L11 Antigens And Antibodies Flashcards
What are antigens
Immunogens that react with specific receptors on b cells or t cells and stimulates a specific immune response
What must the substance be in order to be classified as immunogenic
Foreign to body
What are the most potent immunogens
Proteins with high molecular weight
What are some examples of antigens
Polysaccharides,lipopolysaccharide, lipoproteins and nucleoproteins
What are haptens
Molecule that is not immunogenic by itself
They can be small molecules, nucleic acids lipids or drugs ex penicillin
Cannot stimulate a primary adaptive response except when bound to a carrier protein
How is the hapten strategy used
In conjugate vaccines
Weak immunogen is conjugated to a small strong peptide antigen
What are super antigens
Viral and bacterial proteins that cross link the variable b domain of a t cell receptor to the (MHC) class 2 of antigen presenting cells outside normal peptide binding groove
What does the cross linkage of MHC with variable b domain of t cell do
Activation of signal that induces t cell activation and proliferation in absence of antigen specific recognition of peptides
What is the consequence of super antigens binding to outside of antigen binding cleft
Activate any clones of t cells expressing a particular variable b sequence and thus cause polyclonal activation of t cells resulting in over production of pro inflammatory cytokines which can lead to systemic toxicity
What are the molecules produced during infectious process that act as super antigens
Staphylococcal enterotoxins
Toxic shock syndrome toxin
Exfoliative dermatitis toxin
Streptococcal pyrogenic exotoxins
How are antibodies expressed
Soluble molecules present in serum and tissue fluids and function to protect against microbes extracellular pathogens in blood mucosal surfaces and tissues
Membrane bound antibodies on the surface of b cells function as antigen receptor
What is the major immunoglobulin present in serum
igG
Representing appox 75% of serum antibodies in humans
What does IgG consist of
Two L chains and two H chains held by disulphide bridges
Divided in to variable and constant regions
How many variable and constant domains does L chain and H chain have
L chain: one and one
H chain: one variable and three or more constant
What is the function of variable and constant domain in igG
Variable: involved in antigen binding
Constant: responsible for biologic functions
How many subclasses are there for igG
4
What are protective functions of IgG
Activates complement leading to cell lysis
Acts as an opsonin enchancing phagocytosis
Neutralizes pathogens and toxins
Mediates antibody dependent cell mediated cytotoxicity:lytic destruction of tumor or infected cells mediated by killer cell and binds to Fc portion of bound antibody
Only antibody that crosses placenta
IgG
% of igM in serum and how many units does it consist of and how are they joined together
7%
5 units by j chain
Highest mol weight of Ig
IgM
Formed of 10 L and 10 H
Ig that appears early during specific immune response
IgM
Most effective at activating complement
Major immunoglobulin responsible for mucosal immunity
IgA
Level of igA in serum
10-15%
Predominant class of ig found in extravascular secretions such as milk saliva and tears, respiratory intestinal and genital tracts?
IgA
When is igA a monomer and when is it a dimer
Monomer in serum
Dimer when secreted (2 monomers that contain additional polypeptides)
What stabilizes secretory igA
J chain and a secretory component that is incorporated in to igA when its being transported through an epithelial cell
How many subclasses of igA are there
2
Ig mainly on surface of b lymphocytes
IgD
Ratio of igD and igM in b cells
3 to 1
Also called cytotropic Ab
IgE
What does igE do
Binds directly to Fc receptors present on mast cells,eosinophils and basophils
Involved in elicitation of protective immune responses against parasites and allergens
How does ig class switching occur
Initially all b cells bound to an antigen carry igM specific antigen and produce igM in response to this antigen.
Later,gene rearrangements generate antibodies of same antigen specificity but of diff ig classes so that the ig produced later has the same specificity as original igM but with diff biologic characteristics
Dependent on cytokines released from T cells
What are MABS
Highly specific antibodies produced against a single epitope
How are mabs obtained
By fusion of a myeloma cell with a b cell producing antibodies against a single epitope(derived from spleen of mice)
Hybridoma cell is result
What is the ability of a hybridoma cell
Has ability to produce unlimited quantities of a highly specific monoclonal antibody (murine type)
Humanized one produced by genetic eng
Diagnostic uses of MABS?
As in lymphocyte subsets determination
HLA typing and serological tests as ELISA,chemiluminescence and immunofluorescence
Therapeutic uses of MABS?
Anti tumor therapy,antiallergic, and immunosuppressive therapy to prevent graft rejection
Monomers
Dimers
Pentamer
In igs
Monomers IgD,igE,igG Dimer igA Pentamer IgM
