BIO U4AOS1

IMMUNITY

antigens

a substance that the immune system recognises as foreign, triggering a targeted immune response

self-antigens

marks a cell as ‘self’ so the immune system does not attack it

• located on the surface of cells

non-self antigens

a substance originating outside the body that the immune system identifies as foreign, triggering an immune response

pathogens

microorganisms that cause disease upon entering a host

pathogenic disease

disease caused by a foreign object

autoimmune disease

immune system fails to recognise cells as ‘self’ and attacks body’s own healthy cells and tissues (overactive)

immunodeficiency disease

immune system’s ability to fight infection and disease is compromised (underactive)

bacteria

pathogenic prokaryotes which release toxins making us sick

fungi

eukaryotic organisms mainly causing disease in plants

parasite

organism which lives/feeds off of

viruses

protein or lipid capsules containing nucleic acids

prion

rogue protein that can trigger abnormal folding of similar proteins

first line of defense

prevents apthogens from entering the body, non-specific

physical barriers

barriers that block pathogens from entering the organism

examples of physical barriers

• skin

• mucus

• hair

• waxy cuticles

• stomata closing

chemical barriers

chemical substances that make an environment unstable for the pathogens to exist in

examples of chemical barriers

• stomach acid

• earwax

• lysosomes in tears, sweat, etc

microbiological barrier

gut flora which breaks down nutrients during digestion, but prevent pathogenic bacteria from colonising the gut

second line of defence

immune response when the pathogen has entered the body

leukocytes

white blood cells

MHC-I marker

presented on all nucleated cells of the body: receptor protein that allows cells to be recognised as ‘self’

cell surface receptors

region on the surface of a cell that receives and binds to extracellular molecules → cell signalling

MHC-II markers

presented on white blood cells; Macrophages and dendritic cells present antigens on their surface on the MHC-II markers, which bind to helper T cells to activate the adaptive immune response.

cellular pathogens

disease-causing agents which reproduce independantly

intracellular

within the cell

extracellular

outside the cell e.g. blood plasma, extracellular fluid

allergens

antigen that elicits an allergic response

mast cells

type of leukocyte which releases histamines when surrounding cells are damaged

inflammatory response

• vasodilation

• increased permeability of blood vessels

• attract phagocytes

innate immunity

present from birth; produces non-specific responses

adaptive immunity

specific response to particular antigens → develops through contact with antigens

immunological memory

the ability of the adaptive immune response to remember antigens after primary exposure through memory cells

lymphocytes

a class of leukocytes (white blood cells) which includes B lymphocytes, T lymphocytes, and is found in the lymph nodes

phagocytosis

process where phagocytes consume and destroy foreign or dead material by engulfing it through endocytosis

phagocytes

group of leukocytes responsible for the endocytosis and destruction of pathogens, foreign material, and cell debris

cells involved in the 2nd line of defence

• eosinophil

• mast cell

• neutrophil

• macrophage

• dendritic cell

• natural killer cell

third line of defense

involves the neutralisation and destruction of pathogens via the production and secretion of antibodies

neutrophils

• most abundant leukocyte

• first cells to arrive at the site of infection

• they identify and launch phagocytic attack on microbes

eosinophils

leukocytes which secrete cytokines, defense against larger parasites

basophils

leukocytes which secrete histamine; involved in allergic reactions

natural killer cells

• leukocytes which recognise virus-infected and cancerous cells (cells lacking ‘self’-markers)

• secretes cytotoxic chemicals which punches holes in plasma membranes, triggering apoptosis

macrophages

leukocyte which identifies and eliminates pathogens via phagocytosis

dendritic cells

antigen-presenting cell which secretes cytokines

mast cells

leukocyte that secretes histamine, which dilates blood vessels and promotes inflammation

→ involved in allergic responses

steps of phagocytosis

1. pathogen is identified and is engulfed by the plasma membrane of the phagocyte, and packaged into a vesicle

2. lysosomes fuse with the vesicle

3. toxic chemicals from the lysosome digest and destroy with pathogens

4. indigestible material is discharged from the phagocytic cell and by a process of exocytosis

complement proteins

proteins that circulate in the blood and are able to help kill foreign cells

role of complement proteins

1. Opsonisation: complement proteins stick on the outside pathogens, making immune cells more susceptible to recognise them as foreign

2. Chemotaxis: complement proteins gather near a pathogen and attract phagocytes to it

3. Lysis: complement proteins join together on pathogen surfaces which creates pores on its membrane. This causes fluid to enter the pathogen, causing it to burst

inflammatory response

increases blood flow to an injured area, bringing a greater number of immune cells and components to clear debris and fight potential pathogens

characteristics: swelling, pain, heat, and redness

interferons

cytokines released by infected cells to warn neighbouring cells of infection

→ they signal adjacent cells to:

• inhibit protein synthesis

• destroy RNA

• make the plasma membrane less fluid to make fusion more difficult

• activate immune cells

functions of the lymphatic system

• production and maturation of immune cells

• removal of excess fluid from tissues

• absorption and transportation of fatty acids to the digestive system

• allowing for process of antigen recognition by T and B lymphocytes

lymph

fluid in the lymphatic system that gets squeezed out of blood vessels

primary lymphoid organs

→ Bone marrow: source of stem cells, site of maturation of B cells

→ Thymus: where T cells mature after being released from the bone marrow

secondary lymphoid organs

→ Spleen: filters the blood that passes through it, clearing bacteria, viruses, and blood cells. Contains T and B cells that detect and respond to infectious agents in the blood

→ lymph nodes: site where antigen recognition occurs; antigen presenting cells display their antigens to their specific T and B lymphocytes