Humoral Immunity Flashcards by Sophia Skedros

Antibodies are also called

Immunoglobulins

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Function of antibodies

Opsonization pathogen

Neutralized and eliminate pathogen

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Majority of mature B cells reside in

Lymphoid follicles of lymph node and spleen

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B lymphocyte end goal

Antigen recognition and presentation to T cells

Antibody production

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When B and T cells interact with antigen they’re called

Effector cells

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Where are antigens in tissues transported and delivered

Transported to blood

Delivered to follicles via lymphatics and conduits

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____ captures the antigens and takes them to adjacent follicles in the lymph

Macrophages or Dendritic cells

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___ do not need to be processed for B cells to recognize them

antigens

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Where does VDJ recombination happen on immunoglobulin/bcell receptor

Fab

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First heavy chain of B cells

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μ means what immunoglobulin is on the surface of B cells

IgM

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What does the light chain provide

κ και λ

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B cell receptors can bind to _____ types of antigens

T cell receptors mainly binds to _____

All

Peptides

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B cells recognize which antigens the best

Polly: proteins - best
Pockets: polysaccharides
Nose: Nucleic acids
Lips: lipids
Hair: haptens
And Ass: amino acids - worst

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Recognition of antigen by surface BCR triggers _____

INTRACELLULAR signaling pathways
Tyrosine kinase
Protein kinase C
Change in gene transcription

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What is the first signal for B cells

Antigen binding

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What is the purpose of having a second signal for B cell activation

So if B cell does recognize antigen it only gets activated when it needs to not when it binds to any old antigen

Peripheral tolerance

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What has to be activated first before second signal is activated

Innate immune response

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B cells express ___

CD21 aka complement receptor 2 - CR2)

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CD21 recognizes

Complement proteins during complement activation

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CD21 associated with ___ virus

Epstein Barr virus

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What’s another second signal for B cells

PAMPs binding to TLR

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When a B cell is activated what’s next

Clonal selection
a bunch of B cells made that are specific for the pathogen

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Antibody secreting B cell is called a

Plasma cell

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Why are plasma cells bigger than B cells

Because producing tonnnns of antibody’s

Polysaccharide antigens can engage

Multiple receptors on B cell

Early phase involves Ig_ and is T- _____

M Independent

Protein antigens

Need T cell help

IgM is a ___ lived antibody and ___ affinity Ab

Short Low

T cells get ____ from APC

Protein

What does T cell produce during t-dependent B cell activation

Cytokines and CD40 ligand

Activated B cells move towards T cells from a ______

Chemokine gradient

B cells produce _____ during t dependent B cell activation

CD 40

CD40-CD40L interaction stimulates

Antigen specific B cell proliferation and differentiation Heavy chain isotype switching affinity maturation Making memory cells Antibody secretion

T dependent is ideal b/c

Memory, isotype switching etc.

For B and T cells to come together both cells need to be

Activatec

How is B cell activated by T cells

CD40-CD40L interaction

What activates Tcells

B7-CD28 interaction

Who presents B7

Dendritic cells

Who presents CD28

T cells

What does B7-CD28 interaction do

Enhances T cell proliferation and differentiation

Where do B cells start making antibodies with low affinity

Extrafollicular region

Where does a fully developed humoral immune response occur

Germinal center of B cell

Where does all action happen for B cells

Germinal center

Affinity maturation occurs in

Germinal centers of lymphoid follicles

___ is a result of somatic hyper mutation of Ig genes in dividing B cells

Affinity maturation

Low affinity Ab———> high affinity Ab by

Somatic mutations

With _____ a host will produce antibodies of successively greater affinities

Repeated exposures to the same antigen

What drives process of low aff Ab to high aff Ab

Cytokines

What is the OG, initial Ab

IgM

Switching of Ab ___ = isotype switching

HEAVY CHAIN

CD40-CD40L is ____ cell ____

T Dependent

What 4 things does CD40-CD40L do

Isotype switching High aff Ab Memory B cells Long-lived plasma cells

Isotype switching occurs in response to

CD40-CD40L interaction AND Cytokines

Cytokine for IgG

IFNγ

cytokine for IgE

IL-4

Cytokine for IgA

TCF-β

Why are there specific Ab

Because some are more affective against different pathogens

IgG good for

NeoNatal immunity Opsonization + phagocytosis Complement activation

When you think IgG think

Gomp, comp, Nomp Gomp = Opsonization and phagocytosis Comp = complement activation Nomp = neonatal immunity

IgE good for

Against helminths (parasites) Mast cell degranulation

When you see IgE think

Eeeeeeew a worm MAST (de)go Worm = parasite Mast (de)go = mast cell degranualtion

IgA good for

Mucosal immunity

When you see IgA think

AAAAAchoo = Sneezing is from mucosa epithelial

AID

Activation induced cytosine delaminase Enzyme for recombination of class switching

Key points for class swithcing

Recombination involved Through AID enzyme Heavy chain is switched

What kind of cells do not secrete antibodies and are very long lived

Memory cells

Antibody isotype for primary immune response

IgM>IgG

Antibody Isotype for secondary isotype

IgG or IgA or IgE

T independent antigen

Polysaccharides IgM Little affinity maturation Plasma cells are short lived No memory cells

T dependent antigen

Proteins IgG, IgE, IgA There is affinity maturation Long lived plasma cells There are memory cells

Antibodies us Fab for

Binding and blocking harmful effects of microbes/toxins

Antibodies us Fc to

Activate diverse effector mechanisms

What does it mean that a antibody can be flexible

One Ab can bind to two antigens looks like its doing the splits

Affinity vs avidity

Aff = 1 interaction Avidity = sum of interactions Look up pics if need be

What forces does an Ab bind to an antigen

Non covalent reversible ones

What are the 2 subcategories of Antibodies

Direct Ab mediated And Complement mediated

Direct antibody mediated includes

Neutralization of microbes Opsonization and phagocytosis of microbes Antibody-dependent cytotoxicity See pics - humoral immunity - week 8 - slide 50

Complement mediated Ab funcitons

Lysis of microbes Complement activation Inflammation Phagocytosis of microbes opsonized with complement fragments

How does Ab neutralize microbes/toxins

1: binds and blocks from entering epithelial barrier 2: binds and blocks microbe from infecting 3: binds and blocks toxin from binding to cellular receptor

Describe direct Ab mediated opso. And phago.

1. Ab binds by IgG 2. Fc finds to phago cell 3. Fc sends signals to activate phago 4. Phago eats microbe 5. Death to microbe

Describe antibody dependent cellular cytotoxicity (ADCC)

1. Ab bind to microbe on Fab region 2. Those Ab Fc regions are recognized by NK cell 3. The NK cell is activated and now kills See pic - week 8 - humoral - 54

NK 2 receptors are

Activation receptors - antibody coated cells Inhibitory receptors - recognizing MHC I on cells

___ region of the Heavy chain determines Ab

IgM can exist as

Monomer - found on B cell surface as antigen receptor pentamer - usually secreated version

A pentamer of IgM has

5 antibody molecules 10 antigen binding sites per molecule

Which Ab activates complement and through what pathway

IgM Classical

First complement protein to bind to IgM

Pentamer of IgM is good for classical pathway bc

It offers C1 multiple ways to bind

IgG exists as

Monomer

IgG can easily move to tissue bc

Of specialized endothelial receptor

IgG functions

Longest 1/2 life - cuz associated with memory Most abundant in blood Can weakly activate complement classical path Neutralize Opsonization Ab dependent cellular cytotoxicity via NK cells

IgG Fc receptor on phagocyte

FcγR

IgM Fc receptor on phagocyte

FcμR

IgE Fc receptor on phagocyte

FcεR

IgA Fc receptor on phagocyte

FcαR

What Ab can cross placenta

IgG

The long half-life of IgG is bc of its ability to bind to

Neonatal Fc receptor (FcRn)

Which IgG isoforms activate complement system

IgG1 and IgG3 Odd bois

Why does IgM have a low affinity but a high avidity

It naturally has a low aff BUTT combined all those low affinities together with the pentamer structure and it = high avidity

IgA exists as

Monomer or dimer

Monomer IgA function vs dimeric IgA function

M = combine with IgM and IgG to protect all tissues reached by the blood D = protects mucosal surfaces in breast milk

Function of IgE

Clear parasites Involved in allergy and asthma

IgE activates eosinophil which

Helps kill parasites

Where are FcE receptors

Mast cells (CT) Basophils (blood) Eosinophils (mucosa)

What causes sneezing, vomiting, diarrhea

IgE Specifically the cross-linking of receptors leads to release of mediators It acts on smooth muscle to cause “violent” expulsion of pathogen

Binding of ligand to IgD receptor on B cells _____ activation of B cells

Does not lead to

Which Ab activate classical complement

IgM, IgG1 and IgG3