Adaptive Immune System Flashcards
What are the two types of adaptive immunity?
Antibody mediated or cell mediated
Descrive adaptive immunity’s memory
Its a faster, bigger response - especially if the organism is encountered more than once and its specific for a given organism
What is an antigen
an antibody generator
- any molecule that reacts specifically with the Ag or Ab receptor on a lymphocyte
- does not necessarily have to initiate an immune response
What is an immunogen
An antigen that specifically induces and immune response
What do we want to do for an antigen to work as a vaccine?
We want to evoke a high level of immunogenicity
What is an epitope
its an antigenic determinant
- they’re specific regions of the antigen that are specifically recognized by the adaptive immune response
- usually a stretch of 10 or more AA
Descrive antibody mediated (or humoral) immunity
- the antibody is the main immune cell
- neutralizes free-floating particles (bacteria, toxins, viruses)
- in response to extracellular antigens, the B cells are triggered t proliferate and differentiate into plasma cells
- Y shaped proteins are then called antibodies
- some B cells here form memory cells that respond faster when exposed to the same antigen again
Where are antibodies produced
produced by B lymphocytes (B cells) in the bin marrow of humans or the bursa of birds
What are the 2 structures of an antibody?
2 arms (identical) and a stem
Arms: bind to a specific antigen
Stem: tags the antigen for destruction by other immune system components
What are the two types of antibodies?
Light chain and heavy chain
What are IgG antibodies made up of?
- made of 75% of serum immunoglobulins
- has basic monomeric structure
- 4 subclasses based on AA sequence of the C regions of H chains (IgG1-4)
IgG1 is most prevalent
What part of the antibody does the phagocyte recognize?
The heavy chain
What are the functions of IgG antibodies
- opsonization - enhances phagocytosis, acts as a flag for phagocytes with Fab is bound to the antigen and Fc is freely exposed
- neutralizes viruses and toxins
- main Ab in secondary response when body encounters Ag for 2nd time
- crosses the placenta- passive immunity for fetus from the mother
What are the structure of IgM antibodies
monomeric, when attached to the B cell surface as a receptor
- pentameric in serum, 5 monomers held together by a J chain
What are the function of the IgM antibodies?
- the first antibody produces in the primary response
- Ag recepts on B cells
- activates part of innate defences
- agglutinates particles (bacteria)- can do this because of its pentameric form
How do we know based on antibodies whether or not a person has been infected by a pathogen for the 1st time or the 2nd time?
- if only IgM is in the body, we know that the infection in recent
- if we see IgG, we know the infection has been around for a while
(secondary response gives a high concentration of IgG molecules)
What is the structure and function of IgD antibodies
Structure: monomeric form, found in serum and on B cell surface as a receptor
- less than 2% of total serum antibodies are IgD
Function: unknown!
What is the structure of IgA antibodies and where are they found?
- produced by mucous membranes secretions
- low amount of monomeric form in serum- dimeric form found in secretions
What are the functions of IgA antibodies?
- neutralized bacteria and viruses, preventing them form attaching to mucous membranes
- gives passive immunity from breast milk
What is the structure and function of IgE antibodies?
- monomeric form, low levels found in serum
- Ag receptors on mast cells (tissues) and basophils (in blood)
Function: anaphylactic hypersensitivity
How can antibodies protect against viruses?
the virus can bind to a specific receptor in the host cell and cause infection this way - but if the antibody binds to the receptor and blocks the attachment, the virus will be stopped
- antibodies can protect from toxins the same way as well (by binding to a specific receptor)
What do tetanus shots give us?
Tetanus shots give a small amount of clostridium tent toxin - so that id the body becomes infected with this bacteria, the body would be immune to the effects of the toxin but NOT immune to the effects of the bacteria
What kind of immunity does T cells bring and were do they mature?
- bring cell mediated immunity and mature in the thymus
Do T lymphocytes recognize free antigens?
No, they do not. They recognize antigens if they are presented by one of the body’s own cells
(bacterial or virally infected cells, transplant tissues, cancer)
How do T lymphocytes work?
They bind to the complex of MHC molecules and peptides
- T lymphocytes are activated from here
- T lymphocytes help macrophages kill intracellular parasites
- Th1 cells + MHCClass 2 -> Tcell release macrophage activating factors (interferon gamma)
No radicals involved
- T cells are active ONLY against foreign antigens
What are the 2 major functional populations of T cells
- cytotoxic T cells
- helper T cells
Describe cytotoxic T cells
- differentiate into Tc which destroy infected or cancerous cells -CD8
- recognize Ag presented by MHC class 1 molecules
Describe helper T cells
- differentiate into Th which activate B cells and macrophages - CD4
- Th1 activate macrophages
- Th2 activate B cells
- recognize Ag presented by MHC class 2 molecules
What are MHC molecules?
molecules that present foreign molecules to T lymphocytes
Descrive HIV
HIV recognizes CD4 molecules
- host for HIV is helper T cells
- called a syndrome because it doesn’t kill the patient, it only suppresses the immune system which makes the patient more susceptible to infections that can cause them to die
What is the role of T lymphocytes?
- T lymphocytes help macrophages kill parasites
(Th1 cells + Class 2 MHC -> T cells release macrophage activating factors- interferon game) - no radicals!
- T lymphocytes inhibit cellular replication of viruses (viral infected cells express MHC1 - recognized by Tc cells)
How do macrophages get help from T lymphocytes?
T lymphocyte binds to the macrophage and tells the macrophage to kill the pathogen
- IFNgamma by the helper T cell is released, and the macrophage engulfs and kills the pathogen)
How does the body combat large infectious agents?
- by using antibody dependent cellular toxicity
- effector cells can bind through their surface receptors to Ab molecules coating the target cells
- activation of effector cells
- release of material damaging targets (macrophages, eosinophils, NK cells)
What is the lymphoid system designed to do?
- designed to bring B and T cells in contact with Ags that enter the body
- lymphocytes are highly specific, only recognizing 1 or 2 antigens
What do the lymphatic vessels do?
Carry lymph collected from fluid that bathe the body’s tissues
- lymph goes into surrounding tissues and supply them with oxygen and nutrients from blood
- most fluid reenters capillaries and returns to the heart and lungs, but some enters the lymphatic vessels and travels to the lymph nodes where cells and proteins are removed
What are the primary lymphoid organs?
- bone marrow and thymus
- hematopoitic stem cells develop into B and T cells
- both B and T cells originate in bone marrow, but only B cells mature there
- T cells mature in the thymus
What do lymphocytes do in the secondary lymphoid organs?
gather to collect antigens
What are the secondary lymphoid organs?
lymph nodes, spleen, tonsits, adenoids, appendix
Where are lymphoid system organs located?
- lymph nodes capture Ags from lymph
- spleen captures Ags from blood
What is MALT and SALT
MALT: mucosal associated lymphoid tissue
- plays a key role in adaptive IR that prevents microbes from invading mucosal surface
SALT: skin-associated lymphoid tissue
- prevents microbes from invading skin
How do B and T cell receptors differ?
They differ in surface markers - CD molecule (Cluster of differentiation)
What is the B cells receptor?
The surface immunoglobulin
What is the T cell receptor?
TCRs
Describe colonial selection in B lymphocytes
- only B cells that are capable of making correct antibody can bind to the antigen
Describe colonial expansion in B lymphocytes
- cells that bind antigens begin dividing, producing a population of clones
- somatic mutations allow for further selection
- – the reaction between the B cell and an antigen is the signal that allows the B cells to start dividing (have more B cells that recognize the same antigen)
Do B lymphocytes require 2nd opinions in colonial expansion?
Yes! They require an accessory signals from another Th cell before activation can occur
- helps prevent the immune system from mounting the response against “self”
What is a good way of determining an infection in a patient?
can look to see if a patient has a particular antibody for an antigen (whooping cough) -can use this because the production of antibodies will go up with a specific antigen
Are colonial selection and expansion of B and T cells different?
No! Very similar - the only difference between B and T memory cells is their surface antigens
What are the surface antigens on T memory cells
CD45RO
What are the surface antigens on B memory cells
CD25 and surface IgG, IgA, or IgE
How do B memory cells have a greater combining power?
Through mutation and selection
How do T memory cells have a greater combining power?
through increased expression of accessory adhesion molecules
What activates the classical complement pathway?
the binding of the antibody to the antigen
Explain the events in the classical complement pathway in adaptive immunity?
- the antibody binds to the antigen- this activates the C1 protein
- coverts it to C1qrs - splits C2 and C4, forming C4b2a (this is similar to C3bBb in alternative pathway and is also known as a C3 convertase)
- C3 convertase splits C3 into C3b and C3a
- C3b binds to microbe Ab complex and remaining components join in (C5b, C6,7,8,9) to form a MAC attack
How does neutralization occur by antibodies?
Antibodies prevent the virus/ toxin/ bacteria from attaching to the specific receptor on the host cell by either blocking the virus binding, blocking the receptor, or blocking toxins binding - attaches via the Fab region of the antibody
How do antibodies activate phagocytic cells?
the Fab portion of the antibody binds to the microbial antigens on the virus/ bacteria
- the binding of a microbe to a phagocyte by more than one antibody causes cross-linking of the antibody receptors on the phagocyte surface and triggers phagocytosis of the microorganism - becomes engulfed by the extending cytoplasmic projections
What immunity to B cells control? T cells?
B cells -antibody mediated immunity
T cells- cell mediated immunity
What is the T cell receptor (TCR) on the T cell analogous to compared to a B cell?
Comparable to an antibody
A large number of clonally expanded B cells become what?
plasma- dedicated to the synthesis and secretion of antibodies
What is one major difference between T cell and B cell clonal extension and selection?
T cell receptors do not undergo further selection as a result of somatic mutation
What is the overall goal of clonal selection and expansion in BOTH B and T cells?
To provide memory cells
What is the purpose of memory cells?
they are more readily stimulated by an antigen
- they have a greater combining power
(B cells combine through mutation and selection and T cells combine through an increased expression of accessory adhesion molecules)
** memory cells are the basis principle for vaccination
What are the two methods of lymphocyte stimulation?
T independent antigens and T dependent antigens
How do T dependent antigens work?
T lymphocytes can be activated by interdigitating dendritic cells (naive T cells)
- immature IDC’s take up the antigen which is processed and presented on the surface peptide to the MHC 2
- the IDC migrates to the T cell region of the draining lymph node, where it stimulates several T lymphocytes - binds via the TCR
- primed T cells are more readily stimulated bu the
What are the 2 types of T-independent antigens?
- polyclonal activators - stimulate a wide variety of B cells independently of their specific antigen receptors
- repeating determinants - give rise to low-addinity IgM rather than IgG Ab response and do not induce memory response
Most antigens stimulate B cells only if assisted with what? How does this work?
Only assisted helper T -lymphocytes
- antigen binds to Th and presents the antigen on the B cell surface
- this results in cytosine production to activate B cells which undergo clonal expansion
What are cytokines?
- soluble intracellular communication factors - hormones of the immune system
- these are non-antigen specific molecules
- have a diverse activity
- are important to protect against infectious diseases, contribute to the control of infection and contribute to the development of pathology
The production of cytokines helps define T-heler subsets how?
- there are mutual antagonism between two subsets of Th cells
- – IL-4 down regulates Th1 cells
- – IFNgamma suppresses the activity of Th2 lymphocytes
IFNgamma activates what?
activates macrophages
IL-4 and IL-5 activate what?
B cells, mast cells and eosinophils
