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Immunology Test 1


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Adaptive Immune Response
characterized by the recognition of foreign antigen and including both the humoral and cell-mediated response
Two molecules are involved in the Adaptive Immune Response:
1. immunoglobulins - humoral response

2. TCRs - cell-mediated response
a group of glycoproteins present in the serum and tissue fluids of all mammals.
Some immunoglobulins are carried on the surface of B cells where they act as ____.
An immunoglobulin is considered an antibody when...
it is free in the blood and/or lymph
Five distinct class of immunoglobulins
IgG, IgA, IgM, IgD, IgE
Immunoglobulins are bi-functional molecules. Name the two important areas on an Ig that are important.
1. Fc portion
2. Fab portion
Fc portion of an Ig
binds to receptor on macrophage or to complement porteins; known as effector function - able to effect cells
Fab portion of Ig
antigen binding domain - binds to antigen
Immunoglobulin class and subclass depends on ________.
structure of the heavy chain
The basic structure of all immunoglobulins is a unit consisting of _______ and _______.
- light chain polypeptide chains
- heavy chain polypeptide chains
variable region of immunoglobulin
-top portion of light and heavy chain
-has a lot of variation
-needs to be different in order to recognize thousands of antigens
-accounts for variability
hinge region of immunoglobulin
-allows flexibility, which is necessary in order to extend outward to bind antigen
2 heavy chains are linked by _____ bonds at the _____ region.
disulfide, hinge
The immunoglobulins differ in which chain?
constant heavy chain
Allotypic variation
refers to genetic variation (different alleles at a given locus) between individuals within a species
Idiotypic Variation
variation in the variable domain produces idiotypes. Idiotypes determine the binding specificity of the antigen binding site
Immunoglobulin subclasses
there are subclasses of Ig that have slight differences in their heavy chains. they are named with a greek letter.
IgG subclasses
IgG1, IgG2, IgG3, IgG4 and their heavy chains are called gamma 1, gamma 2, gamma 3, gamma 4
IgA subclasses
IgA1 and IgA2 and their heavy chains are alpha 1 and alpha 2
IgM, IgD, IgE subclasses
there are no subclasses for these immunoglobulins
Function of IgG
-major Ig in normal human serum
-consists of a single four-chain molecule
-the early antibody: 1st Ig class produced in primary response to antigen because it has 10 potential binding sites (for 10 different pathogens)
Function of IgD
-less than 1% of total plasma Ig, but it is present in large quantities on the membrane of many B cells
kappa and lambda
Constant light chains exist in two distinct forms. These are isotypes.
-found in external secretions, such as breast milk, saliva, tears, mucosal surfaces
-has 2 subclasses: IgA1, IgA2
Function of IgE
-scarce in serum, found on surface membrane of basophils and mast cells
-has very short half life until it binds to the Fc receptor on surface of mast cells
-plays role in immunity against parasitic helminths
-associated with allergic diseases such as asthma and hay fever
B cells can have more than one ______ expressed on its surface, both recognize the same antigen, but will only have one ______, ie. are only specific for one antigen.
isotype, idiotype
Isotypic Variation
the genes for isotypic variants are present in all healthy members of a species,gamma1,gamma2,gamma3,mu,alpha1,alpha2,delta,epsilon,kappa,lambda are all present in the human genome and therefore they are isotypes
-isotypic determinants are constant region determinants that distinguis each Ig class & subclass w/in a species
The enzyme ______ cleaves the IgG molecule in the hinge region between Cgamma1 & Cgamma2 to yield 2 identical Fab regions & 1 Fc fragment.
The enzyme _______ generates two major fragments of IgG: the Fab’2, which includes the 2 Fabs + hinge region & the pFc' fragment that corresponds to the Cgamma3 domain
a reason to digest antibodies:
small antibody fragments are used to attach chemicals and target tumor cells (the entire antibody is too large).
Within the variable region of the heavy & light chains are short polypeptide segments that show exceptional variability and are termed _____.
hypervariable regions
Hypervariable regions are located where on the variable regions of the heavy and light chains?
amino acids 30,50,95
Hypervariable regions are referred to as ______, which means _____.
CDRs, which means complementarity determining regions
when amino acids fold, the region at amino acid 30, 50, 95 in both heavy and light chain are the regions that _______________.
the regions that reach out for the antigen.
Framework regions (FRs)
the intervening peptide segments situated between CDRs (hypervariable regions) within the variable regions of heavy and light chains.
In both heavy and light chains, there are ____ CDRs and _____ FRs. (numbers)
-called gamma/delta has a gamma and a delta chain
-present in low amounts (5-10%)
-heterodimeric molecule - made up of two different pp chains
-alpha and beta chain linked by disulfide bond
Both forms of TCR (αβ and γδ) associate with a number of polypeptides which are collectively called _____.
CD3 association with the TCR is necessary for ______.
surface expression of the TCR complex at the cell surface
T/F: CD3 is a part of the TCR receptor
False: CD3 is NOT a part of the TCR receptor but it is necesarry for surface expression of TCR complex.
T/F: CD3 aids in generating diversity associated with TCRs.
False: CD3 has no amino acid variability on different T cells, thus cannot generate diversity.
T/F: CD3 is required for signal transduction
_____ comprises at least 5 invariant polypeptides called γ,δ,ε,ζ,η.
T/F: CD3 is not necessary for T cell activation
False: CD3 is necessary for T cell activation
Important feature of the transmembrane domain:
it contains a negatively charged amino acid rather than being apolar
the cytoplasmic domain of each CD3 contains a sequence motif called _____ that is important for signal transduction.
ITAM (immunoreceptor tyrosine-based activation motif)
What does ITAM do?
interacts with protein tyrosine kinase, which phosphorylates tyrosines on the ITAM sequence and sends signal to the nucleus that tells the promotors of IL-2 and IL-2 receptor genes to start being expressed
What happens in response to IL-2?
-T helper cell proliferation
-B cell proliferation
When is CD3 phosphorylated?
T cell receptor must first bind to peptide and then engage CD3 before phosphorylation of CD3 occurs.
Class ____ MHC is referred to as an open structure because it can bind 13-18 peptides.
Several hundred different allelic variants of Class I and II MHC molecules have been identified. However, one individual only expresses a small number of these molecues. List the number of possibilities for MHC I and MHC II.
MHC I - up to 6
MHC II - up to 12
promiscuous binding
MHC molecules do not exhibit fine specificity of antigen binding of antibodies or TCRs. Instead, a given MHC molecule can bind to numerous peptides and a give peptide can bind to numerous MHC molecules.
Class ____ MHC has a peptide binding cleft that is blocked at both ends. What is the result of this?
-Class I MHC
-as a result, it can bind peptides that contain 8-10 amino acid residues.
Class ____ MHC has a peptide binding cleft that is open at both ends. What is the result of this?
-Class II MHC
-as a result, it can accomodate larger peptides of 13-18 amino acid residues.
Class I MHC molecues bind peptides and present to ______ T cells.
CD8+ T cells
Class II MHC molecules bind peptides and present to ______ T cells.
CD4+ T cells
anchor residues
amino acids found on class I MHC molecules that anchor the peptide into the groove and give the MHC I molecule the ability to bind to a diverse spectrum of peptides.
Locomotion of prokaryotes
1. Flagella
2. Axial filament
Axial filament
-internal flagella
-found in periplasm
-not extending out of cell wall
-move in wiggling motion
-typical of spirochetes
ex. Treponema pallidum
Attachment of Prokaryotes
1. Pili
2. Fimbria
-mutans lacking fimbria
are not pathogenic
-capsule and slime layers
-loose polysaccharide or protein layers surrounding some bacteria
-aid in resistance to phagocytosis
-capsules are tight and slime layers are loose
Peptidoglycan layers
-chains of NAM and NAG
What blocks the cross linkages of the peptidoglycan layer?
Cell wall of Gram + organisms
-stain purple
-very thick peptidoglycan layer
-techoic acids embedded in peptidoglycan
Cell wall of Gram - organisms
-stain pink
-more complex cell wall
-very thin peptidoglycan layer
-outer membrane external to peptidoglycan
-LPS (lipopolysaccharide)
T/F: both Gram + and Gram - cells produce endotoxins
False: Gram - cells produce endotoxins.
Cell wall of Genus Mycobacterium
-stains gram +
-mycolic acids, waxy polysaccharides, embedded within peptidoglycan layer make these organisms more resistant to drying & other environmental factors
Cell wall of genus Mycoplasma
-lack peptidoglycan cell wall all together
Site of aerobic respiration in bacteria
-cytoplasmic membrane
-because bacteria lack mitochondria
Diversity amongst bacterial populations occurs how?
1. Mutations
2. Recombinations
-donor DNA from dead bacterial cell becomes fragmented
-DNA leaves cell when cell dies/bursts
-other cells can pick up free DNA if they are competent
-foreign DNA recombines with host cell DNA
-must occur during active phase of cell growth
ability of cell to pick up foreign DNA
-virus(bacteriophage) carrying viral DNA
-infects cell & causes cell's DNA to fragment
-sometimes the phage capsid assembles w/bacterial DNA instead of phage DNA
-therefore, if phage infects new cell, it does not kill it
-new DNA will find homologous area on bacteria chromosome & crossing over occurs
-replaces segment of bacterial chromosome
-F plasmid (Fertility plasmid) which possesses genes for pilus formation
-pilus is produced & attaches to F- bacterial cell
-through rolling circle replication, a piece of F plasmid & some of bacterial gene is tranferred
-this recombines with second bacterial chromosome
-Hfr(high frequency of recombination) cell
-segments of DNA(aka jumping genes) can move around & are transposable elements
-transposable element is replaced & inserted into plasmid (or vice versa)
-some TE are not replicated but are lost at original location & move around
-believed that Resistance to antibiotics is because of Transposition
-really no way to stop it because it is random
Endospore formation
-helps to surpass adverse conditions
-Genera Bacillus & Clostridium
-in the face of adverse conditions, organisms cease metabolically active state(vegetation) to a dormant state(sporulation)
-endospores are formed
-dehydration w/in spore is believed to be reason that these cells can survive
-increased calcium & dipicolinic(?) acid causes dehydration
-normally boiling cells causes water w/in cell to release steam & cause denaturing
-by removing water, this can't happen
Eukaryotic Structure
-flagella-move in whip-like motion & are made of microtubules
-Cell wall-not all have cell wall
-cell membrane
How do eukaryotic flagella differ from prokaryotic flagella?
-eukaryotic: move in whip-like motion
-prokaryotic: move in 360 degree motion
Eukaryotic Organelles
-nucleus:contains the DNA which is carried on chromosomes
-nucleolus:site of RNA synthesis
-rough ER:site of protein synthesis
-smooth ER: site of protein
-Golgi:protein sorting & glycosylation of protein
Do all eukaryotes have a cell wall?
Not all eukaryotes have a cell wall.
-protozoa lack cell wall
-molds, yeasts, algae have cell wall but it is not made up of peptidoglycan
Types of Eukaryotes
-Fungi: molds & yeasts
-Protista: protozoa, algae, slime molds
-Animalia - microscopic worms (helminths)
-multicellular = one cell/cross wall/another cell
-cross wall = septate
-no cross wall = aseptate
-vegetative hyphae
-reproductive hyphae: spores are formed & used for reproduction
-mycelium = a colony of mold that is visible to the eye
a colony of mold that is visible to the eye
-ovoid structure
-reproduce through budding
-pathogenic upon inhalation
-enter body either directly through skin contact or inhalation
-single celled
-appear like animal cells because lack cell wall
-pathogenic protozoa typically appear in tropical locations
-ingestion in form of cyst
-can be intra or extracellular
actively feeding protozoa
-dormant form of protozoa
-can contaminate water sources
-ingested & switch to actively growing form
-amoebic disentary
-either microscopic or visible to the eye
-enter body either through ingestion (larvae found in meat or pinworm eggs found in soil) or active penetration (muddy water; will break skin and travel up leg) and arthropod bites
-not cells
-particles: phage or viral particles
-can be very small of large
-composed of protein capsid embedded w/nucleic acid either RNA or DNA but not both
-naked or enveloped
__________ are the subunits of a capsid
T/F: A viral capsid is made of both RNA and DNA
False: a viral capsid is made of either RNA or DNA but not both
Types of capsids
1. helical - ex. TMV
2. icosahedral: 20 equilateral triangles forming 12 vertices; most efficient way to hold nucleic acid
3. complex: are neither helical or icosahedral - ex. bacteriophage
viruses that infect bacteria
Virus: naked vs. enveloped
1. naked
-nothing covering capsid
-naked cells survive longer than enveloped
2. enveloped
-virus obtains from host cell a cytoplasmic membrane
-do not lyse host cell but instead exit through a budding process during which they obtain the membrane
Types of Viral Infections
1. Lytic
2. Persistent - always making virus
3. Latent - do not produce viral particles rather latent RNA is present (LAT RNA) and reactivation event causes production of virus
4. Transformation of normal cells into tumor cells
What type of cell are bacteria?
Explain the DNA of bacteria
-have a long ds circular molecule of DNA
-the DNA is tightly coiled in a region called the nucleoid; may also contain extrachromosomal DNA called plasmids
-plasmids may encode toxins and other enzymes that increase the virulence of the
T/F: Bacteria have ribosomes but lack any membrane bound organelles
The NAM and NAG chains of peptidoglycan are connected by what?
LPS layer is composed of a polysaccharide called the ______ and a lipid part called the ______, which has toxic properties, ie. is the endotoxin.
-antigen O
-lipid A
T/F: endospores can stay resistant for years and are able to begin to grow as soon as they are placed
in suitable environmental conditions
Common forms of virus transmission are:
-inhalation of droplets
-in food and water
-direct transfer
-bites of arthropods
Types of Viral Infection
1. Lytic - release of viral particles can destroy the cell- lysis ie. polio or influenza virus
2. Persistant - hepatitis B virus may remain alive and continue to release virus particles at a slow rate
3. Latent - virus remains quiescent and the genetic material of the virus may exist in the host cell cytoplasm ie. herpesviruses or may be incorporated into the genome
4. Transformation of normal cells into tumor cells - by introduction into the host genome of a viral “oncogene” or by viral proteins that induce cells to divide
Innate Defense Mechanisms
1. Inflammatory response
2. Fever
3. NK Cells
4. Phagocytic Cells
5. Soluble Mediators
Inflammatory Respone
-infected/injured cells release chemicals that send an alarm out to the WBC of your body calling them to come to the site of infection
-vasodilation of blood capillaries heading towards infection to aid migration of WBC to site
-capillaries carrying blood away from site are constricted
-incr'd permeability of capillaries allowing phagocytes to reach site of infection, leading to redness, swelling
-blood clots around site prevent microbe byproducts from spreading to other parts forming an abscess
-pus consists of dead inflammatory cells and tissue cells as well as dead and living microorganisms
-optimum growth temp. for most pathogens is 37 degrees
-increase temp to 40 & pathogens cannot grow
How is fever produced?
-macrophages produce & release a small protein called IL-1
-IL-1 sends signal to hypothalamus to raise body temp.
-endotoxins (LPS layer) from Gram negative bacteria are pyrogens which induce fever & shock
NK Cells
-large granular lymphocytes which lack conventional surface markers such as Igs and TCRs
-do not attack invading microbes but body cells that are infected by them
-release perforins that puncture the cell membrane of target cell allowing water to enter causing cell to swell and burst
-lymphocytes (B dddddddddddddddddd& T cells)
Soluble mediators
-Complement proteins that kill microbes
-lymphokines - soluble proteins produced by T cells
ex. IL-2 and Interferon
Complement system
-composed of over 20 proteins
-these proteins circulate in blood in an inactive state
-attach to membrane of encountered bacteria
-proteins form a complex of proteins called the MAC
-insert small holes into membrane of bacteria
membrane attack complex formed by conjugation of 20+ complement proteins
-released by T helper cells
-major player in immune response
-activates B cells to proliferate
-produced by virally infected cells
-released to the surrounding medium
-causes uninfected cell to synthesize a protein which inhibits infection by the virus by degrading its mRNA
Antibodies and TCRs differ in the way they recognize antigen. Explain.
-Antibodies: recognize antigens in solution or on a cell surface and in the proteins native (intact)state
-TCRs: recognize antigen in association with MHC molecules on cell surfaces and the antigen is not in its native state. It is processed or degraded so that it is only a small fragment of original antigen
antigen processing
refers to the degradation of antigen into peptide fragments which become bound to MHC I and II molecules
invariant chain
a polypeptide which associated with (covers)
MHC II molecules in the rough ER in order to prevent the binding of MHC II to intracellular peptides there. These are to be bound by MHC I, which is also in the ER
MHC I and II are synthesized in the ______.
rough ER

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