BIO116- The Immune System

Defense mechanisms

Skin, stomach acid, tears and vomiting

Innate/non specific defense mechanisms

Phagocytosis, inflammation

Specific/adaptive defense mechanisms

Antibodies, T cells (immune response enables body to recognise, remove specific bacteria, other foreign cells, viruses)

Non specific responds to what?

Generalised pathogens and tissue damage

Specific responds to what?

Specific pathogens (responsible for long term immunity via memory cells of pathogens and ability to mount faster immune response)

Living pathogens?

Bacteria, fungi, parasites

Non-living infectious particles?

Viruses, prions

Transmissibility

How easily pathogen is passed on

Mode of transmission

Respiratory, oral-fecal, body fluids, direct contact

Virulence

How much damage is caused by the infection e.g viruses have easy transmission, but less virulent; AIDs are more virulent but harder to transmit

What is the lymphatic system?

Separate from arteries, capillaries, blood vessels and veins. Interstitial fluid leaks out of these, and the lymph nodes filter it for foreign microbes with lymph, returning it to the circulatory system again.

Basic components of the Lymphatic system

Lymph vessels, lymph nodes, spleen, thymus, tonsils and adenoids

Lymph is a milky fluid that contains…?

White blood cells, proteins, fats and occasionally bacteria and viruses

Filtered fluid is returned to circulatory/cardiovascular system via?..

Lymphatic vessels that begin as capillaries, through the right lymphatic duct and the thoracic duct

Lymph nodes contain lymph that contains?..

Macrophages and lymphocytes (B, T cells) that destroy invaders (nodes in neck, groins, armpits, digestive tract)

Swollen ‘glands’

Macrophages and lymphocytes proliferate in lymph nodes causing swollen appearance

Spleen

The largest organ in the lymphatic system; has red pulp for cleaning blood and stores it for emergencies + white pulp is where immune cells (macrophages/pathogen presenting cells, lymphocytes) scan for germs

Can you live without a spleen? Why?

Yes - infection risk is slightly higher, but functions are compensated for by lymph glands, liver and red bone marrow

Thymus gland

Behind sternum, above heart

Thymus’s hormones thymosin and thymopoietin cause what?..

Maturation of T cells (T-lymphocytes)

Thymus is most active during childhood

Yes

Tonsil functions

Filter food and air entering the throat (full of white blood cells)

Adenoids functions

Filter air and protect the nasal passages (tonsils protect the throat)

Skin is an effective deterrent but how else can pathogens enter body?

Saliva, tears, vomiting, mucus, ear wax, digestive and vaginal acids, urination, defecation and resident bacteria (can outcompete pathogens for nutrients because have larger population)

Non specific system has what defences?

Complement proteins, phagocytic cells (neutrophils, macrophages, eosinophils) that go through phagocytosis

Pus

Tissue fluid, dead phagocytes and microorganisms

Inflammation

Redness = vasodilation from histamines released by mast cells, producing blood flow to the injury area; swelling = interstitial fluid leaking out or histamines making capillaries leaky; heat = increased blood flow/vasodilation of capillaries; pain = pressure of fluid on nerves

Why do histamines get released instead of phagocytes/white blood cells?

Phagocytes are too big to get out of the blood vessels, but when blood vessels get leaky from histamine, phagocytes migrate out of them and engulf bacteria

Non-specific characteristics?

Immune cells, chemicals, proteins, fever

Non-specific defenses?

Natural killer cells (lymphocyte that attack viruses, tumor and virus-infected cells by changing proteins on cells membrane), interferons (antiviral proteins/cytokines to destruct viral cells), pyrogens (fever response/raised body temperature to kill pathogens produced by macrophages)

Specific defense mechanisms?

Targets specific pathogens and foreign substances; has “memory” of initial exposure, responding more quickly and aggressively on subsequent exposures; able to distinguish between “self” and non-self invaders OR healthy cells/antibodies/self antigens and abnormal (tumours) cells

Antigen definition

Any substance, usually a protein or specific antibody, triggering an immune response

What cell has major histocompatibility complex proteins?

Self antigens that are on human surfaces, enabling recognition of “self” from “non-self” invaders

Specific antibodies attach to specific antigens (each cell has a unique MHC protein)

Yes (transplants fail if MHC is too different)

B lymphocytes

Antibody-mediated immunity (don’t directly attack foreign cells, but antibodies mark pathogens/antigens for destruction by other immune cells e.g T lymphocytes)

T lymphocytes

Cell-mediated immunity (directly attack foreign, cancerous, or infected cells)

B cells are made in bone marrow, travel to lymphatic tissue, migrate in lymph nodes and spleen (white pulp)- but can become what?

Plasma (release antibodies into blood) and memory cells (stay in body and recognise antigens more quickly than first time)

How do antibodies inactivate pathogens?

Plasma cells secrete antibodies, which bind to antigens (antigen-antibody complex), making pathogens clump together or marking the complex for destruction by phagocytes or complement proteins

2 types of T cells that originate in stem cells within the bone marrow and mature in the thymus are what?

CD4 (helper and memory) and CD8 cells (cytotoxic and suppressor)

How do Macrophages and B cells activate T cells?

Antigen-presenting cells/Macrophages/B cells (APC’s) must show pieces of pathogens to T cells to activate them.

CD4+ T cells turn into helper T cells when activated, making replicates of themselves to identify antigens, and producing cytokines to activate other immune cells/cytotoxic response, where some helper T cells become memory T cells.

What do Cytotoxic T cells do?

Have CD8+ T cells which are activated by antigen-presenting cells (B cells, Macrophages) that directly kill abnormal or cancerous cells via cytotoxic response/toxic chemicals.

Some cytotoxic T cells become memory T cells.

What happens during the primary immune response?

Lag time of 3-6 days for antibody production (specific B cells), peaks at 10-12 days

What happens during the secondary immune response?

Lag time is hours, peaks in days, much more antibody produced (antibodies last longer, memory cells bind to antigens faster, more effective and last longer too)

Why do we get so many colds?

Over 100 viruses that cause colds and evolve rapidly (rapid transmission, but less virulent)

Tissue rejection

Immune system attacks transplanted organ/tissue - to minimise rejection, must match ABO/other blood group antigens and MHC antigens (75% match is essential). Immunosuppressive drugs help immune system from attacking transplanted organ/tissue.

Inappropriate immune system activity causes?…

Allergies = hypersensitive reactions to an allergen (antigen, not a pathogen but body responds as though it is a pathogen)

Inflammation e,g pollen mounting defense = swelling, warmth, vasodilation, mucus influx

Reactions to allergens may be localised or systemic

Localised = only affect the area exposed; systemic = affect several organ systems

Anaphylactic shock = life-threatening systemic reaction (difficulty breathing, circulatory collapse, drop in blood pressure)

Autoimmune disorders can arise from problems with the immune system e.g Lupus and Rheumatoid arthritis

Can’t distinguish self from non-self invaders = autoantibodies (attack healthy cells, leading to inflammation and damage to the immune system) and cytotoxic T cells target the body’s own tissues