immune system

common types of pathogens:

• living organisms:

  • parasites: unicellular and multicellular eukaryotes (e.g., tapeworms).

  • protozoa: malaria.

  • fungi: unicellular and multicellular eukaryotes (e.g., athlete’s foot).

  • bacteria: unicellular prokaryote (e.g. leprosy).

• non-living organisms:

  • virus: HIV

  • prion: misfolded proteins (e.g., CID).

lymphatic organs:

• lymph vessels:

  • network of vessels, similar to veins.

    • begins as blind-ended lymphatic capillaries.

  • lymphatic vessels transport lymph.

  • lymph is a milky fluid containing:

    • white blood cells

    • protein

    • fats

    • occasionally bacteria and viruses.

  • eventually drain into cardiovascular system through right lymphatic duct and thoracic dust.

lymph nodes cleanse the lymph:

• lymph nodes filter lymph, trapping germs and abnormal cells.

• contains macrophages and lymphocytes that destroy invaders.

• cleaned lymphs leave nodes and return to the blood stream.

spleen = largest organ in the lymphatic system.

• filters old red blood cells and fights infection.

• red pulp: cleans blood + stores it for emergencies.

• white pulp: immune cells scan for germs.

thymus gland causes t lymphocytes to mature.

• thymus gland:

  • located behind the sternum, above heart.

  • site of maturation of t cells (t lymphocytes)

  • secretes 2 hormones that control t cell development: thymosin & thymopoietin.

  • largest, most active during childhood.

  • atrophies with age.

• tonsils: filters food and air enters the throat.

• adenoids: filter air, back of nasal passages.

nonspecific defense: 2nd line of defense.

• phagocytic cells: white blood cells that surround and engulf invading bacteria.

  • neutrophils: first responders (blood, bacteria).

  • macrophages: leave blood and enter tissue (viruses, parasites).

  • eosinophils: (large parasites)

• inflammation: any injury will trigger inflammation as a way the body quickly deals with infection.

  • redness: dilation from histamine mast cells. more blood cells make it red.

  • swelling: histamines cause the blood cells to become leaky.

  • heat: warmth blood flows to the injured area.

  • pain: more fluid from swelling presses against the nerves.

• natural killer cells: a type of lymphocyte that attacks tumour cells.

• interferons: antiviral proteins.

• fever responses: pyrogens.

lymphocytes are central to specific defenses:

• b lymphocytes: antibody mediated immunity.

  • antibody and proteins made by b lymphocytes that bind with and neutralise specific antigens.

  • active against viruses, bacteria, and soluble foreign molecules.

  • t lymphocytes: cell-mediated immunity.

    • directly attacks foreign cells.

    • coordinate the immune response.

    • active against parasites, viruses, fungi, intracellular bacteria, cancer cells, cells with ‘non-self’ MHC.

antibody production by b cells.

• b cells made in bone marrow, travel to lymphatic tissue,

• each has a unique receptor, matches a specific antigen.

• b cells are activated when the pathogen’s antigen matches a b cell receptor.

• the b cells grow and divide.

• some of the ‘clones'' become plasma cells, secreting antibodies.

• other clones become memory b cells– long-term immunity.

t cells: cell-mediated immunity

• cytotoxic t cells have co8 receptors.

• activated by APCs.

• undergo clonal expansion.

• cdb+ cells directly kills abnormal or cancerous cells by releasing toxic chemicals.

• activated cdb+ cells patrol the body, searching for matching antigens.

• some cytotoxic cells become memory cells.

immune memory creates immunity

• primary immune response

  • occurs on first exposure to antigen

  • characteristics:

    • lag time of 3-6 days for antibody production.

    • peaks at 10-12 days.

• secondary immune response

  • occurs on second and subsequent exposure to antigen.

  • characteristics:

    • lag time is hours.

    • peaks in days.

    • much more antibody produced.

tissue rejection: may occur following tissue or organ transplant if recipient’s immune system attacks the transplanted tissue/organ.

• to minimise risk of rejection.

  • must match ABO and other blood group antigens and MHC antigens.

  • 75% MHC match is essential

    • MHC antigens allow body to distinguish ‘self’ from ‘non-self’

• immunosuppressive drugs prevent patient’s immune system from attacking transplanted organ.

allergies: hypersensitivity reactions.

• inappropriate response to an allergen.

• allergen: any substance (antigen) that causes an allergic reaction (not a pathogen, but the body reacts as though it’s a pathogen).

• excessive inflammatory response.

autoimmune disorders:

• inability of immune system to distinguish ‘self’ from ‘non-self’

• autoantibodies and cytotoxic cells target the body’s own tissues.