HLA CLASS-II GENES IN SOYBEAN EPIDEMIC ASTHMA PATIENTS

From 1981 to 1987, 26 outbreaks of asthma caused by the inhalation of soybean dust, affecting a total of 688 individuals, were detected in B arcelona, Spain. Because only a small proportion of asthmatic individu als living in Barcelona expressed the epidemic phenotype, it is hypoth esized that a genetically determined human leukocyte antigen (HLA) Cla ss II factor could have played a role in the susceptible individuals. Accordingly, we studied the distribution of both HLA-DR and HLA-DQ in soybean epidemic asthmatic patients. An analysis of the HLA-DR and HLA -DQ genes for genetic polymorphisms of the pi chain was done with the polymerase chain reaction (PCR) in 78 soybean epidemic asthma patients , and the findings were compared with those for 67 nonepidemic asthmat ic individuals and 168 individuals from the general population. An all elic disequilibrium could be established; the risk of epidemic asthma was particularly associated with the DRB113 gene (p value corrected f or multiple comparisons < 0.02). The association observed for the DRB1 13 gene was stronger in individuals in the lowest tertile for total I gE, with an estimated risk with a 95% confidence interval (CI), of 14. 5 (1.6 to 130.8). The combination of two genes from among the DRB105- 05, DRB105-06, and DRB1*06-06 genes was present in epidemic asthmatic subjects only. No association with an HLA-DQB1 allele could be observ ed. Genetic predisposition could contribute to the response of some as thmatic patients to exposure to soybean dust, having led to their bein g affected during the epidemics of asthma in Barcelona.