Disorders of the Immune System

Disorders of the Immune System

Disorders of the Immune System

Normal Immune System Structure and Function

  • Function of immune system is to protect the host from invasion of foreign organisms by distinguishing “self” from “non-self.”
  • Necessary for survival
  • Prevents and repels attacks from external factors and endogenous factors
  • Normal immune response relies on careful coordination of complex network or biological factors, specialized cells, tissue, and organs necessary for recognition of pathogens and subsequent elimination of foreign antigens



Anatomy of the Cells of the Immune System

  • Consists of both antigen-specific and nonspecific components
  • Major cellular components of the immune system consist of monocytes and macrophages, lymphocytes, and the family of granulocytic cells (including neutrophils, eosinophils, and basophils).
  • Mononuclear phagocytes participate in antigen processing, tissue repair, and secretion of mediators vital to initiation of specific immune responses
  • Lymphocytes are responsible for the initial specific recognition of antigen
  • Cytotoxic or “killer” T cells (CTLs) are responsible for defense against intracellular pathogens
  • Neutrophils phagocytose and destroy foreign antigens and microbial organisms
  • Eosinophils play a crucial role in the host’s defense against parasites; considerably less efficient than neutrophils at phagocytosis
  • Basophils play an important role in both immediate- and late-phase allergic responses
  • Mast cells are basophilic straining cells; source of many mediators of immediate hypersensitivity

Organs of the Immune System

  • Bone marrow is where all cells of the immune system are originally derived
  • Thymus functions to produce T lymphocytes and is the site of initial T-lymphocyte differentiation
  • In mammals, the lymph nodes, spleen, and gut-associated lymphoid tissue are secondary lymphoid organs connected by blood and lymphatic vessels

Inflammatory Mediators

  • Preformed mediators include histamine, eosinophil and neutrophil chemoattractants, proteoglycans (heparin, chondroitin sulfate) and various proteolytic enzymes.
  • Histamine is a bioactive amine; important in the pathogensis of allergic rhinitis, allergic asthma, and anaphylaxis


  • Innate and adaptive immunity
  • Living organisms exhibit two levels of response: innate system of natural immunity and an adaptive system that is acquired
  • Antigens (or immunogens)
  • Foreign substances that can induce an immune response
  • Immune Response
  • A complex network of specialized cells, organs, and biologic factors is necessary for the recognition and subsequent elimination of foreign antigens
  • Antigen Processing & Presentation
  • Most foreign immunogens are not recognized by the immune system in their native form and require capture and processing by professional APCs
  • T-Lymphocyte Recognition & Activation
  • The recognition of processed antigen by specialized T lymphocytes known as helper T (CD4) lymphocytes and the subsequent activation of these cells constitute the critical events in the immune response.
  • CD8 Effector Cells (Cellular Immune Response)
  • CTLs eliminate target cells thus constituting the cellular immune response
  • Activation of B Lymphocytes (Humoral Immune Response)
  • Primary function of mature B lymphocytes is to synthesize antibodies
  • Antibody Structure & Function
  • Five classes (isotypes) of immunoglobulins are IgG, IgA, IgM, IgD, and IgE
  • Humoral Mechanisms of Antigen Elimination
  • Antibodies induce elimination of foreign antigen through a number of different mechanisms.
  • Mechanisms of Inflammation
  • Cytokines and antibodies trigger the recruitment of additional cells and the release of endogenous vasoactive and proinflammatory enzymatic substances.
  • Hypersensitivity Immunes Responses
  • Classified into four distinct types of reactions
  • Synthesis of IgE in Allergic Reactivity
  • Allergic hypersensitivity results from the inappropriate and sustained production of IgE in response to allergen.

Pathophysiology of Allergic Rhinitis

  • Characterized by local tissue damage and organ dysfunction in the upper and lower respiratory tract arising from an abnormal hypersensitivity immune response to normally harmless and ubiquitous environmental allergens
  • Allergens that cause airway disease are predominantly seasonal tree, grass, and weed pollens or perennial inhalants (house dust mite antigen, cockroach, mold, animal dander)
  • Implies the existence of type I (IgE-mediated) immediate hypersensitivity to environmental allergens that impact the upper respiratory mucosa directly

Allergic Rhinitis

  • The interaction of mediators with various target organs and cells of the airway can induce a biphasic allergic response.
  • The early-phase response occurs within minutes after exposure to an antigen; after intranasal challenge or ambient exposure to relevant allergen, the allergic patient begins sneezing and develops an increase in nasal secretions.
  • The late-phase allergic response may follow the early-phase response or may occur as an isolated event; late-phase response is characterized by erythema, induration, heat, burning, and itching.
  • Symptoms appear immediately after exposure to a relevant allergen (early-phase response), although many patients experience chronic and recurrent symptoms on the basis of the late-phase inflammatory response.
  • Complications of severe or untreated allergic rhinitis include sinusitis, auditory tube dysfunction, hyposmia, sleep disturbances, asthma exacerbations, and chronic mouth breathing.

Disorders of the Immune System