CASE 5 Flashcards
describe B cells
- form and mature in bone marrow
- then move to lymphatic system to circulate in the body
- pre-programmed to respond to a particular antigen
- the antigen and cytokines (produced by T-helper cells) stimulate the B cells to divide
what happens when a naive B cell encounters an antigen that fits?
it quickly differentiates into either a memory cell or effector B cell (plasma cell)
what do plasma cells do?
secrete monoclonal antibodies
describe T cells
- form in bone marrow and mature in the thymus
- do not make antibodies
- have markers on their surfaces (antigens) called CD antigens (express CD8 or CD4, not both). all have CD3
- populate the lymph nodes, MALT and spleen
when do T cells start to express the CD markers?
during maturation in the thymus
T cells can only recognise antigens that are bound to MHC1 and MHC2. what are these MHC molecules?
they are membrane-bound surface receptors on antigen-presenting cells
what are the 3 types of T cell and what CD antigens do they express?
- cytotoxic T cells (killer cells) - CD8 antigens.
- destroy their targets by releasing perforin - helper T cells - CD4 antigens.
- regulate immune responses by releasing cytokines - suppressor T cells - CD8 antigens.
- down regulate both humoral and cell-mediated immune responses
how does perforin, released by Tc cells, work?
perforin inserts into the lipid bilayer of the target cell and polymerises into a large membrane channel, permeabilising the cell — kills cell
name 2 primary lymphoid organs
bone marrow and thymus
what develops into a macrophage if stimulated?
monocytes
what are neutrophils?
- phagocytic cell
- most abundant and motile WBC
- 1st to reach the site of infection, involved in inflammation
- known as polymorphs - can have 2/3/4 lobes of genetic material
- primary granules contain lysosomes
- secondary granules contain lysosomes that break down bacterial cell walls and lactoferrin (iron-binding protein)
- attracted by leukotrienes
- less effective than other phagocytes but are produced in very large quantities
- produce adhesion molecules in response to IL-1 and TNFa
- secrete chemical mediators that attract macrophages before they die (die once they have phagocytosed a pathogen)
name 3 types of phagocytes
macrophage, neutrophil, dendritic cell
describe dendritic cells
- Langerhans cells in the skin and mucosa
- also found in lymph nodes
- antigen-presenting cells
- in skin-infections, the Langerhan cells engulf the pathogens, presenting the antigens on its surface
- then travel to lymph nodes where they activate CD4 cells (T Helper cells)
describe natural killer cells
- cytotoxic lymphocytes
- less selective than other lymphocytes
- produce perforins, causing interstitial fluid to enter the bacterial cell
- produce granzymes that induce apoptosis in target cell
- activated more quickly than T and B lymphocytes
- activated by cytokines
- cell itself remains unharmed so can go onto kill other cells
name the 5 stages of infection
- entry into body (infection)
- replication and spread
- disease
- exit from the body (infect others)
- reinfecton
intracellular vs extra cellular pathogens
intracellular = spread by cell to cell contact
extracellular = spread by lymphatics and the blood stream
what is the innate immune response?
= pre-existing immunity, doesn’t amplify with repeated attacks by the same pathogen, no memory, non-specific
- physical barriers (skin, resp tract, GI tract, eyes)
- antimicrobial and pro-inflammatory factors
- phagocytes and natural killer cells
- inflammation/fever
what are interferons?
= a cytokine
- released by activated macrophages and lymphocytes and virally affected cells.
- act internally in these cells and they also bind to receptors on normal cells, causing them to produce antiviral proteins. these proteins interfere with viral replication inside the cell
what is lactoferrin?
= an iron-binding protein
- binds to iron
- this removes essential substrate required for bacterial growth
what are TLRs?
= toll-like receptors
- recognise pathogen associated molecules
- around 11 found in humans
- give recognition potential to cells of the innate immune system
eg. TLR5 binds to flagellin
TLR4 binds to lipopolysaccharide from bacterial cell wall
phagocytes
- ‘eating cells’
- monocytes in blood that develop into macrophages in tissue
- neutrophils in blood — less effective but produced in v. large quantities. granules contain toxic substances. live for about 5 days in blood and get attracted to tissue where they eat a couple bacteria and turn into pus
what is pus?
= death of phagocytes
= a collection of alive/dead/dying microbes/phagocytes/local tissue cells
how do natural killer cells work?
= large, granular lymphocytes that are activated by cytokines
- recognise virally infected cells using various receptors
- kill virally infected cell by apoptosis using perforin and granzymes
- NK cell itself is unharmed so it can go on to kill other cells
what are 4 symptoms present at the site of infection?
- redness
- swelling
- heat
- pain
what are the 6 stages of inflammation?
- secretion of chemical mediators of inflammation
- vasodilation
- increased vascular permeability
- activation of adhesion molecules
- chemotaxis
- recruitment of macrophages
name the chemical mediators of inflammation (CMOI)
- prostaglandins - causes vasodilation
- histamine - cause vasodilation, increase vascular permeability
- platelet activating factor (PAF) - increase vascular permeability
- cytokines - secreted by certain cells of the immune system and have an effect on other cells
- IL-1 — causes production of adhesion molecules
- IL-1B — induces fever
- TNFa — causes production of adhesion molecules, induces fever
- leukotrienes — attracts neutrophils from blood stream
- IL-8 — attracts neutrophils to site of inflammation once the neutrophils have entered the tissue from the blood stream
what are the stages of CMOI?
- macrophages (in dermis) secrete prostaglandins, PAF, and cytokines (IL-1, IL-8, leukotrienes, TNFa)
- tissue mast cells and damaged tissue cells secrete histamine, prostaglandins, PAF and cytokines (IL-1/8/1B, leukotrienes, TNFa)
- leukotrienes attract neutrophils to injury site
- the other CMOI have 5 effects:
- vasodilation
- increase vascular permeability
- activation of adhesion molecules
- chemotaxjs
- fever
describe vasodilation
- due to secretion of histamine and prostaglandins
- these bind to receptors on capillaries, causing them to dilate
- increase blood flow to site of injury — area of injury becomes red and hot
describe increased vascular permeability
- due to secretion of histamine and PAF
- these bind to receptors on endothelial cells of capillaries
- causes endothelial cells to shrink — forms interendothelial gaps
- allows protein rich fluid (exudate) to leak from capillaries to the site of injury
- causes swelling
what causes erythema (redness)?
RBCs may also leak through
describe activation of adhesion molecules
- due to secretion of IL-1 + TNFa
- these have 2 effects: 1. cause production/activation of adhesion molecules on the endothelial cells so that they may attract neutrophils from the blood stream. 2. cause neutrophils in the blood stream to produce adhesion molecules so that they may ‘adhere’ to endothelial cells (which already possess adhesion molecules)
name 2 types of adhesion molecules
- selectins
2. integrins
describe selectins
- develop 1st on endothelial cells
- ‘select’ for neutrophils in the blood
- circulating neutrophils have complementary receptors to selectins
- neutrophil loosely binds to selectins and rolls along the endothelial lining
describe integrins
- develop 2nd on the neutrophils
- ‘integrate’ with the endothelial lining
- the endothelial cells have complementary receptors to integrins
- endothelial cells bind strongly with the neutrophils and cause the neutrophils to stop rolling
- causes the endothelial lining to be coated with neutrophils — pavementation
describe chemotaxis
- after pavementation, neutrophils pass through the interendothelial gaps = extravasation
- neutrophils produce collagenases that break down the basement membrane of the capillary
- neutrophils now enter site of injury
- CHEMOTAXIS = THE DIRECTIONAL MOVEMENT OF WBCS DETERMINED BY THE CONCENTRATION OF CHEMOTACTIC AGENTS (IL-8)
- the conc of IL-8 is highest at the site of the injury
- causes WBCs to move towards the centre of the site of the injury
what occurs at the site of the injury?
neutrophils phagocytise the pathogens
- pathogen becomes coated with the antibody IgG and eventually C3b
- neutrophils have complementary receptors to both of these
- pathogen phagocytosis by either direct or indirect opsonisation
- neutrophils engulf the pathogen — forms phagosome
- phagosome binds to lysosome — forms phagolysosome
- the pathogen killed and its contents are secreted
what happens to the neutrophil once is has phagocytosis the pathogen?
it dies
describe the recruitment of macrophages
- before the neutrophils die, they secrete chemical mediators that attract macrophages (stronger phagocytes) to the site of injury
- monocytes (in bloodstream) differentiate into macrophages in tissue
what do macrophages secrete?
prostaglandins, PAF, cytokines (IL-1/8, TNFa)
what triggers a fever and what are its effects?
- triggered by IL-1B + TNFa
- act on hypothalamus (where thermostat is)
- these increase body temperature — inhibits bacterial growth and speeds up certain metabolic reactions and immune system eg. phagocytosis and antibody production
what 3 characteristics does the adaptive immune system have that the innate system doesn’t?
- specificity
- memory
- discrimination between self and non-self
what is the adaptive immune system split into?
humoral immunity and cell-mediated immunity
what are the 4 stages of adaptive immunity?
- inflammation
- phagocytosis
- Th- cell activation and clonal expansion
- B lymphocyte activation, clonal expansion and differentiation into plasma cells
what is humoral immunity?
= antibody or immunoglobulin mediated immunity
- MHC class 2 proteins
- B cells differentiate into memory cells and effector cells (plasma cells)
A LEVEL HUMORAL RESPONSE
- macrophage presents antigens to B cell
- the surface antigens of an invading pathogen are taken up by a B cell
- the B cell’s specific complementary receptors bind to the antigens
- B cell engulfs and digests the antigen
- B cell divides by mitosis — clones form (clonal expansion)
- some of the clones differentiate into memory cells but most differentiate into plasma cells
- plasma cells make and secrete antibodies
describe the structure of an antibody (regular IgG antibody)
- 4 peptide chains
- 2 heavy chains, 2 light chains
- 1 constant region (Fc), 2 variable regions (Fab - antibody binding fragment)
- disulphide bridges join peptide chains
- hinge region joins L and H chains
what is agglutination?
antibodies cause microbes to stick together, making it easier for the phagocytes to idenitfy and engulf pathogens
different heavy chain = different functions. name 5 different heavy chains and their functions
- IgG = blood and tissue antibody, monomer, standard antibody, transplacental transfer, fixes complement, binds phagocytes, neutralises toxins
- IgM = blood antibody, pentimer, acts as a B cell receptor, fixes complement, produced 1st
- IgA = secretory antibody, 2 x IgG, protection at mucosal surfaces
- IgE = binds to mast cells and basophils, important in multicellular parasite infections
- IgD = membrane receptor
how do antibodies protect against infection? — 3 ways
- block binding of pathogens and toxins (antibody binds to the bacterial toxins, forming immune complexes. these complexes are ingested by phagocytes)
- facilitate phagocytosis
- kill bacteria by activating complement
what is opsonisation?
the coating of bacteria by antibody — antibodies/opsonises coat the bacteria so it is targeted for phagocytosis by macrophages and neutrophils, then destroyed inside the cell
what is a slime layer
- bacteria capsule = a polysaccharide capsule outside cell wall
- can be cause of various diseases, found in gram positive and negative bacteria
- when the secretion that makes up the capsule diffuses into the surrounding medium and remains a loose, demarcated secretion = slime layer
what is the importance of a slime layer?
- a virulent factor as it enhances ability of bacteria to cause disease eg. prevents phagocytosis and engulfment by macrophages
- a capsule-specific antibody may be required for phagocytosis
what is the result of a severe block in B cell development?
hypogammaglobinaemia (low antibody in blood — immunodeficiency)
what MHC proteins are used in cell-mediated immunity?
MHC class 1 proteins