9.2 Recorded Lecture - Innate and Acquired Immunity

• Immunity is acquired in two types: innate and acquired.

Innate Immunity

• Involves phagocytosis of bacteria.
• Destruction of swallowed organisms through stomach acid.
• Use of the complement complex, a system of about 20 proteins activated to destroy bacteria.
• Natural killer lymphocytes recognize and destroy foreign cells.

Acquired Immunity

• Initiated by antigens
• Antigens are compounds different from all other compounds in the body.
• Humoral acquired immunity develops globulin molecules in blood plasma, attacking the invading agent.
• Cell-mediated immunity involves a large number of activated T lymphocytes in lymph nodes destroying a foreign agent.
• Lymphocytes are mostly in lymph nodes, but also in the spleen, GI tract, thymus, and bone marrow.
• Individuals born without lymphocytes die shortly after birth from bacterial infection.

T and B Lymphocytes

• T lymphocytes are responsible for cell-mediated immunity.
• T lymphocytes start in bone marrow and migrate to the thymus gland.
• In the thymus they divide rapidly and develop diversity for reacting against specific antigens.
• B lymphocytes provide moral immunity.
• B lymphocytes originate in the liver during mid-fetal life and in bone marrow in late fetal life and after birth.
• Activated T and B lymphocytes become T and B cells, reacting specifically against antigens.
• Activated lymphocytes reproduce, forming duplicates responsive to a single type of antigen, and are released into the lymph for months to years.
• B lymphocytes produce antibodies formed by plasma cells.
• B lymphocytes remain dormant in lymphoid tissue until exposure to a specific antigen.
• Upon exposure, they enlarge and become lymph blasts, differentiating into plasma blasts.
• Plasma blast produce gamma globulin antibodies, secreted into the lymph.
• Some B lymphocytes form memory cells instead of plasma blasts.
• Memory cells circulate through the body to lymphoid tissue, remaining dormant until activated by the same agent.
• The secondary response is more potent and forms antibodies for months, unlike the primary response.
• Memory cells can provide lifelong immunity against infectious diseases like measles and smallpox.
• High titers of smallpox antibodies have been detected in vaccinated subjects 70 years prior.

Antibodies

• Antibodies are gamma globulins called immunoglobulins.
• Immunoglobulins constitute about 20% of all plasma proteins.
• Each antibody is specific for a particular antigen due to its structure.
• Five general classes of antibodies: AGM, IGG, IGA, IGD, and IGE.
• Antibodies protect the body through direct attack or by activating the complement system.

T Cells

• When T lymphocytes are activated, they form T cells, with responses that are antigen-specific.
• Helper T cells are the most numerous, making up 75% of T Cells.
• Helper T cells aid immune system functions by forming protein mediators.
• The immune system can be paralyzed without helper T cells.
• HIV inactivates or destroys the helper T cell.

Autoimmune Disease

• Autoimmune diseases occur when acquired immunity destroys an individual's own body.
• Tolerance develops during the pre-processing of lymphocytes.
• Immune tolerance loss to one's own tissue can occur in older people or after tissue destruction.
• Over 100 autoimmune diseases have been described with main examples including:
  • Rheumatoid arthritis
  • Glomerulonephritis
  • Myasthenia gravis
  • Lupus erythematosus
  • Thrombocytopenia

Immunization

• Immunization is used to produce acquired immunity against specific diseases.
• Immunization can be achieved through:
  • Injecting dead organisms
  • Injecting live, weakened organisms
  • Injecting toxins that have been treated to destroy their toxic properties
• The commonality between all three is maintaining their antigens to create immunity.
• Passive immunity can be achieved through antibodies or activated T cells from another animal that has been actively immunized.
• These antibodies typically only last for 2-3 weeks.

Allergy and Hypersensitivity

• Delayed reaction allergies are caused by activated T cells, not antibodies.
• In poison ivy exposure, a T cell-mediated immune reaction occurs, causing harm.
• Atopic allergies are caused by unusual responses of the immune system.
• Allergic tendencies are genetically passed and characterized by IgG antibodies.
• IgG antibodies attach to mast cells and basophils.
• When an antigen is present, the antibody causes the mast cell or basophil to rupture, releasing inflammatory agents like histamine, heparin, and platelet activating factors.
• Anaphylaxis is a widespread allergic reaction caused by basophils and mast cells sensitized by IgG reagents.
• Histamine is released in circulation, causing vessel dilation and increased capillary permeability.
• Slow-reacting substance of anaphylaxis causes spasms in the smooth muscle of the bronchioles, eliciting an asthma-like attack.