Understanding the Immune System

The Immune System

• Immunity refers to the body's specific protective response to a foreign agent or organism, offering resistance to infectious diseases.
• Immunopathology studies diseases resulting from immune system dysfunction.
• Bone marrow produces T cells and B cells as components of the immune system.
• Spleen and lymph nodes are lymphoid tissues and components of the immune system.

Maturity of Lymphocytes

• B lymphocytes mature in the bone marrow.
• T lymphocytes mature in the thymus and differentiate into cells with various functions.

Function of the Immune System

• The immune system maintains homeostasis by removing foreign antigens like viruses and bacteria.
• Phagocytosis involves monocytes engulfing and destroying foreign bodies and toxins.
• The inflammatory response is triggered by injury or invading organisms.
• Chemical mediators minimize blood loss, confine invading organisms, activate phagocytes, and promote scar tissue formation and tissue regeneration.

Immunity

• Natural immunity gives a nonspecific response to any foreign invader.
  • White blood cells release mediators such as histamine, bradykinin, and prostaglandins, and engulf foreign substances.
  • Includes inflammatory responses and physical barriers, like intact skin, chemical barriers, and acidic secretions.
• Acquired immunity provides a specific defense against a foreign antigen through prior exposure.
  • This immunity can be active or passive.

Active and Passive Immunity

• Active immunity develops immunologic defenses within an individual's own body and lasts for many years, potentially a lifetime.
• Passive immunity is temporary and results from the transfer of immunity from an external source, such as through previous disease, immunization, transfer of antibodies from mother to infant, or immune globulin injections.

Four Stages in Immune Response

• Recognition: Identifying antigens as foreign.
• Proliferation: Stimulating the activation and division of lymphocytes.
• Response: Launching attacks to microbes.
• Effector: Actions of antibodies and cytotoxic T cells.

Recognition Stage

• Recognizes antigens as foreign entities using lymph nodes and lymphocytes for surveillance.
• Lymphocytes recirculate between the blood, lymph nodes, and bloodstream continuously.
• Macrophages aid in processing antigens by circulating lymphocytes.
• Macrophages and neutrophils possess receptors for antibodies and complement, and enhances phagocytosis by coating microorganisms.

Proliferation Stage

• Circulating lymphocytes containing antigenic messages return to the nearest lymph node.
• Resident T and B lymphocytes are stimulated to enlarge, divide, and proliferate.
• T lymphocytes differentiate into cytotoxic T cells.
• B lymphocytes produce and release antibodies.

Response Stage

• Commences with B lymphocytes producing antibodies in response to a specific antigen.
• Cellular responses stimulate resident lymphocytes to attack microbes, specifically killer T cells.
• Viral antigens, rather than bacterial, tend to induce a cellular response.
• Most responses to antigens involve both humoral and cellular responses, with one typically predominating.

Effector Stage

• Humoral immunity involves an interplay of antibodies.
• Cellular immunity involves action by cytotoxic T cells.

Response to Invasion

• Phagocytic immune response involves WBCs ingesting foreign particles and destroying invading agents, involving apoptosis (programmed cell death).
• Humoral/antibody response involves B lymphocytes transforming into plasma cells to manufacture antibodies.
• Cellular immune response uses T lymphocytes as cytotoxic killer cells to attack pathogens.

Humoral Immune Response

• Antigen recognition involves B lymphocytes responding to antigens by triggering antibody formation.
• Antibodies include Immunoglobulins like IgA, IgD, IgE, IgG, and IgM, which defend against foreign invaders through agglutination and opsonization.
• Antigen-antibody binding involves an antigenic determinant.

Cellular Immune Response

• T lymphocytes provide cellular immunity.
  • They directly attack invaders, secrete cytokines, and stimulate immune system responses.
  • Involves Helper T cells, Cytotoxic T cells, Memory cells, and Suppressor T cells.

Non-T and Non-B Lymphocytes Involved in Immune Response

• Null cells destroy antigens coated with antibodies.
• Natural killer cells defend against microorganisms and some malignant cells.

Complement System

• Circulating plasma proteins made in the liver activate when antibodies connect to antigens, playing a key role in defense against microbes.
• Activated by classic, lectin, and alternative pathways.
• Has three key functions.
  • Defense against bacterial infection.
  • Bridging natural and acquired immunity.
  • Disposal of immune complexes and by-products.

Variables that Effect Immune System Function

• Age and gender
• Nutrition
• History of infection or immunization
• Allergies
• Conditions or disorders like autoimmune disorders, cancer, chronic illness, surgery or trauma
• Medications and transfusions
• Lifestyle
• Psychoneuroimmunologic factors

Advances in Immunology

• Genetic engineering through DNA technology.
• Stem cell research indicates stem cells can restore destroyed immune systems.
  • Clinical trials using stem cells are underway for autoimmune disorders like lupus, rheumatoid arthritis, scleroderma, and multiple sclerosis.
  • These opportunities present ethical challenges.

Assessment of the Immune System

• Review the health history, including nutrition, infections, immunizations, allergies, autoimmune disorders, cancer, and chronic illness.
• Perform a physical exam: lymph node assessment and skin examination.

Tests to Evaluate Immune Function

• WBC count and differential
• Bone marrow biopsy
• Humoral and cellular immunity tests
• Phagocytic cell function test
• Complement component tests
• Hypersensitivity tests
• Specific antigen-antibody tests
• HIV infection tests

Nurse's Role in Evaluation of the Immune System

• Offering support
• Reducing anxiety
• Providing patient education and counseling