Innate Immunity: Physical Barriers and Mediators

• Immunity is the body's ability to resist damage from foreign substances like microorganisms and harmful chemicals, including internal threats like cancer.

Innate Immunity

• The body's response to foreign substances is the same each time it's exposed.
• Accomplished through physical barriers, chemical mediators, white blood cells, and the inflammatory response.

Physical Barriers

• Skin and mucous membranes prevent microorganisms and chemicals from entering the body.
• Tears, saliva, and urine wash away these substances.

Chemical Mediators

• Molecules responsible for many aspects of innate immunity.
• Chemicals on the surface of cells kill microorganisms or prevent their entry.

Complement

• Approximately 20 proteins in the plasma that circulate in an inactive form.
• Activated by combining with foreign substances or antibodies.
• Activated proteins promote inflammation, phagocytosis, and can directly lyse bacterial cells.

Interferons

• Proteins that protect against viral infections.
• Viruses stimulate infected cells to produce interferons.
• Interferons bind to neighboring cells, stimulating them to produce antiviral proteins.

White Blood Cells

• The most important cellular components of immunity.
• Chemicals attract WBC to damaged tissues, a process called chemotaxis.
• Chemicals that attract WBC are leukotrienes, kinins, histamine.

Phagocytic Cells

• Phagocytosis is the ingestion and destruction of particles by phagocytes.
• Neutrophils and macrophages are vital phagocytes.

Neutrophils

• Neutrophils are small phagocytic cells that are the first to enter infected tissues from the blood in large numbers.
• Often die after phagocyting a single microorganism.

Pus

• Pus is an accumulation of fluid, dead neutrophils, and other cells at a site of infection.

Macrophages

• Macrophages are monocytes that leave the blood, enter tissues, and enlarge.
• Monocytes and macrophages form the mononuclear phagocytic system.

Cells of Inflammation

• Basophils are motile white blood cells that can leave the blood and enter infected cells.
• Mast cells are non-motile cells in connective tissue, especially near capillaries.
• Both basophils and mast cells release chemicals such as histamine and leukotrienes, that produces inflammatory responses.

Natural Killer (NK) Cells

• Lymphocytes produced in red bone marrow account for up to 15% of lymphocytes.
• Recognize classes of cells, generally tumor cells or virus-infected cells, rather than specific ones.
• Do not exhibit a memory response.
• Use methods to lyse target cells, such as releasing chemicals that damage cell membranes.

Inflammatory Response

• Tissue damage leads to the release of chemical mediators like histamine, prostaglandins, leukotrienes, complement, and kinins.
• Vasodilation increases blood flow, bringing phagocytes and WBC to the area, allowing phagocytes to enter the tissue.
• Increased vascular permeability allows fibrinogen and complement to enter the tissue, fibrinogen turns to fibrin.
• Fibrin isolates the infection.
• Local Infection inflammatory response confined to a specific area of the body, leads to redness, heat, and swelling due to increased blood flow and vascular permeability
• Systemic Inflammation generally distributed throughout the body, with red bone marrow producing more neutrophils and pyrogens affecting body temperature-regulating mechanisms.

Adaptive Immunity

• Deals with specificity, ability to recognize a particular substance, and memory, the ability to respond with increasing effectiveness to successive exposures to the antigen.

Antigens

• Substances that stimulate adaptive immune response.
• Foreign antigens are introduced from outside the body and include bacteria, chemicals, and viruses.
• Self-antigens are molecules the body produces to stimulate an immune system response
• Antibodies are proteins produced in response to an antigen, also called gamma-globulins or immunoglobulins (Ig).

Antibody-Mediated Immunity

• Exposure of the body to an antigen leads to activation of B cells and the production of antibodies.
• Effective against extracellular antigens and is involved in allergic reactions.

Classes of Antibodies

• IgG activates the complement system and increases phagocytosis, and can cross placenta and provide immune protection to the fetus and newborn.
• IgM activates complement and acts as antigen-binding receptor on the surface of B cells, also responsible for transfusion reaction in the ABO blood system.
• IgA is secreted into saliva, tears, and onto mucous membranes to protect body surfaces.
• IgE binds to mast cells and basophils and stimulates the inflammatory response.
• IgD functions as an antigen-binding receptor on B cells.

Antibody Production

• Primary Response results from the first exposure of a B cell to an antigen, leading to the formation of plasma cells that produce antibodies.
• Memory B Cells are responsible for the secondary response, which occurs when the immune system is exposed to an antigen against which it has already produced a primary response.

Cell-Mediated Immunity

• The function of cytotoxic T cells and is most effective against microorganisms that live inside body cells, some allergic reactions, control of tumors, graft rejection.
• When viruses infect cells, some viral protein get broken down and become processed antigens that are combined with MHC class I molecules and displayed on the surface of the infectd cells, activation of cytotoxic T cell begins when the T-cell receptor binds to the MHC class I antigen.

Acquired Immunity

• Is immunity that develops during your lifetime.

Active Immunity

-Develops in response to an infection or vaccination.

• Natural immunity is when Antibodies developed in response to an infection
• Artificial Immunity is when Antibodies developed in response to a vaccination

Passive Immunity

• Develops after you receive antibodies from someone or somewhere else.
• Natural Immunity is when Antibodies received from a mother, e.g., through breast milk
• Artificial Immunity is when Antibodies received from a medicine, e.g., from a gamma globulin injection or infusion