BIOL 273 - Unit 6.3 Flashcards
Basic steps of immune response (regardless of foreign substance)
- Detection and identification of foreign substance
- Communication with other immune cells
- Recruitment of help and co-ordination of the response
- Destruction or suppression of the invader
What kinds of chemical signalling does the immune response use
Antibodies (Ab) - bind to antigen as a signal
Cytokines - affect growth or activity of other cells
What are the two main categories of immunity
innate and adaptive immunity
- overlap and cooperate in mounting responses to pathogens
Describe the response time of innate immunity
Innate - more rapid , less specific response - can lead to adaptive
Describe the response time of adaptive immunity
response is slower, more specific
Describe innate immunity
present before pathogen is encountered and is non-specific
response begins within minutes to hours, and it does not remember past infections
some non-specifc cell types and proteins
inflammation is distinctive in innate immune response
Present in all organisms
Describe adaptive immunity
directed at specific invaders (aka acquired immunity)
Develops after the pathogen is encountered and the response takes days to weeks
Remembers past infections
Only found in vertebrates
What can adaptive immunity be further divided into
Cell-mediated immunity
Antibody mediated immunity (humoral immunity)
Line of defences of innate immunity
physical and chemical barriers provide the first line of defence (most vulnerable since exposed to outside)
Second line of defence are patrolling or stationary leukocytes and blood proteins (react same way to every infection)
(provide clearance of pathogens or containment of the pathogen until adaptive response kicks in)
Innate immune system cells
Majority are phagocytes (destroyes/suppress invader ingesting it)
Attract other cells by secreting cytokines which will attract other immune cells via chemotaxins
- cells that are attracted are cytokines, products of tissue injury, bacterial products
Describe how phagocytes engulf invaders during phagocytosis (innate immunity)
Phagocytes leave the circulation and enter tissue through capillary walls (aka extravasion)
They identify the invader by chemical cues which interacts with receptors on the phagocyte membrane
Many receptors bind sequentially to allow the phagocyte to engulf the invader
Movement of pseudopodia via actin filaments push the cell around invader
What happens in phagocytosis when pathogens do not have surface features that can be recognized directly by phagocyte (innate immunity)
blood proteins bind to and coat the pathogen to “tag” it
Phagocytes have receptors for these blood proteins
“Tagging” a pathogen is called opsonization
A protein that can do it is an opsonin
Phagocytosis: what happens once the pathogen is ingested
the particle is in a vesicle called a phagosome
These fuse with lysosomes which contain digestive enzymes and chemicals that kill the pathogen
- forms a phagolysosome
Pus
Dead phagocytes, tissue fluids and debris collected at the site of injury
Those phagocytes that are also APCs present antigens from digested bacteria on the surface of the APC via class II MHC
Natural killer cells
lymphocytes associated with innate immunity
- kills an infected cell that is not presented with MHC I
- do not have specific receptors as seen in B cells and T cells
- They bring out apoptosis in pathogen-infected cell
- Can also attack tumour cells
What do natural killer cells produce
cytokines such as interferons ; interfere with viral replication
- IFN alpha and beta - induces an “antiviral state” in nearby cells that prevents viral replication
- IFN gamma - activates macrophages and other immune cells
Role of chemical mediators
- play a role in the innate response
- create the inflammatory response - red warm swelling in skin is hallmark of innate response
- caused by cytokines that are released by macrophages
Describe the purpose of inflammatory response of chemical mediators
- serves as a signal to attract other cells and chemical agents to the site
- Increase capillary permeability and causes fever
- A physical barrier is produced - prevent the spread of pathogen
- tissue repair is promoted
Interleukin 1 (IL-1)
produced by cells within innate immune system such as macrophages - mediates effects of inflammatory response of chemical mediators
- act on endothelial cells lining the blood vessels - loosens junctions between cells
- act on liver cells to produce blood proteins involved in damage control
- Induce fever
- Stimulate cytokine production
Complement proteins
- take part in innate response (blood proteins)
- activated by sequential proteolysis
- some are opsonins, some are chemotaxins , some form membrane attack complex and make holes in pathogen membranes
Describe the Membrane Attack complex
Use of complement proteins in innate response:
- results in “MAC Attack”
C1 binds to an anitogen antibody complex on an invading pathogen, causing complement components to split in two
proteins continue to split util C3a attracts phagocytes to infection site
fragments joins to form membrane attack complex, which makes a hole in the pathogen’s plasma membrane, water rushed into the hyperosmotic cytoplasm, causing the pathogen to lyse
What is adaptive immunity started by
products of innate immune response
Adaptive immune system cells
lymphocytes and lymphocyte products
1. Natural killer (which is in innate response)
2. B cells (activated form = plasma cell)
3. T cells (Tc and Th and Tregs)
clone
a population of lymphocytes that has a specificty towards one particular antigen
Features of lymphocytes of adaptive immune response
- T cells and B cells can be expanded clonally
- each individual cell recognises a different specific pathogen - known as specificity
- few naive cells (never encountered specific antigen)
- once they recognize a pathogen - expand clonally - many effector cells
- these effector cells attack the pathogen to become memory cells
Adaptive immunity; antibody-mediated immunity; what cells take part in this
- B cells produce antibodies that take part in antibody-mediated immunity aka HUMORAL IMMUNITY
Antibodies are proteins that bind specifically and target pathogens for destruction
antibodies of antibody mediate immunity
AKA IMMUNOGLOBULINS
- can be either a cell membrane protein or B lymphocytes or secreted
- membrane Ab’s can be used as markers to identify each different clone of B cells
What do stimulated B cells mature into in antibody-mediated immunity
mature into plasma cells
- essentially antibody factories (producing many antibody molecules per second)
- plasma cells are short lived but few memory cells survive
Primary antibody response
Primary response happens on the first exposure to an antigen
- slower response and less antibody concentration
- delayed response
Secondary antibody response
happens much faster because of mediated memory cells
- more antibodies produced
Why do vaccinations work
patient is given an inactivated or partial pathogen
- they generate memory cells that recognize the natural pathogen (if encountered in the future)
- allow memory cells to clonally expand
Immunoglobulin: IgM
- produced during primary response (battling pathogen for the first time)
- activates complement (MAC attack)
Immunoglobulin: IgA
found in secretions that can interact with specific antigen
neutralize pathogen before entry of body
ex. tears, mucus, salvia
dimer; 2 subunits coming together
Immunoglobulin: IgD
Found on surface of B cells with IgM
function unknown
immunoglobulin: IgG
Majority of antibodies in plasma
Secondary response antibody
activates complement
opsonizes
Immunoglobulin: IgE
allergic response
recognized by mast cells
Antibody structure
- four polypeptides linked into a Y shape with 2 light chains and 2 heavy chains
- each side of the Y is identical (one ligt chain linked to one heavy chain)
- The arms (Fab) contain the antigen binding sites
- The stem (Fc) determines which of the five classes an antibody belongs to
- There is a hinge in between the Fab and Fc portions
antibody function
do not damage pathogen themselves
- instead, they make pathogens more visible to immune defences or activate
- humoral immunity help initiate innate immunity response
- immune cells recognize stems of antibodies (interaction)
seven antibody functions
- Act as opsonins to tag Ag’s for phagocytosis
- Cause antigen/pathogen clumping
- Neutralize bacterial toxins
- Activate complement
- Activate b cells
- Activate Ab dependent cellular activity
- Activates mast cells to degranulate
Adaptive immunity: cell mediated ; what cells are mediate this
- T cells need to be in contact directly with the target cell expressing an antigen
- T cell receptor (antigen specific molecule) is expressed only as a cell-surface protein
- Detects Ag presented on the surface of a target cell via the MHC receptor
- T cell cannot bid to free antigen (must be displayed on class I or class II)
Class I MHC
present on the surface of every nucleated cell in the body
- defend against pathogens that get inside cells
- peptides are presented in MHC class I to cytotoxic T cells (Tc)
- Tc cells kill the cells that express the peptides
- Tc cells can also express the Fas ligand to kill target cell via apoptosis
What do Class I MHC release
perforin - which forms pores in target cell
granzymes - which enter through the pores and trigger apoptosis
Class II MHC
present on the surface of specialized immune system cells - APC’s b
- cells respond to extracellular pathogens
- Phagocytose pathogens - present peptides in MHC class II to Helper T (Th) cells or regulatory T (Treg) cells
- Th cells respond by secreting cytokines that activate other immune system cells
- Treg cells respond by secreting cytokines that suppress other immune system cells
