Immunology 6: Elements of the Immune System

Question 1

Basic subunit of Antibodies

Answer 1

2 light chains (220 AA, first 110 different, last 100 common between different light chains)
2 heavy chains (4-5 equal sized domains)

Question 2

Regions of a light chain

Answer 2

first half = variable region/domain

last half = constant region/domain

Question 3

Domains of the heavy chain

Answer 3

1st: highly variable
others: determine class of antibody. Within same class, are identical (constant)

Question 4

__ different constant heavy chain regions

Answer 4

7

-for the classes of IgM, Iga, IgE, IgG1, IgG2, IgG3, IgG4

Question 5

IgE and IgG molecules

Answer 5

1 basic unit

• variable regions of 1 heavy and 1 light chain make 1 antigen binding site
• IgG can activate complement to cause cell lysis

Question 6

IgA

Answer 6

1 or more basic units

• variable within 1 individual and between species
• cannot activate complement to cause cell lysis

Question 7

IgM

Answer 7

5 units

• valency of 10
• most efficient in activating compliment to cause cell lysis

Question 8

All antibody molecules can ___.

Answer 8

Bind to more than 1 molecule of antigen

• most antigens can bind to more than 1 molecule of antigen
• causes lattice formation

Question 9

Lattice formation

Answer 9

• precipitin reaction bc of this
• can see individual molecules of antibodies since much larger than antigen
• antigen ‘joined’ antibody molecules together make triangles & quadrilaterals

Question 10

Number of different kinds of antibodies that can be produces are ____.

Answer 10

Very large

-diverse

Question 11

Diversity in antibody chains reflects ___.

Answer 11

corresponding diversity of genes coding for said chains

Question 12

Clonal Selection Theory basic elements (3)

Answer 12

• Selection
• cells able to respond to antigen are clonal
• Self-nonself discrimination

Question 13

Selection (element of clonal selection theory)

Answer 13

• antigen strongly interacts with specific antibodies (selects them) which results in further production of them
• Selection theory: antigens select good fitting antibodies from vast array that are premade and waiting to be selected

Question 14

Cells that respond to antigen are clonal (element of clonal selection theory)

Answer 14

• individual cells express genes coding for 1 antibody with unique specificity, and bear the corresponding antibody as a receptor
• interaction of antigen with their antibody receptor results in multiplication of cell & its differentiation to produce the antibody
• Clonal Selection theory: antigen can selector precursor cells with correct antibody receptors, cause their division to make clones which will differentiate to make/secrete lots of antibody

Question 15

Set of related cells derived from one parent?

Answer 15

Clones

-parent is precursor cell

Question 16

Each precursor cell only makes ____.

Answer 16

1 antibody

-must be many different precursor cells then

Question 17

Clonal Selection theory accounts for?

Answer 17

Natural time needed for body to respond
-since precursor cells specific for a certain antigen are rare, takes time to multiply and make sufficient antibody producing cells that can make detectable antibody

Question 18

Self-nonself discrimination (element of clonal selection theory)

Answer 18

• form clonal theory, supposed generation of so many precursors with different antibody receptors would inevitably result in some binding self-antigens
• mechanism to prevent this and only allow responses against foreign antigens

Question 19

Evidence for Clonal Selection Theory (1)

Answer 19

-removing cells able to bind to antigen sheep RBC from a spleen abolishes ability for spleen to make antibody to SRBC but can still make other antibodies to other antigens: cells binding to a certain antigen are required to make antibody to only that antigen

Question 20

Evidence for Clonal Selection Theory (2)

Answer 20

-chickens normally make antibodies to turkey RBC’s, but if a developing chicken (egg) is injected with turkey RBC’s it does not produce said antibodies if injected again as a young chick: self-antigens are present early in development and continuously after which distinguishes them from foreign antigens

Question 21

Major Histocompatibility Complex (MHC) molecules

Answer 21

class of molecule that performs central role in recognition of antigens

Question 22

Kinds of MHC molecules

Answer 22

• Class 1: found on surface of all cells of body
• Class 2: found mainly on phagocytic cells
• both classes have shallow groove where peptides ~10 AA in length bind

Question 23

Purpose of MHC class 1 cells

Answer 23

• representation of peptides derived from proteins synthesized in the cell & intracellular proteins
• most of these peptides made early on in development and throughout life and regarded as self (generates no immune response)
• If new viral/mutation peptides made on surface of cell, MHC 1 molecules part of signalling system to identify non-self proteins and inform immune system to attack

Question 24

Purpose of MHC class 2 molecules

Answer 24

-once phaogcytes engulf and degrade antigens, present peptides to groove of class 2 molecules, expresses (on surface of cell) peptides as foreign

Question 25

MHC molecule variation

Answer 25

• occur in mice -> men
• many allelic genes coding for protein chains to make up molecules (grooves all different)
• if grooves of MHC 1 all same, a variant of a virus might not make peptides able to bind to the groove and thus could multiple in that cell, not have the immune system realize its infected and would not attack it. Virus like this could wipe out entire population
• If many different types of MHC 1 grooves, highly unlikely none of the peptides wouldn’t be able to bind to any of the grooves present in population: protects entire population

Question 26

Antigen Specific B and T cells

Answer 26

B cells: precursor cells for antibody production, made in bone marrow
T cells: carries out and regulates immune responses, made in thymus. DO NOT bind antigen itself, bind peptides derived from antigen bound to MHC molecules

Question 27

Lymphoid organs

Answer 27

Adenoids, tonsil, thoracic duct, left subclavian vein, lymph nodes, thymus, spleen, Peyer’s patches, SI and LI, appendix, bone marrow, etc.
-where antigen induces immune responses

Question 28

T cells bearing CD4 antigen bind ___.

Answer 28

Peptides bound to MHC class 2 molecules

Question 29

T cells bearing CD8 antigen bind ___.

Answer 29

Peptides bound to MHC class 1 molecules
-central part of surveillance machinery that recognizes infected cells or those that are malignant