third line of defence

features of the third line of defence (3)

specific response

targets specific pathogens

stores memory

B cell purpose summary

produce specific proteins called antibodies that are produced against specific antigens

T cell purpose summary

target pathogens directly

leukocyte type of molecule

pattern recognition molecule

TLR

-Toll-like receptors

what do TLRs recognise

microbial molecules called pathogens-associate molecular patterns

PAMPs

pathogens associate molecular patterns

property of PAMPs

non specific - common to a range of pathogens

humoral response simple (2)

involves actions of B-cells to produce antibodies

antibodies, complement proteins and antimicrobial peptides floating in serum / lymphatic and extra cellular fluids

cell mediated response simple

involves production of specialised lymphocytes (T cells)

two varieties of third line of defence

humoral response

cell mediated response

how do the varieties of third line of defence interact

both systems work separately and together

where are lymphocytes produced

in the bone marrow

where do the lymphocytes mature

B cells in the bone marrow

T cells in the thymus gland

what is an antibody

an immunoglobulin that is a protein made in response to antigens

properties of an antibody (3)

antibodies recognise and bind to antigens

antibodies are highly specific and can help destroy antigens

each antibody has at least two sites that can bind to an antigen

antibody structure (5)

antigen binding site is specific (variable region)

-> one on each arm, two per antibody

-> complimentary shape to only one antigen

2 light chains (polypeptides)

2 heavy chains (polypeptides)

hinges allow for bending

disulphide bridges

FAB

fragment antigen binding region

fragment antigen binding region

variable regions

bind to and recognise speciifc antigens

FC

fragment crystallisation

fragment crystallisation

constant regions

interacts with cell surface receptors and complement system to trigger response

immunoglobulin definition

A term for all antibody molecules.

immunoglobulin types (5)

IgG

IgA

IgM

IgE

IgD

IgM

antibodies usually the first to be secreted that cause agglutination of antigens, making it easier for phagocytes to conduct phagocytosis

agglutination definition

Clumping of foreign cells; induced by crosslinking of antigen-antibody complexes.

IgG

activate complement proteins, neutralise toxins directly

IgA

neutralise pathogens in the digestive, respiratory and reproductive tracts

IgE

help initiate inflammation

IgD

function unknown

neutralization

antibodies bind to viral binding sites and coat bacterial toxins

precipitation of soluble antigens

soluble antigens are stuck together to form precipitates

what do neutralisation, agglutination and precipitation of soluble antigens enhance

phagocytosis

what do activated complement proteins enhance (2)

enhances phagocytosis

enhances inflammation

what do activated complement proteins lead to

leads to ruptured cell

where do B cells migrate from and to

from bone marrow to lymphatic organs

what do B cells defend against (2)

bacteria and viruses outside the cell

toxins produced by bacteria (free antigen)

how many different types of antibodies can a B cell produce

only one type against one specific antigen

how many antibodies can a mature B cell carry

thousands, embedded into surface membrane

why is having a small number of each antibody type a good thing

higher chance of recognising the antigen

humoral response complex steps (3)

1. humoral response begins when a foreign protein (antigen) activates a particular B cell

2. the particular B cells multiply to form many plasma cells

-> CLONAL EXPANSION

- plasma cells make antibodies specifically designed to attack and kill the identified pathogen

3. some B cells differentiate into long lived memory cells

these memory cells will rapidly produce antibodies if the same pathogen enters the body again

B cell differentiation (2)

•Memory B cells

•Remain in the body to provide long term immunity

Plasma B cells

•Produce antibodies

memory cells (long lived)

when these encounter the same antigens again (even years or decades after the initial infection), they rapidly differentiate into antibody producing plasma cells

plasma cells (short lived)

these secrete antibodies against antigens

each plasma cell lives for only a few days but can produce about 2000 antibody molecules per second

Naive B cells

B cells that have not been activated via cytokines from T helper cells yet

when does clonal selection occur

after phagocytosis of a foreign agent

clonal selection steps (3)

antigens are presented on macrophages / dendritic cells on MHC II markers

these cells migrate to the lymphnode

they meet with the naive B cells until the antigen 'selects' one with a complimentary antibody

when does clonal expansion occur

after the antigen has attached to an antibody / immunoglobulin

clonal expansion

antigen presentation to the T helper cell

the T cell receptors on the T helper cell recognise and bind to the selected B cell (also displaying the antigen on its MHC2 marker) and bind to this complex

T helper cell releases cytokines (chemical messenger) that active the B cell

the selected B cell needs to reproduce rapidly so that there are many identical cells that can respond to the antigen

cells cloned this way have the same genetic material and immunoglobulins

most of these cells will then differentiate into plasma cells

where do plasma cells secrete

into bloodstream

how do plasma cells secrete

via exocytosis

what do B memory cells respond to

secondary exposure

features of B memory cell (3)

faster

larger

longer response

clonal selection and expansion steps (5)

1. B cells encounter and bind to antigen

2. B cell (specific one) responds to antigen by proliferating

3. same B cells differentiate into long lived memory cells

4. other B cells differentiate into plasma cells

5. plasma cells secrete antibodies into circulation

T-cells origin and maturity

originate from stem cells and mature after passing through the thymus gland

what do T cells respond to

respond to antigenic fragments that have been processed and presented bound to the MHC markers by infected cells or macrophages (phagocytic cells)

what do T cells defend against (3)

intracellular bacteria and viruses

protozoa, fungi, flatworms, round worms

cancerous cells and transplanted foreign tissue

how many different cells can a T cell differentiate into

4

types of cells T cell differentiates into (4)

helper T cell

Suppressor T cell

T cell for delayed hypersensitivity

cytotoxic (killer) T cell

helper T cell (2)

activates cytotoxic T cells and other helper T cells

necessary for B cell activation

suppressor T cell

regulates immune response by turning it off when no more antigen is present

T cell for delayed hypersensitivity

causes inflammation in allergic reactions and rejection of tissue transplants

cytotoxic T cell

destroys target cells on contact

cell mediated immunity steps (3)

1. antigens, such as those produced by abnormal cells are identified by the specific killer T cells

2. with the assistance of helper T cells, the killer T cells being to multiply

3. The killer T cells attach to and destroy the abnormal cell. killer T cells remain as memory cells to quickly attack any abnormal cells that reappear