Chapter 31: Assessment of Immune Function

The coordinated defense mechanism, known as the immune response, is typically described through three distinct actions: the phagocytic immune response, which is the first line of defense involving white blood cells like granulocytes and macrophages that engulf invaders; the humoral immune response (antibody response), which begins with B lymphocytes differentiating into plasma cells that produce antibodies; and the cellular immune response, which involves T lymphocytes that transform into cytotoxic T cells to directly attack pathogens. The overall response is a four-stage process: recognition of the foreign antigen, proliferation of sensitized T and B lymphocytes in lymphoid tissues like the lymph nodes, response, where differentiated cells perform their specific functions (antibody production or direct attack), and finally the effector stage, where the antigen is neutralized, often with the help of the complement system. Key components of cellular immunity include helper T cells (CD4+), which regulate and activate the immune system by secreting nonantibody proteins called cytokines, and cytotoxic T cells (CD8+), which cause cell lysis. Humoral immunity utilizes five main immunoglobulin classes: IgG, the major immunoglobulin in blood and tissues that crosses the placenta; IgA, which protects mucosal surfaces in body fluids; IgM, the primary antibody produced during initial infections; and IgE, associated with allergic and parasitic responses. Immune function is profoundly affected by numerous variables, including the aging process (referred to as immunosenescence), which results in impaired T-cell activation and decreased NK cell cytotoxicity, and nutritional status, where deficiencies in protein, zinc, or vitamins can severely suppress immune responses. Clinical assessment involves evaluating the patient's nutritional status, history of infections and immunizations, chronic illnesses, and exposure to factors like tobacco, alcohol, or immunosuppressive medications (e.g., high-dose antibiotics or corticosteroids). Furthermore, the chapter introduces advanced therapeutic concepts, including immunomodulators like interferons and colony-stimulating factors, as well as the emerging roles of monoclonal antibodies and genetic engineering in treating immune dysfunctions such as autoimmunity, hypersensitivity, and immune deficiencies.