immune system Flashcards
why do we need an immune system system ?
. an immune system is essential since we are constantly exposed to harmful microorganisms ( pathogens )
. pathogens vary in size and are constantly evolving
what does the immune system use to protect the body ?
the immune system uses a complex series of protective mechanisms ( cells, tissues and organs ) to control and eliminate these organisms
how does the immune system differentiate between the bodies own cells and foreign cells ?
. this is achieved through self marker molecules , known as major histocompatibility complex ( MHC ) associated with the surface of our own body
. therefore when the immune system encounters cells or organisms carrying foreign molecules it mounts an attack
what is antigen ?
. anything that triggers an immune response is called an antigen , which can be a microbe , part of a microbe or foreign cells or tissues
. e.g. if PX is giver the wrong blood type , the donor red cells , become foreign cells and are attacked
what are the variety of sizes that pathogens can have ?
. viruses : 10 to 1000 nm
. bacteria : 0.1 to 5 micrometers
. protozoa : 5 to 200 micrometer
. fungi : 3 micrometers to > 1 millimeter
what are different infectious diseases of the eye ?
. stye - bacterial infection of the small glands associated with eyelash follicles
. bacterial infection of the cornea - bacterial keratitis
. viral infection caused by virus called herpes simplex keratitis - same virus that causes cold sores
. infective conjunctivitis - which can be caused by a varity of pathogens mostly commonly bacteria and viruses
. acanthamoeba keratitis - protozoan infection of cornea - affects people wearing contact lenses
what are the different lifestyles of microbes ?
. viruses - intercellular infection - need to infect body cells for infection to hold ( also extracellular )
. bacteria - largely extra cellular ( some exceptions )
. protozoa - intercellular and extracellular
. fungi - extracellular
. immune system must deal with both intercellular and extracellular pathogens
what are the two overlapping compartments of the immune system ?
- innate system - first line of defence consisting of a series of physical barriers to prevent entry of pathogens , phagocytes to digest microorganism and chemical mediators to trigger recruitment and activation of immune cells which is referred to as inflammation
- adaptive system - is formed principally by lymphocytes ( T and B cells ) which contain specific receptors to recognise specific antigens associated with pathogens . also retains memory of previous encounter with the pathogen
explain the overview of the immune system ?
- innate system which consists of external defences and internal defences
- adaptive system which consists of antibody mediation - predominantly the role of B - lymphocytes and cell mediation - predominantly the role T - lymphocytes
what is the simplest way to avoid an infection ?
the simplest way to avoid infection is to prevent microorganism from gaining access to the body
what are the components of the first anatomical barrier ?
. the skin is an important barrier and is impermeable to most infectious agents
- intact skin is very good barrier
- cut in skin represents a portal in which microorganism can enter
. the skin also contains glands that produce acidic secretion inhibit bacterial growth due to low PH
- desquamation of skin cells removes potential pathogens
what are internal surfaces that are barriers to infection ?
. mucosal membrane - mucus secreted by membranes lining the inner surfaces of the body block the attachment of microbes to epithelial cells
. washing action of tears and urine also limit attachment
. many secreted fluids contain antibacterial components e.g. acid in stomach , lysozyme in tears and saliva
body fluids are usually antibacterial
what is mucus and what are some examples ?
. glycoprotein produced by goblet cells
. e.g. conjunctiva of eye , oral mucous , constantly washing of fluids over surface thus limiting attachment of microorganisms
what are non-pathogenic microorganisms ?
-non specific (inate) barriers to infection
. many non-pathogenic microorganism are present in the external and internal surfaces of the body where they compete for essential nutrients ( commensals
e.g yoghurt - compete with pathogens - probiotic yoghurt- contain live bacteria- replenish communal orgsanisms in gut and create a healthier environment in gut
what commensals ?
. healthy bacteria - compete in the gut with pathogens
. create much more healthy environment in gut
e.g yoghurt - compete with pathogens - probiotic yoghurt- contain live bacteria- replenish communal orgsanisms in gut and create a healthier environment in gut
what is the internal innate defense mechanism ?
. phagocytosis - phagocyte
- if microorganism penetrate the body can be destroyed by phagocytosis
- phagocytes include the polymorphonuclear neutrophils and macrophages
what are neutrophils ?
- neutrophils are the predominant which cell in the blood stream but can migrate into tissues during inflammation
what are macrophages ?
. macrophages differentiated from blood monocytes
. two types of macrophages mobile( able to move ) and fixed microphages
. mature macrophages settle in tissues where they are strategically places to intercept microbes - fixed
e.g. glial cells of retina in CNS, in run
. phagocytes bind to microorganisms , internalise and kill them
explain the process of phagocytosis ?
. phagocytes arrive at the site of inflammation by chemotaxis
. phagocytes attach to microorganism ( and other targets ) via surface receptors
-Pathogen engulfed by receptors on neutrophils
. microorganisms are then internalised ( phagosome - vacuole within cytoplasm) and destroyed by ( phagolysosome- where micro-organism is broken down )
summary of process of phagocytosis ?
. macrophages / neutrophils have receptors on surface for particular pathogen , then bind to pathogen , then engulf pathogen forming phagosome - a vacuole with cytoplasm , lysosomes then fuse with the phagosome to form phagolysosome
What is the role of a complement system?
. complement system comprises over 30 plasma and cell associated proteins which play an important role in the defence against pathogens particularly against bacteria
. activation of complement begins with recognition protein which bind to wide range of structures including pathogens or structures associated with cellular damage/derbis
what is chemical component of the innate system?
. Complement system
. coordinated series of enzyme - catalysed reaction which provide a series of functions including the recruitment of phagocytes to sight of infection / injury
what does complement system activation lead to ?
complement activation leads to a coordinates cascade of enzymatic cleavage events generating complement protein fragments that carry out particular functions
what are the functions of complement system ?
. recruit phagocytes
. enhance phagocytosis ( opsonisation )
. membrane damage to foreign cells or microbes
what are natural killer cells ?
- they are the final component of innate system
- small fractions ( 2% ) of the lymphocytes circulating in the blood are neither T cells or B cells
- these are called natural killer cells because they are specialised to kill certain types of target cells
e.g. viral infected cells and tumour cells
. able to recognise own body cells through receptors on surface - inhibitory surfaces
. when N-K cells are able to bind to self molecules , it recognises cell as normal cell
. if self molecule is missing labels that service target will get destroyed
why do we have the adaptive system as well as the innate system ?
. microorganisms develop strategies to evade our innate defence mechanisms
. the body has devised defence mechanisms which are tailored to deal with specific microbes
. these mechanisms have both specificity and memory
what is the adaptive system primarily provided by ?
the cellular basis of specific immunity is provided by lymphocytes
where do lymphocytes originate from ?
all lymphocytes originate from stem cells in bone marrow called lymphoid stem cells
what are the two types of lymphocytes ?
. B cells - development occurs within the bone marrow - in some marrow lymphocytes develop into B cells
. T cells - leave the bone marrow develop in the thymus- thymus lymphocytes develop into T cells
what are examples of primary lymphoid tissues ?
. both the bone marrow and thymus are examples of primary lymphoid tissues that are concerned with maturation and development of lymphocytes
what do the bone marrow and thymus do ?
the bone marrow and thymus constitute primary lymphoid tissues where T and B cells differentiate into mature antigen recognising cells
what are secondary lymphoid tissues ?
secondary lymphoid tissues are those in which lymphocyte activation , proliferation and differentiation occurs
e.g. lymph node , appendix, adenoid, tonsil
how do lymphocytes recognise pathogens ?
. lymphocytes are responsible for recognising molecules of infecting pathogens ( antigens )
. lymphocytes have antigen receptors which recognise particular pathogens
what are B cells concerned with ?
.B cells are concerned with the control of extracellular infections
. B cells use cell surface antibodies as antigen receptors
. each antibody molecule has two antigen receptors and antigen receptor is able to recognise a particular type of antigen
. each B cell molecule can only recognise one antigen
what are T cells concerned with ?
T cells are concerned with intracellular infections
. T cells recognise antigens when they are presented to the receptor via MHC molecules
. each T cell can only recognise one particular antigen
what is antigen ?
antigen is anything capable of activating the immune system
what does a large lymphocyte population ensure ?
a large lymphocyte population ensures that an enormous range of antigens can be recognised by the body
what does the immune system do following the first contact with pathogen ?
.following first contact with pathogen the immune system must expand the number of cells which recognise that pathogen
. following recognition of the pathogen the immune system must mount/ increase number of lymphocytes an appropriate response to eliminate it and minimise the damage it causes - cell division causes to increase number of lymphocytes which then differentiate into effector cells - which do the work.
what is clonal section ?
. process of selection of the appropriate lymphocyte
what is the function of memory cells ?
memory cells confer lasting immunity to the particular pathogen
what are the 2 B cells response to antigen recognition ?
1-. antibody response which is mediated through B lymphocytes so when B cells recognise an antigen through antibody receptor on their cell surface , it transforms into antibody-producing cells ( plasma cells )
.2- proportion of activated B cells become memory cells that provide this enhance response such that the second response occurs rapidly
.
why is there delay in antibody production following that initial primary antigen ?
the immune system is undergoing the clonal section , its identified the appropriate lymphocyte ,then there must be that cell division process that supplies a sufficient amount of B lymphocytes in order to get detectable levels of antibody .
. then we begin to get an initial antibody response through a particular subtype of antibody known as IGM , that’s followed by a secondary antibody response which is mediated by another antibody subtype known as IGG, when infection tails away the antibody also falls down .
. secondary antibody response has much shorter latency
what is the antibody structure ?
. antibodies are tetrameric polypeptide structures
. 4 polypeptide chains - linked by disulfide bonds
. there is a region within the amino acid composition that is highly variable
. comprise 2 identical heavy chains and 2 identical light chains
. variable and constant domains
. the variable region- binding region ( termed FAB ) - where antibody recognises antigen
. variation in amino acid composition is to allow the variety of shapes of antigen binding site to encounter different shapes of antigen
. constant region ( Fc) component interacts with cell surface receptors and activates complement pathway-
what are the 5 classes of antibodies ?
ig - immunoglobulin
. igG .IgA .IgM - 5 subunit .IgD .IgE
larger antibody molecules particularly IgM is composed of whole series of antibody sub units
what are the 4 principle functions of antibodies ?
- bind directly to pathogens preventing them from entering or damaging healthy body cells- important in defence against viruses -
- neutralise bacterial toxins- chemicals produced by bacterial cells
- activate complement
- facilitate phagocytosis by opsonization
what is the T response ?
. T cells are responsible for cell-mediated immunity
.T cells include cytotoxic T cells and T helper cells which secrete cytokines ( chemical messengers )
. the T cell response consists of :
. antigen recognition
. activation signals - signals are predominantly coming from T helper cell
. cell division
what is the process of antigen recognition be T cells ?
. T cells recognise antigens as peptide fragments which have come from inside cells
. cells present antigenic fragments ( peptide from cytoplasm ) on their surfaces for review by T-cells
. protein coded by a gene locus known as the MHC are involved in this process
. T cell is making decision about wether that particular pigment peptide fragment is part of normal body
explain the contrast between the innate and adaptive components of immune system ?
INNATE
- rapid response
- anatomic barriers, phagocytes, chemical mediators
- non-specific
- no memory of previous encounter
ADAPTIVE
- slow response
- consists of B and T lymphocytes
- highly specific
- memory of previous immune response and maturation of response
what is immunodeficiency ?
. immunodeficiency - can be congenital , so certain components of immune system may not develop - person is prone to infection
. can also be acquired
e.g. AIDS
what happens when you have hyper reactive immune system ?
. immune system can be hyper reactive so immune system is very powerful
e.g. autoimmunity - immune system recognises self molecules as foreign and triggers destruction
. this can be a systemic autoimmune problem affecting lot of organ or organ specific e.g. autoimmunity within the thyroid gland which leads to reduction of thyroid hormones
what balance do we have in the immune system
. immune system must not be overly reactive but also must have sufficient reactivity to deal with pathogen
What are examples of fixed macrophages ?
microglia cells in CNS (brain and retina )
- lungs- alveolar macrophages
- liver- Kupffer cells
