Immunology - Exam 1 (Part 3 - B CELL ANTIBODY)

Why do we need the adaptive immune system?

- Microbes constantly mutating so better able to resist our immune defense

- Our immune system must adapt to keep these mutations from taking over, to be swift and specific, and remember what has been encountered

What are B cells? Where are they produced?

White blood cells that make antibodies

-- produced from bone marrow

T/F: There are 100 million kinds of B cells, and each B cell has B cell receptors that give the distinct types of B cells.

TRUE

What is the difference between a B cell receptor (BCR) and an antibody?

BCR are tethered antibodies; antibodies are free floating

What are the Y shaped proteins that attach to antigens that help to identify and destroy non-self?

Antibodies (Immunoglobins)

Which region of the antibody attaches to the antigen? Which region of the antibody determines the class of antibody, in addition to tethering to the B cell if its a BCR?

Fab region

Fc region

How are the two light chains and two heavy chains held together in antibodies (immunoglobins)?

Disulfide bonds

What is any substance that elicits a specific response by B or T lymphocytes, including foreign proteins, polysaccharides, or lipid (B cell) or protein (T cell), and canalso be components of cell wall, capsule, flagella, toxins, pollen, blood cell surface molecules, and egg whites?

Antigen

What is an antigen a given B cell's receptors recognize?

Cognate Antigen

What is the component of antigen that antibodies interact with?

Antigenic determinant (epitope)

What is the part of the antibody that recognizes and attaches to the epitope?

Paratope

Since we need to be able to make billions of B cells each capable of recognizing a unique epitope, which design gives us 10 million and is mix & match of the variable region?

Modular Design

Since we need to be able to make billions of B cells each capable of recognizing a unique epitope, which design gives us 100 million and is cut or paste?

Junctional Diversity

Since we need to be able to make billions of B cells each capable of recognizing a unique epitope, which process is a combination of heavy and light chains?

Combinatorial Process/Diversity

In the Modular Design, what are the gene segments that code for the antibodies heavy chain? Antibodies light chain?

Heavy chain = (V, D, J, C)

Light chain = VJC

NOTE: The C is the constant region always; the others are variable

In Modular Design, how many V options are there? D? J? What is the C region?

V = 40 options

D = 25 options

J = 6 options

How does Modular design work once the B cell matures?

Chooses one kind of gene segment form the four "buffets" for the heavy chain (V, D, J, C)

For example: could pick number 37V, 12D and 3J.. or any other combination!

In antibody diversity, if the antibody is tethered (BCR), what are the only 2 optinos for the C (constant) region?

M or D

(IgM or IgD)

What mutations are utilized during junctional diversity, where additional nucleotide bases are added or removed when building the antibody in addition to the modular design? Why is this important?

Frameshift mutation (changes amino acid code)

-- MORE diversity (100 million different types of antibodies)

T/F: Antibodies are transcribed and translated differently than other proteins since they are made by B cells.

FALSE

- Antibodies transcribed & translated just like any other protein

Antibodies tag foreign cells/molecules for destruction ("kiss of death"). What 5 ways do antibodies accomplish their function?

1) Agglutination -- clumping antigen

2) Opsonization -- enhance phagocytosis

3) Neutralization -- block viruses and toxins

4) Antibody dependent cell mediated cytotoxicity

5) Complement-lysis -- inflammation

There are _____ classes of immunoglobulins (Ig) since they each have unique roles? They are based on the constant region of which chain?

5 classes (GAMED)

-- based on constant region heavy chain (Fc region)

Which immunoglobulin (Ig) is the predominant antibody in serum (blood), longest lived, and can cross blood vessels such as passing from a mothers blood into the fetus via the placenta? How many subclasses are there?

IgG

-- 4 subclasses

What two methods does IgG use to function as an antibody?

1) Activates Complement (fixes complement through classical pathway)

2) Opsonization (tag pathogen for phagocytosis to help eliminate bacteria, viruses, and bacterial toxins)

Which immunoglobulin (Ig) is the main antibody associated with mucous membranes (found in mucus, breast milk, GI secretions, tears, saliva), given to baby and resistant to enzymatic breakdown, and is the MOST abundant antibody? What structure is it expressed as?

IgA

-- Expressed as a dimer

What two methods does IgA use to function as an antibody?

1) Neutralize pathogens (blocking attachment sites)

2) Agglutination (clustering pathogens together)

Which immunoglobulin (Ig) is the first type to appear in response to antigen recognition, doesn't cross vessels very easily, and is the predominant antibody against RBC antigens? What structure is it expressed as?

IgM

-- pentamer (5)

T/F: B cells will only make IgM unless they can switch classes.

TRUE

What 3 methods does IgM use to function as an antibody?

1) Agglutination (clustering pathogens together)

2) Activates complement (classical pathway)

3) Opsonization (tag pathogen for phagocytosis)

Which immunoglobulin (Ig) is made in response to allergen exposure and binds to the surface of mast cells and basophils, attracking phagocytic cells, and is effective against parasytic worms and large pathogens?

IgE

T/F: On the first exposure of an allergen, histamin is dumped by mast cells/basophils.

FALSE

-- 1st exposure to allergen causes antibodies to be made up and bind to mast cells/basophils

-- 2nd exposure causes mast cells/basophils to dump histamine

What is the biases of allergies?

Antibody dependent cell mediated cytotoxicity

What type of WBC hangs out under body surfaces (skin/mucosa) and lives for many years?

Mast cells

What are the 2 functions of Mast cells?

1) Phagocytize & Opsonize bacteria

2) Protect against parasites -- (dump harsh chemistry (histamine) on parasites and cause inadvertent tissue damage as result)

NOTE: not one of the main phagocytic cells, so if asked, its NOT; phagocytosis is not its main function, remember parasite protection!!

What are the small, local impacts with the degranulation of mast cells harsh chemistry (histamine)?

- Increase capillary permeability (fluid escapes form capillaries to tissue)

- Usually local effect (ex: runny nose)

What are the large, systemic impact with too much degranulation of mast cells harsh chemistry (histamine)?

- Massive degranulation thorughout the body, can decrease blood volume drasticall to point of heat attack or shock

- Contraction of smooth muscle of respiratory tract (difficulty breathing -- suffocation --> anaphylaxis)

Which immunoglobulin (Ig) was the last to be discovered, found in the upper respiratory tract to interact with respiratory viruses and bacteria's and binds with mast cells and basophils, causing release of Cytokines (IL-1, IL-4, TNF), B cell survival factors, and chemokines?

IgD

Antibody Class Summary:

IgG

- Can cross placenta (found in BLOOD)

- OK complement fixer

- Good opsonizer

IgA

- Mucosal secretions

- Protects mucosal surfaces

- Secreted in milk

- Dimer

IgM

- First antibody made

- GREAT complement fixer

- Good opsonizer

- Pentamer

IgE

- Causes allergies

- Defends against parasites

- Causes Anaphylactic shock

Antibodies are made up of ____ heavy chains & _____ light chains?

2 & 2

(NOTE: No difference with B cell receptor, same structure)

What antibodies are attached to the surface of B cells, making it a BCR?

IgM an IgD

T/F: All BCRs on a specific B cell can bind to a few different, but structurally similar antigens.

FALSE

-- All BCRs on a specific B cells are for the SAME antigen

The B cells will spend its life looking for its match (cognate antigen). Most B cells never find its specific antigen and are called ________. If a B cell finds its specific antigen, it becomes activated and is called _________.

No antigen = Naive / Virgin

Antigen/Activated = Experienced

What two signals do B cells need to be activated?

1) Clustering of B cell receptors

2) Co-stimulatory signal

-- T cell dependent

-- T cell independent (pattern recognition)

Which signal for B cells to activate is when B cells encounter its cognate antigen, so the BCR (paratope) binds to the epitope (multiple sites or multiple antigens), causing BVR crosslink?

Clustering of B cell receptors

During BCR cluster/crosslink, what two immunoglobulins interact with enzymes inside the cell? When enough of these immunoglobulins brough to the surface, it triggers a chain reaction to signal what when it becomes strong enough?

Ig-alpha & Ig-beta

--> Strong enough, will activate the nucleus

What receptor can bind to complement protein fragments which are bound to the antigen?

B cell complement receptors

T/F: When BCR and complement receptors are brought together on an opsonized antigen, there is an increased in the BCRs needed to cluster to signal the nucleus.

FALSE

-- decreases BCRs needed to signal nucleus

--> complement not required but when there is a bigger easier response

Which signal to activate B cells is stimulated by the antigen and a helper T cell?

T cell dependent co-stimulation

Which signal to activate B cells is related to antigens that have repeating patterns (repeating disaccharides) and will heavily cluster BCRs, where additional receptors bind antigen or complement?

T cell independent co-stimulation

--> Idependent process from using T cells

What are our phagocytic cells? (3)

What are our antigen presenting cells? (3)

Phagocytic Cells

1) Macrophages

2) Neutrophils

3) Dendritic

Antigen Presenting Cells

1) Macrophages

2) Dendritic cells

3) B cells

NOTE: B cell is NOT phagocytic, but does present its antigen by taking a small piece to present

Will B cells use MHC I (surface of most body cells displaying what is going on in cell, scanned by CTL cells which can kill infected cells) or MHC II (surface of APCs displaying proteins of things they ate, displays whats been killed at battle site and informs Th cells)?

MHC II

What is the 4 step process of T cell dependent co-stimulation?

1) B cell encounters cognate antigen

2) SOME of cognate antigen is endocytosed

3) Peptide fragments of the cognate antigen presented on MHC IIs on the surface of B cell

4) Th cell scans & meets its cognate antigen if its a match (MHC II peptide on B cell)

5) CD40L on Th and CD40 on B cells provides co-stimulation to ACTIVATE B cell

What is it called when the B cell meets its cognate antigen (protein) and the Th cell meets its cognate antigen (peptide fragment from B cell's cognate antigen)?

Dual Confirmation

T cell dependent co-stimulation works great if its a protein fragment, but what happens if the foreign pathogen has carbohydrates or lipids as the antigen?

Some antigens have repeating patterns (repeating disaccharides or lipids -- PAMPs) and will heavily cluster BCRs

-- additional receptors bind antigen or complement, causing cell to activate T cell independent co-stimulation (bypass CD40L-CD40 binding)

What type of antigen does not bind to the BCR receptors on B cells, but instead binds to other receptors, causing clustering of those BCRs anyway, activating the B cell, and making antibodies for nothing?

Mitogen

-- some pathogens rely on this to confuse the immune system since its not something the immune system was designed to do!

What 2 things happen when a signal is sufficient to reach the nucleus and activate the B cell?

1) B cell doubles in size & divides

2) 12 hours/growth and division for about 7 days, resulting in a "clone" of about 20,000 identical B cells

After activation and proliferation (clonal expansion), B cells go through what process?

Maturation process

What are the three parts of the maturation process?

1) Somatic hypermutation --> BCR genes undergo mutation and selection, to create a greater affinity of BCR for its cognate antigen

2) Career decision --> Plasma cells (antibody making) & memory cell (last decades)

3) Class switching --> B cells change class of antibody it produces and is T cell dependent

During somatic hypermutation, instead of there being one mutated base pair per 100 million bases per DNA replication cycle, there is one mutated base pair per ________ bases per DNA replication cycle?

1000 bases

-- very restricted to these chromosomes and these receptors & fine tunes antigen specifically of BCR and antibodies

What is an important feature that somatic hypermutation changes?

Changes antigen binding region of the antibody

-- may increase, decrease, or remain unchanged the affinity of antibody for cognate antigen

T/F: Once maturing B cells begin to proliferate, they can continue to self-stimulate.

FALSE

-- if they are going to continue to proliferate, they need an ongoing signal (must be continually re-stimulated)

B cells mutating toward higher affinity BCRs are ______ stimulated and multiply, while B cells mutating toward lower affinity BCRs are ______ stimulated and multiply

Higher affinity = Easily stimulated and multiply

Lower affinity = NOT stimulated and cease to multiply

Which type of cell in the career decision is the antibody factory that usually goes back tot he spleen or bone marrow to produce 2,000 antibodies per second? What is their lifespan?

Plasma cell

-- live for only a few days

Which type of cell in the career decision waiting for the next time, providing a faster secondary response, and requires Th cell help with CD40L/CD40 coupling? What is their lifespan?

Memory Cell

-- LONG lifespan

T/F: Memory cells are not produced when B cells activated without T cell help

TRUE

What happens when the B cells cut and paste different constant regions?

Class switching

(GAMED)

When a naive B cell is first activated, it makes mainly IgM antibodies... why?

It's the first in line for the Fc region

NOTE: to change, cut off IgM constant region DNA and paste on one of the other constant regions

Why is class switching for antibodies important?

The constant region (Fc) that determines how the antibody functions

(although the part of the antibody binding the antigen stays the same)

T/F: All B cell receptors (tethered antibodies) on any given B cells are identical

TRUE

The T cell dependent co-stimulatory signal for B cell activation?

A. TLR/Ag

B. CD40/CD40L

C. Mitogen/Ag

D. CD8/MHC

B. CD40/CD40L

Besides a BCR on a V cell, name another type of receptor that would likely be present?

A. Complement receptor

B. CD40L

C. Fab receptor

D. IgE receptor

A. Complement receptor

B Cell Summary Slide

- B cells lymphocytes w/ diverse and specific receptors (BCRs)

- BCRs bind to antigens (cognate antigen)

- Activation of B cells = Crosslinking of BCRs & Th cells providing CD40L/CD40 coupling (co-stimulation)

- Proliferation of B cells (clonal selection)

- Maturation of B cells = somatic hypermutation (mutation of Fab region to increase affinity for antigen/cognate antigen), Career choice (plasma cells or memory B cells), and Class switching (type of antibody - GAMED)