Chapter 7 Immunity: Lines of defence

innate response

a non specific response against a pathogen

first line of defence

chemical, physical and microbiota barriers that aim to keep the pathogen out.

normal flora

naturally occuring microorganisms that live in or on animals and plants and do not cause harm or an immune response

pathogenic bacteria

bacteria that cause harm and an immune response

inflammatory response

heat, pain, redness, swelling and loss of function as part of the innate immune response to harmful stimuli

Mast cells

granulated cells that release histamine (an amine signalling molecule) which triggers inflammation. They are found in the respiratory tract, the gastrointestinal tract and in deep skin layers.

histamine

compound released by some white blood cells to trigger an inflammatory response

Macrophages

Large phagocytes that become powerful stimulators of the immune system when they engulf a pathogen (due to the non-self antigen).

Cytokines

Powerful immune signalling molecules that attract immune cells to the site of infection or damage.

second line of defence

innate and non-specific

Antigen Presenting Cell (APC)

a specific type of white blood cell that uses phagocytosis to engulf a pathogen before displaying the non-self antigen on its MHC II markers. They are the bridge between the second and third lines of defence

apoptosis

programmed cell death

Natural Killer (NK) cells

Attack cells that are infected with a virus or have become cancerous (they do not respond to pathogens outside of a cell)

Vasodilation

a physiological response triggered by the release of histamine. Results in the widening of the blood vessels allowing greater blood flow through to the affected area for increased action of phagocytes.

lysis

breakdown of the cell membrane

Dendritic cells

Patrolling phagocytic cells that engulf pathogens, then present the antigen of the pathogen to other cells. Act as APCs providing a link between the innate and adaptive immune response.

Neutrophils

Phagocytic cells that rapidly enter sites of inflammation, engulf pathogens and die quickly. Pus contains the debris of dead neutrophils.

Eosinophils

Cells that release powerful enzymes that rupture (lyse) the cell walls of pathogens

Complement proteins

Small proteins found in the blood that when activated facilitate the destruction of pathogens by phagocytosis, attract phagocytes and form pores in pathogen membranes leading to lysis.

Interferons

a type of cytokine secreted by some cells in response to virus infection that help uninfected cells resist infection by that virus.

Basophils

Cells that also secrete chemicals, including histamine. Have been linked to allergic reactions and asthma.

Platelets

component of blood that form clots and stop or prevent bleeding.

lymphocyte

A type of white blood cell; includes B and T lymphocytes

Leukocytes

a general term for white blood cells

adaptive immune response

response of the immune system to a specific antigen which typically results in immunological memory

interstital fluid

Fluid in the spaces between cells. This fluid becomes lymph when it enters lymph capillaries.

lymph

colourless fluid that flows through the lymphatic system

lymphoid organ

organ involved in the production or function of lymphocytes

lymph node (secondary lymphatic organ)

a major site of filtration for the identification of non-self antigens to trigger the adaptive immune response

bone marrow

A soft tissue inside the bone that produces all blood cells (including B and T lymphocytes)

thymus

Gland in the thoracic cavity above the heart where T lymphocytes mature.

immunological memory

the ability of the immune system to quickly and specifically recognise an antigen that the body has previously encountered and initiate a corresponding immune response

clonal selection theory

the scientific theory that a specific antigen activates a specific lymphocyte that has a complementary receptor

naive

not yet activated

antibody

a quartenary protein that has a Y shape containing two identical arms each with an antigen binding site specific to an antigen; also referred to as immunoglobulins (Ig)

clonal expansion

the proliferation of a lymphocyte that has been selected by a complementary antigen

plasma B cells

result of naive B cell activation and produce specific antibodies to a particular antigen that activated the naive B cell.

memory B cells

result of naive B cell activation and remain in lymph tissue for long periods, aiding in providing longer term immunity and a faster, stronger immune response if secondary exposure to the antigen occurs

Agglutination

where antibodies join to the pathogen's antigens, joining more than one pathogen together (clumping)

Helper T cells (Th cells)

with their TCR recognise specific complementary antigen presented to them on the MHC II marker of an APC. Release cytokines and trigger the clonal expansion of Tc cells and memory T cells

Cytotoxic T cells (Tc cells)

directly attack pathogen infected host cells by recognising antigen fragments presented on MHC I of infected host cells. Bind to these cells with their complementary TCR and give the infected cell the 'death signal' triggering the cell to undergo apoptosis

Memory T cell

remain present after the primary infection has been resolved. Assist in long term immunity and generate a faster and stronger response upon subsequent exposure (T cell related)

humoral immune response

The branch of adaptive immunity that involves the activation of B lymphocytes and that leads to the production of antibodies, which defend against extracellular pathogens.

cell mediated response

The branch of adaptive immunity that involves the activation of cytotoxic T cells, which defend against intracellular pathogens.