Third line of defence Flashcards
what are the characteristics of the adaptive immune response?
It is highly specific: able to recognise and respond exclusively to antigens
immunological memory: cells ‘remember’ antigens after initial exposure, allowing a larger and faster response upon re-exposure
what cells are the adaptive immune response carried by?
white blood cells called B and T lymphocytes
what is the function of B cells in the adaptive immune response?
B cells help perform main role in the humoral immune response. B cells are activated and secrete specific antibodies (immunoglobulins) which circulate in the blood stream and target specific non-self antigens in the extracellular space
What is the function of T cells in the adaptive immune response?
T-cells perform main role in the cell mediated response, targeting host cells infected by pathogens, such as virus. Antigens from the virus is presented to the T-cell and this instruct T cell to induce the virally infected cell to die. This prevents virus replicating and T-cells can also kill cancerous cells or transplanted cells
what is the crossover between innate and adaptive immune systems?
T-cells are activated through cytokine exchange with APCs and naïve B cells are activated by cytokines released by T-helper cells
what is humoral immunity?
occurs in the blood and lymph where antibodies produced by lymphocytes, are secreted onto extracellular fluid. Humoral immunity responds to extracellular pathogens and involves B cells and antibodies.
what is the clonal selection theory in the humoral response?
non-self antigens act as selecting agents and activates correct naïve b cell, initiating humoral immune response
why can adaptive immune response recognise and response to millions of unique non-self antigens in the humoral response?
In the lymph nodes there are millions of naïve b cells with 10^5 unique antibody like receptors and complementary antigen binding sites
what happens when a complementary b cell is selected?
when a corresponding naïve b cell is selected by a non-self antigen, the naïve be cell proliferates, making clones of itself and then the clones differentiate into memory B cells and plasma B cells.
what happens after proliferation and differentiation of B-cells
-Plasma B cells secrete antibodies with the same antigen binding site as original antibody receptor on naïve B cell. Antibodies flood the blood stream and perform their function at infected site
What results in immunological memory of humoral response?
memory B cells have the same antibody surface receptors as naïve b cell but can survive a lot longer than plasma B cells- which leads to long term immunity. If the same pathogen with the same antigens invade, the memory cells in blood stream will recognise it and response will be faster and stronger
characteristics of naïve B-cell
- have receptors similar in structure to antibodies and identify antigens through their Ig like receptors binding to them
- there are specific naïve B cells for specific antigens therefore, different pathogens
characteristics of plasma B cell
- plasma B cells perform main role of humoral immune response
- plasma B cells result from naïve B-cells being activates and undergoing clonal expansion
- produce antibodies against antigen that activated the naïve B-cell
- antibodies are released into the bloodstream
- survive for only a few days
what are a antibodies called and what are they made of?
antibodies are known as immunoglobulins and are made up of proteins
How are antibodies produced?
antibodies are produced by plasma B-cells
characteristics of antibodies
- antibodies target and bind to specific non-self antigens that are in the extracellular space
- They will have the same antigen binding site as the original cell surface receptors on the original naïve B cell
- they can be find bound to the plasma membrane of B lymphocytes or floating freely in extra cellular spaces
what is the structure of antibodies?
- antibody is composed of 4 polypeptide chains: two heavy and two light chains forming a Y-shape. At the end of each arm, there is the same antigen binding site made up of both a heavy and a light chain. - The two chains making up the binding site are known as the variable region.
- the variable region is specific and only matches to one antigen
- the constant region is below the variable region and is the same for all antibodies
- the constant region has functions such as activating complement proteins and binding to phagocytes
- The heavy and the light chains are held together by disulphide bonds
what is an antigen paratope?
it is the antigen binding site on antibodies which is complementary to a specific antibody epitope
what are the benefits of hinge region of antibodies
it increases flexibility and improves efficiency in antigen binding and cross linking during agglutination
what is the function of the variable region on antibodies?
- it has a specific shape to select a specific antigen and allow antibodies to bind to different antigens
- it is the antigen binding site between the antigen and antibody
- the two binding sites are identical to each other on each arm of the Y shape
how do antibodies have such variety?
variable portion of antibodies have relatively small number of genes that are cut and shuffled randomly to produce millions of different combinations. This allows random production of innumerable antibodies
characteristics of the constant region of antibodies?
- the constant region is the same in all antibodies
- aids in recruiting other components of the immune system and acting as binding sites (e.g. binding to pathogens, activating complement proteins)
- It is the single stem of the Y-shaped antibody and is a conserved sequence in all antibodies
what are the five types of antibodies?
DEGMA (IgE, IgG, IgM, IgD, IgA)
- IgG is secreted by the plasma cells and is the main antibody that assists phagocytes (able to cross the placenta and travel to the foetus)
- IgM are produced during primary/first immune response. Attached to B cells and secreted into the blood by plasma cells. The first form of antibody produced by plasma cells in response to an infection
- IgE protects against parasite worms and are responsible for allergic reactions as they are receptors for mast cells
IgA is found in external secretions (such as mucous, breast milk and saliva) and guards the entrances to protect against pathogen invasion
- IgD is located on the surface of B-cells and is important for activation of other immune cells and acts as a receptor to stimulate clonal selection
What is Ig A antibody
IgA is found in external secretions (such as mucous, breast milk and saliva) and guards the entrances to protect against pathogen invasion
What is IgM antibody?
- IgM are produced during primary/first immune response. Attached to B cells and secreted into the blood by plasma cells. The first form of antibody produced by plasma cells in response to an infection
what is the IgG antibody?
- IgG is secreted by the plasma cells and is the main antibody that assists phagocytes (able to cross the placenta and travel to the foetus)
what is the IgE antibody?
- IgE protects against parasite worms and are responsible for allergic reactions as they are receptors
What is IgD antibody
- IgD is located on the surface of B-cells and is important for activation of other immune cells and acts as a receptor to stimulate clonal selection
what are the ways that antibodies interact with pathogens?
- neutralisation
- immobilisation
- agglutination
- opsonisation
- activation of complement proteins
- precipitation
describe the process of agglutination
antibodies can bind together with antigens on two separate pathogen surfaces, forming large antigen-antibody complexes. This process makes it easier for phagocytes to recognise the pathogens as foreign bodies and destroy them. It enhances the ability of phagocytes to engulf more pathogens at once
describe the process of neutralisation
antibodies can block the sites of pathogens that are used to attach host cells (e.g. can block the site used by a virus to enter a cell) and can block the active sites of toxins
describe the process of precipitation
antibodies bind to soluble antigens, causing them to become insoluble and precipitate out of the solution
describe the process of opsonisation
a pathogen tagged by antibodies provides a readily recognisable structure for macrophages or neutrophils and therefore increases phagocytosis
activation of complement proteins by antibodies
binding of compliment proteins to an antigen-antibody complex triggers a cascade in which each protein of the complement system activates the next protein
- ultimately forms a pore in the membrane of the foreign cells and ions and water rush into the cell causing it to lyse
it promotes inflammation and stimulates phagocytosis
how do antibodies facilitate positive feedback?
they facilitate positive feedback between innate and adaptive immune responses that enhance the effectiveness of responses to infection
- phagocytosis enables macrophages, neutrophils and dendritic cells to present and stimulate helper T cells, which in turn stimulate the very B-cells whose antibodies contribute to phagocytosis
what is cell mediated immunity?
it involves T-cells responding to infected cells
characteristics of T-cells
- highly specific to non-self antigens due to presence of their T-cell receptors
- T- cells respond to antigen fragments
- T-cells need to be presented with antigen fragments by APC
- T-cells respond to cells that have been infected
characteristics of naïve T-cells
- have T-cell receptors that recognise specific antigens
- they are unable to recognise antigens without assistance of APCs
characteristics of helper T-cells
- Their TCR will recognise specific complementary antigens presented to them on the MHC II marker of an APC
- after being activated by cytokines released by APC, they undergo clonal expansion, producing effector T-helper and memory T-helper cells
characteristics of effector T-helper cells
Effector T helper cells release cytokines
- cytokines assist activation of cytotoxic t-cells and naive B-cells
- cytokines assist with activating macrophages and promote inflammation at site of infection
characteristics of cytotoxic t-cells
-directly attacks pathogen infected host cells by recognising antigen fragments on MHC I marker of infected host cell
- cells are killed through release of perforin which puncture plasma membrane of the assist, assisting in initiation of apoptosis
characteristics of memory T-cells
- remain present after primary infection has been completed
- assist in long term immunity and generates a faster and stronger response upon secondary reinfection
what are the steps in cell mediated immune response?
- A phagocyte with phagocytose a pathogen as part of the innate immune response. The phagocyte will present a fragment of the phagocytosed pathogen on it MHC II marker, now acting as an APC
- The APC will locate a naïve T-cell with a complementary T cell receptor to the MHC II marker on the APC
- The now activated naïve t-cell proliferates into effector cells called T helper cells and cytotoxic t cells. Memory cells are also produced
- T-helper cells activate macrophages at site of infection to carry out further phagocytosis, initiate the humoral immune response as well as activate cytotoxic T-cells to kill infected host cells
- Cytotoxic T-cells recognise host cells that have been infected by a pathogen through MHC I markers. Once infected host has been identified, the cytotoxic T-cells will release perforin and granzymes to cause lysis and initiate self destruction by the cell.
what are suppressor T-cells
suppressor T-cells regulate immune responses and stops activity when the invader has been defeated. This prevents wastage of resources
How is self tolerance developed?
during development, T-lymphocytes that react to self antigens are normally destroyed. The inability of lymphocytes to respond to self antigens is known as self tolerance.
difference between cytotoxic T-cells and natural killer cells
Cytotoxic T-cells are part of the adaptive immune response and are activated by specific MHC I markers on target cells
Natural Killer cells are part of the innate immune response and are activated by the lack of MHC I markers or damaged MHC I markers on target cells. There is no immunological memory for NK cells
Both of these cells recognise virally infected cells and release cytotoxins perforin (cell lysis) and granzymes (apoptosis)
what are the two cytotoxins mostly used by cytotoxic cells
perforins and granzymes
what does release of perforins cause?
cell lysis
what does the release of granzymes cause?
apoptosis
what is 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
How are T-cells activated?
T-helper cells are activated through binding APC that has complementary MHC II marker to their TCR and the release of cytokines
Cytotoxic B-cells are activated by the release of cytokines from T-helper cell
How are B-cells activated
B-cell is activated by the T-helper cell’s t-cell receptor binding to the B-cells MHC II marker, releasing cytokines and thus, activating it
what is the primary exposure and what happens upon primary exposure? antibodies?
- response arising from the first encounter of a B or T lymphocyte with a specific antigen
- IgM antibodies are mainly produced
- After initial encounter, b and t cells form memory B and T lymphocytes and there are constantly low levels of antibodies
What is the secondary exposure? what happens in it? antibodies?
response arising from subsequent exposure to same antigen
- Immune response is faster, larger and stronger
- antibodies are produced at a greater rate and cytotoxic t-cells are produced more rapidly
- IgG antibodies are predominant antibodies produced during secondary exposure
