of TH1 versus TH2 cytokines and IL-10-mediated regulation of TH2 cytokines.
  
  
  OBJECTIVE
  This study defined immunologic phenotypes with the use of latent class analysis and investigated their associations with environmental factors, markers of allergy and asthma, in a Latin American population.
  
  
  METHODS
  We studied 1127 children living in urban Brazil. Data on wheeze and environmental exposures were collected with standardized questionnaires. Atopy was measured by specific IgE in serum and skin prick test reactivity to aeroallergens. Cytokines were measured in culture after the stimulation of peripheral blood leukocytes with mitogen. Infections with pathogens were assessed by serology and stool examinations. Children were classified as having high or low burden of infection. Latent class analysis was used to identify immune phenotypes on the basis of cytokine production. Logistic regression was used to evaluate the adjusted effects of environment and burden of infection on the immunologic phenotypes and the effect of the phenotypes on atopy and asthma.
  
  
  RESULTS
  Three phenotypes were identified, labeled underresponsive, intermediate, and responsive. Children of more educated mothers, living in improved environmental conditions, and with a low burden of infection were significantly more likely to have the responsive phenotype. The responsive phenotype was significantly associated with an increased prevalence of atopy but not asthma.
  
  
  CONCLUSIONS
  Our findings contribute to a better understanding of the immune mechanisms by which the hygiene hypothesis operates in urban Latin America.
authors: Instituto de Ciências da Saúde, Universidade Federal de Bahia, Salvador, Brazil.
authors: Camila Alexandrina
authors: CA
authors: Figueiredo
authors: Instituto de Matemática, Universidade Federal de Bahia, Salvador, Brazil.
authors: Leila D
authors: LD
authors: Amorim
authors: Instituto de Ciências da Saúde, Universidade Federal de Bahia, Salvador, Brazil.
authors: Neuza M
authors: NM
authors: Alcantara-Neves
authors: Instituto de Saúde Coletiva, Universidade Federal de Bahia, Salvador, Brazil.
authors: Sheila M A
authors: SMA
authors: Matos
authors: Molecular and Biochemical Parasitology, Liverpool School of Tropical Medicine, Liverpool and London, United Kingdom.|Colegio de Ciencias de La Salud, Universidad San Francisco de Quito, Quito, Ecuador.
authors: Philip J
authors: PJ
authors: Cooper
authors: London School of Hygiene and Tropical Medicine, United Kingdom.
authors: Laura C
authors: LC
authors: Rodrigues
authors: Instituto de Saúde Coletiva, Universidade Federal de Bahia, Salvador, Brazil.
authors: Mauricio L
authors: ML
authors: Barreto
mesh_terms: D000293:Adolescent; D000485:Allergens / Q000276:immunology; D001249:Asthma / Q000453:epidemiology / Q000276:immunology* / Q000473:pathology; D001938:Brazil / Q000453:epidemiology; D002648:Child; D016207:Cytokines / Q000276:immunology; D004777:Environment; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D006920:Hygiene; D061148:Hygiene Hypothesis; D006969:Hypersensitivity, Immediate / Q000453:epidemiology / Q000276:immunology* / Q000473:pathology; D007073:Immunoglobulin E / Q000276:immunology; D016130:Immunophenotyping; D016753:Interleukin-10 / Q000276:immunology; D008297:Male; D015995:Prevalence; D012882:Skin Tests; D011795:Surveys and Questionnaires; D058408:Th1-Th2 Balance; D014505:Urban Population
chemical_list: D000485:Allergens; D016207:Cytokines; D016753:Interleukin-10; D007073:Immunoglobulin E