Humoral Immune Response Flashcards
List the 5 classes of immunoglobins.
IgM, IgG, IgA, IgE, IgD
What are the properties and functions of IgM?
- pentamer
- **fixes complement
- first Ig made by fetus and B cells
- high avidity, low affinity
- present in colostrum and mother’s milk (but does not cross the placenta)
- may or may not be produced during secondary immune response
What type of receptors on phagocytes binds IgM?
Fc receptors
-activates complement
What are the properties and functions of IgG?
- monomer
- major serum Ig (most abundant isotype in serum)
- major immunoglobulin of secondary immune response
- **is transported across the placenta
- fixes the complement
What is the major immunoglobulin of the secondary immune response?
IgG
List the four sub-classes of IgG and how they are acquired.
Cg1 Cg2 Cg3 Cg4 the differences are different constant regions of the heavy chain
Why does IgG have a longer lasting immune response?
memory
affinity maturation
Which Ig can be transported across the placenta?
IgG
Which Ig’s can fix the complement?
IgM
IgG
Which Ig’s are opsonins?
IgM
IgG
What two forms does IgA exist?
IgA1 - monomeric
IgA2 - dimeric
Where is IgA found?
in serum and body secretions: tears saliva gastric secretions pulmonary secretions
What two Igs are present in colostrum and mother’s milk?
IgA
IgM
What is the purpose of IgE? structure?
- Fc receptor binds to basophils & mast cells causing degranulation
- parasitic infections (Helminths)
structure: monomer
What is an important mediator in the granules?
histamine
What does histamine do?
increases vascular permeability which creates edema, hives
Where is IgD found? structure?
-on membrane of mature B cells (like IgM)
structure - monomer
What type of organisms activate the humoral response?
extracellular organisms
What are the phases of humoral response?
-B cell gets activated by one antigen
- B cell undergoes clonal expansion and differentiation
Two types (plasma & memory B cells)
Which chains on the B cell undergo rearrangement?
heavy chains
Which chain undergoes class switching?
heavy
Which chromosome is the heavy chain found? light chain?
heavy - chromosome 14
Light
- chromosome 2 (kappa)
- chromosome 22 (lamda)
How do we change immunoglobulins?
triggers which cause class switching: changing of the constant regions
Distinguish between primary and secondary antibody responses.
Primary
- 5-10 day lag
- peak response is smaller
- IgM> IgG
- lower affinity
Secondary
- 1-3 day lag
- peak response is larger
- IgG (IgA, IgE if heavy chain isotype switching)
- higher affinity
IgG has a higher (avidity/affinity)?
affinity
IgM has a higher (avidity/affinity)?
avidity
Which segment gets deleted in class switching?
c segments
Which B cells are T-dependent?
follicular B cells
Which B cells are T-independent?
Marginal zone B cells
B1 B cells
Which B cells are able to class switch?
T-dependent follicular b cells
T-independent B cells are mainly what type of Ig?
IgM
short lived
Where will you find the CD5 marker?
B-1 B cell; not specific
T dependent activation is due to a CD40 ligand binding to a B cell’s ___.
CD40
What type of antigen is present when class switching is activated?
protein antigens
What type of antigen is present in T-independent activation?
polysaccharides, nucleic acid, lipids
In what part of the spleen will B cells be?
white pulp
After a splenectomy, an individual will be susceptible to which organism?
Strep pneumo
What is Hyper IgM syndrome?
- can only produce IgM
- results from mutations affecting class switching
What recognition is required between a Tcell and Bcell for class switching?
Cd40L - CD40
CD28/B7 (CD 88)
Th1 releases cytokines IL4 / IL4R —-clonal expansion
IL5 —differentiation
What would you expect if a Tcell did not have CD40 ligand?
- repeated chronic infections
- elevated IgM but no class switching
- no secondary response available
What happens when FasL is activated?
cell undergoes apoptosis
-important if there was a defective FasL (lymphoproliferative syndrome)
What are the three pathways of the complement cascade?
Classical Pathway (antigen antibody complex) MB-Lectin Pathway (lectin binding on pathogen surface, ) Alternative Pathway (polysaccharides found on bacterial cell wall)
How are the complement cascades different?
activation is different
Where are complements produced?
liver; problems with liver can give you complement problems
Which complement protein has 3 subunits?
C1q
C1r
C1s
Describe the process of the classical pathway.
- Once antibody is bound to antigen, a receptor will bind to C1q. Once complex is bound to C1q, it will activate C1r and then C1s.
- Activates C2 and C4. Cleaves subunits C2a, C2b, C4a, C4b
- C4b and C2b will make C3 convertase.
- C3 is cleaved. C3b, C4b, C2b make C5 convertase.
- C5 cleaved and then C6-9 are added to make MAC complex.
Describe the process of the lectin pathway.
- Mannose binding lectin causes C4 and C2 cleavage.
- C4b and C2b will make C3 convertase.
- C3 is cleaved. C3b, C4b and C2b make C5 convertase.
- C5 cleaved and then C6-9 added to make the MAC complex.
Which components of the complement pathways are inflammatory mediators?
C3a
C5a
Describe the process of the alternative pathway.
- Activated by non-protein antigens. in the presence of Factor D, Factor B will be activated
- C3b and Bb will make C3 Convertase
- C3 will be cleaved
- C3b, Bb, and C3b will make C5 convertase
- C5 cleaved and then C6-9 added to make a MAC complex
What is the function of the complement?
- phagocytosis and killing of microbe
- osmotic lysis of microbe
- destruction of microbes by leukocytes
What is the biological function of C2b?
- prokinin
- associate with edema & cough
What is the biological function of C3a?
anaphylotoxin
What is the biological function of C3b or C4b?
opsonin - promotes phagocytosis
Where are CR1 found?
B cells
phagocytes
RBS
follicular dendritic cells
Where are CR2 found?
Bcells
epithelial
Where are CR3 and CR4 found?
phagocytes
How do bacteria evade the humoral immune response?
- form different antigens
- inhibition of complement activation
- resistance to phagocytosis
