Antinuclear Antibodies and Bromoxynil Exposure in a Rural Sample

Abstract

Previous research suggests that farmers may have an increased risk of developing autoimmunity and that exposure to certain pesticides may alter immune function. Little is known, however, about the immunologic effects of farming and pesticide exposures. As part of the Prairie Ecosystem Study, associations between detection of antinuclear antibodies (ANA), an autoimmunity indicator, and exposure to the herbicide bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) were investigated in a cross-sectional study of 208 residents (94 women, 114 men) of a cereal-producing region in Saskatchewan, Canada, during spring herbicide application, 1996. The ANA were assayed in serum by indirect immunofluorescence on HEp-2 cells. Bromoxynil was measured in plasma by gas chromatography/mass spectrometry analysis. Associations were explored between ANA detection and detection of bromoxynil in plasma, self-reported use of bromoxynil and other pesticides, farming exposures, gender, age, body mass index (BMI), and residency. The mean age (SD) of the participants was 50.8 (13.6) yr [women: 49.7 (13.5) yr, men: 51.6 (13.6) yr]. ANA prevalence was 37.5% (women: 39.4%, men: 36%,) at 1:40 serum dilution, 17.3% (women: 20.2%, men: 14.9%) at 1:80, and 10.1% (women: 13.8%, men: 7%) at 1:160. In the multiple-variable Generalized Estimating Equation (GEE) logistic regression analyses, female gender was a positive predictor of ANA detection and gender differences were observed in the relative importance of other study factors. None of the variables examined in the multiple-variable GEE analysis were statistically significant predictors of ANA detection for women. For many of these variables, however, the point estimates for women are similar to those seen in men. For men, with adjustment for age, ANA presence was inversely associated with detection of concentrations of bromoxynil in winter or spring samples and recent occupational use of 2,4-dichlorophenoxyacetic acid, and the positive ANA predictors included having a BMI in the obese (BMI > 30.04 kg/m²) category, recent occupational use of trifluralin or fungicides, and current exposure to oilseed, poultry, or dairy production. The inverse association between ANA detection and bromoxynil exposure observed in farmers in this study is consistent with earlier empirical observations that certain pesticides may suppress immune function. Further research is needed to examine whether these findings are confirmed in other populations and to elucidate the biological mechanisms involved.

Donald G. Irvine is deceased.

This research was funded in part by the Eco-Research Program, Tri-Council Secretariat, Canada through a grant (922-94-0009) for the Study of the Sustainability of the Semi-Arid Prairie Ecosystem (PECOS) and by the National Health Research Development Program, Health Canada through a National Health Research Scholar award (6608-1323-48) to Dr. Karen M. Semchuk. The authors gratefully acknowledge the support and key contributions made to the design and conduct of the study by the residents of the study area and by the following research team members: Dr. Darwin W. Anderson, Janice Colquhoun, Daphne M. Cordeiro, Dr. Margaret F.O. Crossley, Dr. James A. Dosman, Maura Gillis-Cipywnyk, Louise Hagel, Pat Hanke, Leslie Holfeld, Dr. Vic Laxdal, Donna Ledingham, Dr. Ambikaipakan Senthilselvan, Phyllis Snodgrass, and Dr. Taylor A. Steeves.