Lecture 1 - Antibodies Flashcards
What’s the difference between innate immunity and adaptive immunity?
Innate is rapid, generally non-specific, usually inflammatory, short term and immediate from start of infection. Adaptive is highly specific, long term tailored. But remember these adaptive systems aren’t isolated from each other and work in tandem or regulate each other.
What are the four principles of adaptive immunity?
Inducible (when antigen is introduced, something changes), specificity (responds only to one antigen), memory (long term protective), non-responsive to self (self-tolerance; doesn’t react/attack to self).
Describe the graph of the kinetics of adaptive immune response
The antigen is produced and there’s a lag phase of several days leading to a primary response. Eventually effector activity starts to decline until when the Ag is introduced again leading to the secondary/memory response which is faster and has a greater amplitude. Vaccination attempts to prime primary/secondary response.
What is the outcome of adaptive immune responses?
Protection against toxin and disease causing agents (eg. Bacteria, viruses, parasites).
What is a vaccine?
Component of pathogen (or closely related) can be used to induce specific immunity by inducing immunological memory.
How do the kinetics of innate response differ from adaptive immune response?
Innate response is rapid and short lived
How does innate immunity prepare the adaptive system to respond?
Activatation of the immune cells leads to production of molecules that facilitate T and B cell activation.
What is the difference between plasma and serum?
Soluble fraction of blood including clotting factors (plasma) and without clotting factors (serum)
What are antibodies aka immunoglobins?
Soluble (mainly serum) proteins secreted by cells of the B cell lineage that bind to offeding agents eg. Pathogens or toxins
What is an antigen?
A substance that induces a specific immune response (antibody generating)
What is an atigenic-determinant aka epitope?
The site(s) on an antigen that are physically bound by antibodies. Most microbes have many such sites.
What is a hapten?
A small molecule that can elicit an immune response only when attached to a larger molecule
How were the structure and function of antibodies first studied?
Protein Ag would be introduced into animal and it’s serum including the antigen and immune serum would be collected. Antigen induced antibodies form precipitate when mixed with immunizing antigen.
What makes an antigen immunogenic?
Must be recognized by cells with immune receptors as foreign, must weight at least 5kD, must posesses a certain degree of chemical complexity
Why is the size of an antigen important?
B cells are only activated when their antigen-specific receptors are cross linked by more than one identical epitope
How have man made haptens helped immunologists elucidate info about antobodies?
Hapten-protein conjugates can be introduced into animal and the hapten-carrier and immune serum can be collected and analyzed
To form a precipitate with a multivalent antigen, what must an antibody possess?
At least 2 antigen-binding sites
Describe the basic structure of an antibody molecule?
Two identical heavy chains and two identical light chains. Binding site (aka VL-VH pair) forms from pairing of heavy and light chain
How do we know antibody antigen interactions are reversible?
Adding excess hapten to a pre-existing Ab-Ag complex causes the precipitate to resolve
How does off rate affect effectiveness of an antibody?
Antibodies with slower off rates/higher affinity for their antigenic determinant have slower off rates (lower Kd) and will remain bound to antigens longer
How does multivalency affect antibody effectiveness?
Multivalents remain bound to antigens longer than monovalent; even if one arm dissociates the other may still be bound
What is avidity?
The sum total of antigen binding at all of the antigen binding sites
Describe antibody domains
N term has hypervariable sequences (aka complimentarity determining regions) important for antigen binding, C term or constant region is important for receptor interactions and effector functions
What are framework regions?
Regions important for Ig fold structure and less variant in sequence than CDRs
What is an Fab and Fc fragments?
Splitting an Ab at the hinge region results in antigen binding portions (Fab) and tail (Fc). Fc can mediate immune effector activities by binding to Fc receptors on different types of cells
What differs among antibody isotypes?
Different heavy chain constant regions which elicit different types of effector activities. 9 exist in humans. Also two different light chain isotypes called kappa and lambda.
How does antibody structure change during an ongoing immune response?
Ag-induced Ab are larger earlier in the response than later
What are the three basic sizes of serum Abs?
One - two heavy and two light chains (IgE, IgG), two - monomer or dimer (IgA), three - pentamer (IgM)
What are the kinetics of different serum Ig’s and their induction?
IgM always first isotype, IgG and IgH isotypes produced after
What are the different functions of each antibody isotype?
IgA mucosal immunity. IgD naïve B cell antigen receptor. IgE defense against helminithicc parasites, immediate hypersensitivity. IgG opsonization, Ab mediated cytotoxicity, neonatal immunity, feedback inhibition of B cells. IgM naïve B cell antigen receptor, complement activation.
How do IgA molecules cross epithelial barriers?
Polymeric IgA binds to receptor on basal surface of cells in gut, airway, secretory glands. Binding induces transcytosis of the polymeric Ig receptor to apical surface. IgA gets cleaved and released by proteases.
What are the four chief effector activities of antibodies?
Opsonization, antibody dependent cell mediated cytotoxicity, complement, neutralization
What is opsonization?
Ab of certain IgG subclassees binds to microbes, phagocytes recognyze their Fc receptors and their Fc receptor signals activate phagocytosis of the opsonized microbes
What is Ab dependent cell mediated cytotoxicity?
Ab of certain IgG subclasses binds to antigen, NK cells recognize their Fc regions, activated to kill the antibody coated cells
What is type 1 hypersensitivity?
Immediate hypersensitivity. IgE binds to mast cells via the Fcepsilon receptor leading to histamine release (causing vascular permeability, vasodilation, bronchial and visceral smooth muscle contraction)
What is complement avtivation?
9 proteins in complement protein (C1-9, 4 comes after 1). C1 binds to the antigen-complexed Ab molecules leading to the production of C3 and C5 convertases which eventually results in cleavage of C5 to begin late steps of complement activation in which a lytic complex (C5-C9) blasts holes into the cell membrane of the cell (can affect neighboring cells and host cells too)
What is a neutralization reaction?
An Ab blocks the binding of a microbe and infection of a cell by preventing the binding of the microbe to the cell, the spreading of microbes from infected cells or blocking the binding of a toxin
How would digestion with pepsin vs papain affect IgG ability to form Ab-Ag complexes?
Pepsin cleaves once giving a bivalent Ag binding unit and Fc fragment, would still function. Paupin cleaves twice giving two monovalent Fab fragments without avidity and Fc fragment, wont work.
