Exposure associated with tripled risk
(Reuters) — Exposure to textile dust among women in Malaysia — a common occupational occurrence — was associated with an almost tripled risk of developing rheumatoid arthritis (RA), and the increased risk was seen for both seropositive and seronegative disease, a population-based case-control study found.
Among participants in the Malaysian Epidemiologic Investigation of Rheumatoid Arthritis (MyEIRA) who reported occupational exposure to textile dust, the odds ratio for developing RA was 2.8 (95 per cent CI 1.6-5.2), according to Chun Lai Too, PhD, of the Institute for Medical Research in Kuala Lumpur, and colleagues.
For those who were positive for anticitrullinated peptide antibody (ACPA), the odds ratio was 2.5 (95 per cent CI 1.3-4.8), while for those who were ACPA negative, the odds ratio was 3.5 (95 per cent CI 1.7-7), the researchers reported online in Annals of the Rheumatic Diseases.
Cigarette smoking has been clearly established as a risk factor for RA, particularly among individuals who are carriers of the HLA-DRB1 shared epitope gene alleles. "There is growing support for the hypothesis that this gene-environment interaction may induce changes in the lung tissues, where immunity against citrullinated antigens may be triggered in individuals with certain genotypes," they wrote.
Silica exposure also has been implicated in RA risk, suggesting that other inhaled substances could have similar immune effects in the lung.
One such possibility is textile dust, which has been linked with respiratory problems in workers, but whether the effects on the lungs could extend to triggering RA has not previously been explored.
The MyEIRA study included 910 women with RA and an equivalent number of control women whose mean age was 47.
Men were not included in the analysis because very few had occupational exposure to textile dust. In addition, almost half of men with RA smoked, which could influence their risk, while almost none of the women smoked.
Two-thirds of the cases were ACPA positive and 40 per cent were carriers of the HLA-DRB1 shared epitope, compared with only 2 per cent and 16 per cent of controls, respectively.
Occupational exposure was reported by 4.5 per cent of cases and 1.7 per cent of controls.
The risk of ACPA-positive RA was particularly pronounced among women who were carriers of the HLA-DRB1 alleles and who were exposed to textile dust, with an odds ratio of 39.1 (95 per cent CI 5.1-297.5). In addition, a significant interaction between being a carrier of the shared epitope alleles and exposure was seen, and an attributable proportion of 0.8 (95 per cent CI 0.5-1.2, P<0.0001) for ACPA-positive RA.
Women who were HLA-DRB1 carriers and exposed to textile dust also had an increased risk of ACPA-negative RA, with an odds ratio of 9.3 (95 per cent CI 1-89.4), but no significant interaction between the two factors was seen.
The finding that exposure to textile dust was associated with both ACPA-positive and ACPA-negative RA differed from what has been seen for smoking and silica exposure, which have been linked only with ACPA-positive disease.
"We do not have any mechanistic hypothesis for this difference and can only speculate that textile dust exposure may have a more general effect on immune activation," the researchers wrote.
They noted that different types of textiles can have various characteristics, depending on whether of natural or synthetic origin and the processing methods used in manufacture.
"The association between textile dust and risk of RA might involved several potential disease mechanisms since the differing physicochemical properties of airborne dust affect where it deposits in the respiratory tract," they explained.
There also may be other potentially toxic workplace exposures involved in textile manufacturing, such as asbestos and solvents.
Bacteria present in textile dust could further contribute, possibly through production of endotoxin by Gram-negative species that can lead to pulmonary inflammation.
"From a public health perspective, our results imply that efforts should be considered to reduce the incidence of RA by reducing occupational exposure to textile dust," the authors concluded.
Limitations of the study included a lack of information about passive smoke exposure and other workplace hazards, as well as the possibility of selection bias.
The study was funded by the Ministry of Health Malaysia and the Swedish National Research Council.
The authors reported no financial conflicts.
