Chapter 9 (Exam 3) Flashcards by Olivia Hofer

Functions of Antibody Response

Neutralization
Opsonization
Complement Fixation

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Signaling in B cells

Clustering of Receptors
B cell coreceptor
Activation of intracellular kinases

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How is signaling generated in B cells?

Crosslinking Igs with repetative epitopes of antigens
Causes clustering and aggregation of Iga and Igb

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B cell signaling is increased with

Coreceptors

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Thymus-Independent (TI) Antigens

Repetitive carbohydrate or protein epitopes at high density on pathogen surface

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TI antigens are able to

Activate B cells without Ag-specific helper T cells
Mostly B-1 cells

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Antibodies most produced by TI activation and why?

IgM
no SHM or isotype switching

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B cells must interact with ____ to survive

Follicular dendritic cells (FDCs)

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Follicular Dendritic Cells (FDCs)

Help create B cell follicles in lymph node

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On dendrites, ____ and ____ hold complement-coated antigens and pathogens.

CR1

CR2

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Immune complexes

held on surface, not degraded

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B cells home to lymph nodes by

CCL21 and CCl19
Drawn to primary follicle by CCL13

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Cognate Interaction
(conjugate pair)

B and T cell specific for different epitopes of same pathogen

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Events required for B cell activation

Surface Ig binding to antigen
T cell help

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What cytokines induces B cell differentiation?

IL-5, IL-6, IL-21 from Tfh cells

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How do B cells become plasma cells?

Conjugate pair moves into medullary cortex
cells divide to form primary focus
B cells secrete IgM

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IL-5, IL-6, IL-21

Induce terminal differentiation

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Primary focus

Produce first Ab

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Secondary focus

Produce many B cells with affinity matured, switched Abs
Germinal Centers

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Germinal Center Reaction

Swollen Glands
B and T cell proliferation in secondary follicle

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Centroblasts

in dark zone
Proliferate
Do not express surface Ig
Cannot interact w FDC
undergo SHM and switching

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Centrocytes

in light zone
no proliferation
express affinity matured, switched Ig

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Centrocytes undergo _____ unless surface Ig binds antigen and ____ is bound by ____ ligand.

Apoptosis

CD40

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When does B cell express Bcl-xL?

B cell induced by FDC to internalize, process, and present Ag to Tfh cell

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Affinity matured centrocytes selected to survive will become

plasma cells long-lived memory cells

Genetic deficiency in CD40 ligand

hyper-IgM syndrome

IgM activates

classical pathway of complement

Functions of circulating IgM, IgG, and IgA

Defend all tissues reached by blood Prevent blood-borne infection

Dimeric IgA

Transported to child trough breast milk Passive transfer of immunity

Lowest levels of IgG

age 3-12 months Most susceptible to infections

IgG is delivered to tissues using

FcRn

poly-Ig

Binds constant domains of dimeric IgA and IgM

Cell types involved in IgE response and what they express

Mast cells, eosinophils, basophils Express FceRI to bind constant region

Antibody Effector Functions

1. Neutralization 2. Activation of Complement 3. Uptake and degradation of pathogens vis Fc 4. Facilitate killing of targets by NK cells 5. IgE response

Neutralizing Abs to prevent VIRUS entry

Bind on surface of cells with influenza hemagglutinin Virus cannot infect

Neutralizing Abs to prevent BACTERIA entry

F protein binds fibronectin Abs prevent attachment to tissues

IgG and IgA Abs neutralize

toxins and venoms

Treatment for venoms

passive immunization of Abs raised in animals

IgM can activate classical complement effectively due to

Pentameric structure 5 binding sites for C1q on IgM

What other isotype can activate classical complement pathway?

IgG

Removal of immune complexes

by erythrocytes

Fc receptors are expressed on

neutrophils, basophils, mast cells, dendritic cells, macrophages, FDC, and NK cells

a single mast cell has bound IgE molecules

specific for many different antigens

cross linking of FceRI

by IgE binding and clustering triggers rapid mast cell granule release

mast cell, basophil and eosinophil granule contents are

inflammatory mediators

what do inflammatory mediators do in an IgE response?

induce contraction of SM cells increase blood vessel permeability attack parasite directly

what are the natural targets of IgE

unicellular protozoa multicellular invertebrates (worms, flukes) ticks mites

ITAMs on g chain

signal to interior

targets of IgE are ________________ than microbial pathogens so _____________________ are needed for removal

much larger different mechanisms

FcgRI signaling

needs to be crosslinked by Ab

Signaling from FcR's bound to Fc regions of Ab's trigger

engulfment which eliminates pathogen and allows for processing and presenting

eosinophils ________________ large parasites coated with IgE

directly attack

in developed countries, the IgE response against _________________ is not frequent, so IgE responses in ________________ is much more common

parasites allergies

ITIM

Suppresses signaling helps control response

if the immune system is unstimulated,

it can respond in unexpected ways

purpose of RhoGAM

inhibits primary immune response to Rh so fetal erythrocytes are not destroyed and babies are healthy

Why have a variety of low-affinity Fc receptors for IgG?

Help control immune responses receptors with ITIM motifs

FcaRI binding to monomeric IgA

medium-affinity

FceRI binding to IgE

very high affinity mast cells, eosinophils, basophils

if a Rh- mother is carrying a second child that is Rh+ and does not take RhoGAM, what happens to the baby?

secondary immune response with high affinity IgG massive destruction of fetal erythrocytes triggered by anti-Rh IgG hemolytic anemia of the newborn

ADCC

Antibody dependent cell-mediated cytotoxicity

if a Rh- mother is carrying her first child that is Rh+ and does not take RhoGAM, what happens to the baby?

low affinity IgG and IgM minor destruction of fetal erythrocytes healthy newborn baby

purpose of the FcgRIIB1 receptor

crosslinks with Ig and sends an inhibitory signal to prevent naive B cell activation

is there a FcgRIIB1 receptor on memory B cells?

no! so they can get activated!

Therapeutic use of ADCC

Rituximab eliminates B cells and tumors by ADCC monoclonal Ab targeting CD40