Environmental toxicants and the developing immune system: a missing link in the global battle against infectious disease?

Abstract

There is now compelling evidence that developmental exposure to chemicals from our environment contributes to disease later in life, with animal models supporting this concept in reproductive, metabolic, and neurodegenerative diseases. In contrast, data regarding how developmental exposures impact the susceptibility of the immune system to functional alterations later in life are surprisingly scant. Given that the immune system forms an integrated network that detects and destroys invading pathogens and cancer cells, it provides the body's first line of defense. Thus, the consequences of early life exposures that reduce immune function are profound. This review summarizes available data for pollutants such as cigarette smoke and dioxin-like compounds, which consistently support the idea that developmental exposures critically impact the immune system. These findings suggest that exposure to common chemicals from our daily environment represent overlooked contributors to the fact that infectious diseases remain among the top five causes of death worldwide.

Figure 1. Lower respiratory tract infections are among the top five causes of death worldwide

Data are adapted from a recent WHO report on the global burden of disease [1]. Data are based on information from 2004, in which an estimated 59 million people died, with 4.2 million deaths attributed to lower respiratory tract infections, and at least another 7 million deaths due to other infectious diseases. The primary differences between affluent and poor countries with respect to antecedents of mortality are that in low income countries, the major causes of death are infectious diseases, and over 1/3 of all deaths are children under 14 years of age. In middle income countries, chronic diseases begin to contribute to major causes of death; however tuberculosis remains a major source of morbidity and mortality. In high income countries, nearly half the population lives to 70 years of age and chronic illnesses predominate as major causes of death; although lower respiratory tract infections persist among the top 5 killers even in the world’s most affluent nations.