Immunology 6: Elements of the Immune System Flashcards
Basic subunit of Antibodies
2 light chains (220 AA, first 110 different, last 100 common between different light chains)
2 heavy chains (4-5 equal sized domains)
Regions of a light chain
first half = variable region/domain
last half = constant region/domain
Domains of the heavy chain
1st: highly variable
others: determine class of antibody. Within same class, are identical (constant)
__ different constant heavy chain regions
7
-for the classes of IgM, Iga, IgE, IgG1, IgG2, IgG3, IgG4
IgE and IgG molecules
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
IgA
1 or more basic units
- variable within 1 individual and between species
- cannot activate complement to cause cell lysis
IgM
5 units
- valency of 10
- most efficient in activating compliment to cause cell lysis
All antibody molecules can ___.
Bind to more than 1 molecule of antigen
- most antigens can bind to more than 1 molecule of antigen
- causes lattice formation
Lattice formation
- precipitin reaction bc of this
- can see individual molecules of antibodies since much larger than antigen
- antigen ‘joined’ antibody molecules together make triangles & quadrilaterals
Number of different kinds of antibodies that can be produces are ____.
Very large
-diverse
Diversity in antibody chains reflects ___.
corresponding diversity of genes coding for said chains
Clonal Selection Theory basic elements (3)
- Selection
- cells able to respond to antigen are clonal
- Self-nonself discrimination
Selection (element of clonal selection theory)
- 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
Cells that respond to antigen are clonal (element of clonal selection theory)
- 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
Set of related cells derived from one parent?
Clones
-parent is precursor cell
Each precursor cell only makes ____.
1 antibody
-must be many different precursor cells then
Clonal Selection theory accounts for?
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
Self-nonself discrimination (element of clonal selection theory)
- 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
Evidence for Clonal Selection Theory (1)
-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
Evidence for Clonal Selection Theory (2)
-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
Major Histocompatibility Complex (MHC) molecules
class of molecule that performs central role in recognition of antigens
Kinds of MHC molecules
- 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
Purpose of MHC class 1 cells
- 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
Purpose of MHC class 2 molecules
-once phaogcytes engulf and degrade antigens, present peptides to groove of class 2 molecules, expresses (on surface of cell) peptides as foreign
MHC molecule variation
- 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
Antigen Specific B and T cells
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
Lymphoid organs
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
T cells bearing CD4 antigen bind ___.
Peptides bound to MHC class 2 molecules
T cells bearing CD8 antigen bind ___.
Peptides bound to MHC class 1 molecules -central part of surveillance machinery that recognizes infected cells or those that are malignant
