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The immune system lies at the intersection of the external environment and internal host organ systems and modulates these interactions to protect the host from damage and disease. Although much of the response is organized to protect against infectious diseases, some responses are also directed against environmental irritants and agents that can perturb host homeostatic processes. In some cases, an unchecked or dysfunctional immune response in reaction to certain occupational exposures plays an important role in causing occupational diseases. This chapter will review the basic components and functions of the immune system and then discuss in more depth common occupational diseases driven by innate and adaptive immune responses.


The basic function of the immune system is to protect the host from invasion or damage by foreign organisms, first by distinguishing “self” from “nonself” antigens, then by elaborating a protective response, and finally by turning off the response once the danger threat has been neutralized. In most cases, such a response is beneficial. The exposures that turn on the immune response are carefully defined, and the response is orchestrated along set pathways. In some settings, however, where the immune response is directed against either irrelevant or self-antigens, or is overly aggressive or not downregulated, the system can trigger tissue damage and disease in the host.

Immune responses can be broadly categorized into innate versus adaptive immunity. Broadly speaking, the innate response is designed for rapid pattern recognition and neutralization, whereas the adaptive response is more targeted and specific, and takes time to be elaborated.

Figure 15–1.

Overview of the Immune System.

As a general principle, consider the immune system to function similarly to the Marvel comics character Daredevil. While technically blind, the system is constantly sampling the environment by shape, size, pattern, ion fluxes, pH changes, and other signals to distinguish self from nonself, and friend from enemy, to initiate the most appropriate and best response.


Most living organisms, from bacteria and plants to humans, possess a rapid innate system of immune responses based on basic pattern recognition that automatically triggers defensive responses. Innate immunity is present from birth, and, importantly, does not require previous antigenic exposure for the response. Four main components are considered to constitute the innate immune system.

  1. Physical obstacles, including the intact skin and mucosal barriers of the gastro-intestinal and respiratory tracts, serve as the first line of defense. Colonization with beneficial bacteria, viruses, and fungi that constitute the normal human microbiome serve to limit availability of these potential ecological niches for growth of harmful organisms.

  2. Phagocytic barriers mediated by neutrophils, macrophages, and natural killer cells (NK cells) serve as the next level of protection. Neutrophils are the most abundant of circulating ...

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