Exposure to wood smoke can have different effects on the respiratory immune systems of men and women, according to a study at the UNC School of Medicine.
The scientists exposed men and women volunteers to wood smoke prior to inoculating them with a standard dose of the influenza virus vaccine, which causes a natural, yet mild, immune response in the nasal passages. They then later discovered that the men exposed to wood smoke had significantly higher markers of an inflammatory response in cells that line the nasal passages relative to men exposed to filtered air. By contrast, for women, the wood smoke exposure appeared to lower markers of the inflammatory response. When the researchers averaged out the data from men and women, as these sorts of exposure studies typically do, the analysis gave the false impression that the wood smoke had almost no effect on the immune response to the live-attenuated influenza virus vaccine.
Wood smoke is among the most ancient environmental pollutants and is still considered a significant cause of sickness and death today. Researchers estimate that about 40 percent of the modern human population, roughly three billion people, are chronically exposed to smoke from burning wood and related “biomass” combustibles, such as leaves, crop stalks, and dung. Wood smoke contains dozens of known toxins, and epidemiological studies have linked biomass exposures to chronic obstructive pulmonary disorder in women who have never smoked and lung cancer in male firefighters. Wood smoke exposure is also expected to become more common as the frequency of wildfires increases.
Epidemiological studies have suggested that wood smoke impairs normal lung functions and the ability of the human airway to defend itself against respiratory infections. But controlled exposure studies directly linking wood smoke exposure and altered responses to respiratory infections had not been completed.
The scientists aren’t yet sure why men and women would differ so starkly in their immunological responses to wood smoke. One possibility is that women and men over thousands of generations have had different evolutionary histories of wood smoke exposure, leading to different evolutionary adaptations. Women, for example, might have had greater and more chronic exposure to smoke from cooking fires, compared to men. Other factors that may have influenced the sex-specific responses include differences in male and female hormone profiles and genetics.
Regardless, this study suggests that any research on environmental exposures should take potential gender differences into account.