title: Combined effects of smoking, anti-EBNA antibodies, and HLA-DRB1*1501 on multiple sclerosis risk.
abstract: OBJECTIVE
  To examine the interplay between smoking, serum antibody titers to the Epstein-Barr virus nuclear antigens (anti-EBNA), and HLA-DR15 on multiple sclerosis (MS) risk.
  
  
  METHODS
  Individual and pooled analyses were conducted among 442 cases and 865 controls from 3 MS case-control studies-a nested case-control study in the Nurses' Health Study/Nurses' Health Study II, the Tasmanian MS Study, and a Swedish MS Study. Conditional logistic regression models were used to calculate odds ratios (ORs) and 95% CIs for the association between smoking, anti-EBNA titers, HLA-DR15, and MS risk. Study estimates were pooled using inverse variance weights to determine a combined effect and p value.
  
  
  RESULTS
  Among MS cases, anti-EBNA titers were significantly higher in ever smokers compared to never smokers. The increased risk of MS associated with high anti-EBNA Ab titers was stronger among ever smokers (OR = 3.9, 95% CI = 2.7-5.7) compared to never smokers (OR = 1.8, 95% CI = 1.4-2.3; p for interaction = 0.001). The increased risk of MS associated with a history of smoking was no longer evident after adjustment for anti-EBNA Ab titers. No modification or confounding by HLA-DR15 was observed. The increased risk of MS associated with ever smoking was only observed among those who had high anti-EBNA titers (OR = 1.7, 95% CI = 1.1-2.6).
  
  
  CONCLUSIONS
  Smoking appears to enhance the association between high anti-EBNA titer and increased multiple sclerosis (MS) risk. The association between HLA-DR15 and MS risk is independent of smoking. Further work is necessary to elucidate possible biologic mechanisms to explain this finding.
authors.affiliation: Departments of Nutrition, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Simon
authors.forename: I A F
authors.initials: IA
authors.lastname: van der Mei
authors.forename: K L
authors.initials: KL
authors.lastname: Munger
authors.forename: A
authors.initials: A
authors.lastname: Ponsonby
authors.forename: J
authors.initials: J
authors.lastname: Dickinson
authors.forename: T
authors.initials: T
authors.lastname: Dwyer
authors.forename: P
authors.initials: P
authors.lastname: Sundström
authors.forename: A
authors.initials: A
authors.lastname: Ascherio
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D019309:Epstein-Barr Virus Nuclear Antigens / Q000276:immunology*; D005260:Female; D006684:HLA-DR Antigens / Q000235:genetics* / Q000276:immunology; D059811:HLA-DRB1 Chains; D006239:Haplotypes; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000209:etiology* / Q000276:immunology; D016017:Odds Ratio; D012306:Risk; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects* / Q000276:immunology
chemical_list: D019309:Epstein-Barr Virus Nuclear Antigens; D006684:HLA-DR Antigens; D059811:HLA-DRB1 Chains; C489631:HLA-DRB1*15:01 antigen