Environmental factors and immune related outcomes in the United States

Abstract

Environmental factors have been found to be important risk factors of human health. Previous studies suggested that PM2.5 could perturb the immune system. PM2.5 is complex mixture of multiple constituents, and each of these constituents could have varying impact on health. However, most existing studies treated PM2.5 as a single exposure. How each of the constituents affects the immune system is less clear. Non-optimal temperature is another environmental factor that could potentially impair the immune function of human body. While the effects of mean temperature have been extensively studied, the influence of temperature variability—particularly over longer time periods—remains insufficiently explored. In this dissertation, we attempted to address these gaps. We began by studying the association between long-term exposure to PM2.5, PM2.5 constituents, source-specific PM2.5 and hospital admissions from non-respiratory infections among the Medicare beneficiaries in the US between 2000-2016. We found that PM2.5 was associated with increased risk of hospital admissions from total non-respiratory infections and its subtypes including intestinal infections, urinary tract infections and septicemia. Sulfate, nickel and copper contributed the largest weights in the association between PM2.5 and non-respiratory infections. Anthropogenic sources of PM2.5 were found to have the largest impact on the exposure-outcome associations. In chapter II, we studied the association between seasonal temperature variability, seasonal temperature and hospital admissions from infections using an adapted difference-in-difference analysis among the Medicare beneficiaries. We found that increased temperature variability in both warm and cold season, higher mean temperature in warm season and lower mean temperature in cold season were associated with increased admissions from infections. In the last chapter, we shifted our focus from the older population to an immunocompromised group— kidney transplant recipients. Here we investigated the association between exposure to PM2.5 constituents prior to kidney transplant (KT) and post-KT outcomes including acute rejection, delayed graft function, graft failure and mortality. We found that sulfate contributed the larges weight in the association between the PM2.5 mixture and long-term post-KT outcomes (graft failure and mortality) while lead, organic carbon and nickel contributed the largest weights in the short-term outcomes (delayed graft function and acute rejection). This dissertation contributes to the growing body of evidence on the impact of environmental exposures on the immune system. It further demonstrates that the health effects of PM2.5 can vary depending on its chemical constituents and specific sources. Overall, this work provides important insights into the broader health implications of air pollution and climate change on human populations.