Lecture 1 - Antibodies

Question 1

What’s the difference between innate immunity and adaptive immunity?

Answer 1

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.

Question 2

What are the four principles of adaptive immunity?

Answer 2

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).

Question 3

Describe the graph of the kinetics of adaptive immune response

Answer 3

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.

Question 4

What is the outcome of adaptive immune responses?

Answer 4

Protection against toxin and disease causing agents (eg. Bacteria, viruses, parasites).

Question 5

What is a vaccine?

Answer 5

Component of pathogen (or closely related) can be used to induce specific immunity by inducing immunological memory.

Question 6

How do the kinetics of innate response differ from adaptive immune response?

Answer 6

Innate response is rapid and short lived

Question 7

How does innate immunity prepare the adaptive system to respond?

Answer 7

Activatation of the immune cells leads to production of molecules that facilitate T and B cell activation.

Question 8

What is the difference between plasma and serum?

Answer 8

Soluble fraction of blood including clotting factors (plasma) and without clotting factors (serum)

Question 9

What are antibodies aka immunoglobins?

Answer 9

Soluble (mainly serum) proteins secreted by cells of the B cell lineage that bind to offeding agents eg. Pathogens or toxins

Question 10

What is an antigen?

Answer 10

A substance that induces a specific immune response (antibody generating)

Question 11

What is an atigenic-determinant aka epitope?

Answer 11

The site(s) on an antigen that are physically bound by antibodies. Most microbes have many such sites.

Question 12

What is a hapten?

Answer 12

A small molecule that can elicit an immune response only when attached to a larger molecule

Question 13

How were the structure and function of antibodies first studied?

Answer 13

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.

Question 14

What makes an antigen immunogenic?

Answer 14

Must be recognized by cells with immune receptors as foreign, must weight at least 5kD, must posesses a certain degree of chemical complexity

Question 15

Why is the size of an antigen important?

Answer 15

B cells are only activated when their antigen-specific receptors are cross linked by more than one identical epitope

Question 16

How have man made haptens helped immunologists elucidate info about antobodies?

Answer 16

Hapten-protein conjugates can be introduced into animal and the hapten-carrier and immune serum can be collected and analyzed

Question 17

To form a precipitate with a multivalent antigen, what must an antibody possess?

Answer 17

At least 2 antigen-binding sites

Question 18

Describe the basic structure of an antibody molecule?

Answer 18

Two identical heavy chains and two identical light chains. Binding site (aka VL-VH pair) forms from pairing of heavy and light chain

Question 19

How do we know antibody antigen interactions are reversible?

Answer 19

Adding excess hapten to a pre-existing Ab-Ag complex causes the precipitate to resolve

Question 20

How does off rate affect effectiveness of an antibody?

Answer 20

Antibodies with slower off rates/higher affinity for their antigenic determinant have slower off rates (lower Kd) and will remain bound to antigens longer

Question 21

How does multivalency affect antibody effectiveness?

Answer 21

Multivalents remain bound to antigens longer than monovalent; even if one arm dissociates the other may still be bound

Question 22

What is avidity?

Answer 22

The sum total of antigen binding at all of the antigen binding sites

Question 23

Describe antibody domains

Answer 23

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

Question 24

What are framework regions?

Answer 24

Regions important for Ig fold structure and less variant in sequence than CDRs

Question 25

What is an Fab and Fc fragments?

Answer 25

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

Question 26

What differs among antibody isotypes?

Answer 26

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.

Question 27

How does antibody structure change during an ongoing immune response?

Answer 27

Ag-induced Ab are larger earlier in the response than later

Question 28

What are the three basic sizes of serum Abs?

Answer 28

One - two heavy and two light chains (IgE, IgG), two - monomer or dimer (IgA), three - pentamer (IgM)

Question 29

What are the kinetics of different serum Ig's and their induction?

Answer 29

IgM always first isotype, IgG and IgH isotypes produced after

Question 30

What are the different functions of each antibody isotype?

Answer 30

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.

Question 31

How do IgA molecules cross epithelial barriers?

Answer 31

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.

Question 32

What are the four chief effector activities of antibodies?

Answer 32

Opsonization, antibody dependent cell mediated cytotoxicity, complement, neutralization

Question 33

What is opsonization?

Answer 33

Ab of certain IgG subclassees binds to microbes, phagocytes recognyze their Fc receptors and their Fc receptor signals activate phagocytosis of the opsonized microbes

Question 34

What is Ab dependent cell mediated cytotoxicity?

Answer 34

Ab of certain IgG subclasses binds to antigen, NK cells recognize their Fc regions, activated to kill the antibody coated cells

Question 35

What is type 1 hypersensitivity?

Answer 35

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)

Question 36

What is complement avtivation?

Answer 36

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)

Question 37

What is a neutralization reaction?

Answer 37

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

Question 38

How would digestion with pepsin vs papain affect IgG ability to form Ab-Ag complexes?

Answer 38

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.