Humoral Immune Responses Flashcards by Staci Thomas

What is expressed on mature naive B cells?

BCR -- IgM, IgD, Ig-alpha, and Ig-beta 
Co-BCR -- CD19, CD81, and CR2 (CD21) 
MHC Class II
CD40
CD20

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B-2 cells can be divided into two major subsets, which are…

– Follicular B cells (recirculating B cells – majority)

– Marginal B cells (reside in spleen – blood borne polysaccharide Ags)

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B-1 cells are located where?

Mucosa – have limited Ag specificity

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Naive B cells travel to secondary lymphoid tissue. The primary lymphoid follicles are the spleen and lymph nodes. They enter the spleen through the ________ and lymph nodes via the _______.

Blood

Lymphatics

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Activated (presented by DCs) T cells reduce expression of the chemokine receptor ________, which recognizes chemokines produced in T cell zones, and they increase expression of _______, which binds a chemokine produced in B cell follicles.

CCR7

CXCR5

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Activated (antigen-stimulated) B cells decrease expression of _______ and increase expression of _______, exactly the opposite of T cells. As a result, antigen-stimulated T and B cells migrate toward one another and meet at the edges of the lymphoid follicles or in inter-follicular areas.

CXCR5

CCR7

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When a B cell is not activated (no antigen) it uses _______ to migrate to the primary follicle.

CXCR5

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What do B cells use to pass through the secondary lymphoid tissue?

HEV

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Once B cells are in the primary follicle, they receive a signal to survive from ______.

FDCs (follicular DCs)

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Within the primary follicle, there are too many B cells and not enough FDCs to provide survival signals. As B cells exit through the efferent lymphatic vessel, there is competition for the survival signals. What happens to naive B cells within weeks of not receiving survival signal/antigen?

They die

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Antigen binds to membrane bound ______ on naive B cells and activates them.

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Activation of B cells can occur in two ways, which are…

T-dependent

T-independent

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How many signals are required to completely activate a B cell?

2 signals

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In the first signal of BCRs, they must ________ 2 or more BCRs to create a strong signal. The signaling itself occurs through the ______ and ______ cytoplasmic tails that contain ITAMs.

Crosslink
Ig-alpha
Ig-beta

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The intracellular signaling steps in B cell activation are identical to those of T cells except for the Src-family kinase used in the initial signaling step. B cells use _____, while T cells use ______.

Syk

ZAP-70

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Cross-linking of BCR by antigen generates a signal that is necessary but NOT sufficient to activate naive B cells. Ag with bound ______ is recognized by membrane Ig and ______. ______ provides cross-linkage for signaling.

C3d
CR2
CR2

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Signaling occurs through Ig-alpha and Ig-beta, CR2 and ______ cytoplasmic tails (BCR co-receptor complex).

CD19

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If there is no C3d attached, the use of ______ can recognize PAMPs and develop a signal.

TLRs

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After activation by Ag in the follicular area (lymph node), B cells change their chemokine receptor expression and migrate where?

Edge of the follicular zone

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Activated B cells secrete low levels of _______ and increase expression of co-stimulatory molecules and cytokine receptors.

IgM

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What are TI-1 (T-independent) microbial agents often called that can activate B cells in high concentrations?

Mitogen

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The co-stimulatory signals are generated through the interactions of ______:______ and adhesion molecules.

CD40 (B cell)

CD40L (T cell)

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Co-stimulatory signals induce cytokine modulated class switching, induce _______ enzyme, and affinity maturation (somatic hypermutation).

AID (activation-induced deaminase)

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This enzyme is crucial to the diversification of the antibody repertoire via somatic hypermutation, class switching, and gene conversion. It is a cytidine deaminase and initiates these reactions by delaminating cytidine residues in single-stranded DNA in Ig genes.

AID (activation-induced deaminase)

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After receiving T cell help, B cells change their chemokine receptor expression and migrate to the follicular area and establish _______ _______ in the follicles.

Germinal centers

Activated B cells begin cytokine modulated class switching and affinity maturation of receptors. Successful rearrangements are selected/supported by ______ and ______.

Tfh (follicular T helper cells) | FDCs

Cytokines released by Th cells promote two general functions, which are...

-- Induce H chain class switching -- Augment B cell differentiation and proliferation

This is the term for the introduction of point mutations in the switch regions of the variable areas of the Ig genes resulting in expansion of the Ab repertoire to generate high-affinity antigen-specific Abs.

Somatic hypermutation

This key enzyme of somatic hypermutation converts C's to U's, allowing Ape I endonuclease to create DS breaks in the DNA.

AID

Tfh cells express CD4+ and low levels of ______.

CD25

This is essential for germinal center reaction between Tfh and B cell (inducible co-stimulator/homology with B7).

ICOS (Tfh) | ICOS-L (B cell)

What do Tfh secrete that facilitates differentiation of B cells into plasma blasts?

IL-21

What do Tfh secrete for cytokine switching?

IFN-y | IL-4

Selective survival of the B cells producing the (LOWEST/HIGHEST) affinity Abs occurs in the germinal centers.

Highest

FDC and Tfh are interactions with high affinity B cells is necessary for ________.

Survival

These are terminally differentiated effector B cells. They have decreased CD19, CD20, MHC II and increased CD27. They are dependent on soluble Ig.

Plasma cells

What are the effector molecules of humoral immunity?

Abs

This type of B cell responds to T-independent responses (non-protein) Ag in mucosal tissues.

B-1 cells

Marginal zone B cells (_____) in spleen recognize blood-borne polysaccharides.

B-2 cells

This type of B cell survives for long periods to time without additional Ag stimulation.

Memory B cells

Memory B cells express high levels of the anti-apoptotic protein ______, which contributes to their long life span.

Bcl-2

What are the surface markers of memory B cells?

CD27 | CD45R

Antibody feedback is a control mechanism triggered by secreted Ab that blocks further Ab production (negative feedback). The only Ig that does this is...

IgG

Humoral immunity is the principle defense against (EXTRA/INTRA)-cellular pathogens.

Extracellular

The effector functions of Abs are mediated by the _____ region. Different isotypes serve different effector functions. Although the effector functions are mediated through this region, all functions are triggered by the binding of Ag to the ______ region.

Fc | Fab

Isotope switching diversifies functional properties. Fc region contains binding sites for ________ and _______.

Complement FcR (Fc receptors) ***FcR on located on cell that receives antigen bound to Ab, so the Fc portion of Ab binds to the FcR on cell

This complement pathway is the most rapid and efficient. Activated via Abs.

Classical pathway

T/F. Microbes require a specific Ab to stop it from infecting cells.

False. Any class of Ab works, they just have to bind to the Ag. Some Abs will have higher affinity than others to the Ag though.

Fc receptors on immune cell populations promote _________ and deliver signals.

Phagocytosis

Opsonization allows for clearance of immune complexes (IC). _____ on erythrocytes binds circulating immune complexes with attached C3b and C4b and transports the complexes to the liver and spleen. Phagocytes remove IC from erythrocyte surface.

CR1

_____ cells bind to antibody-coated cells by Fc receptors (FcyRIII) and destroy infected cell.

This is a therapeutic use for rapid protection after exposure. Some autoimmune/inflammatory diseases are treated with it by engaging the inhibitory FcR on B cells and possibly DCs and suppress the immune response.

IV Ig

This is the main natural Ab produced by B-1 and marginal zone B cells.

IgM (some IgG)

IgE binds to _____ receptors on mast cells and eosinophils. Ag binding causes degranulation of the cell, and death of the microbe (helminth).

Fce

These Abs provide protection at the most common portals of entrance, especially mucosal areas.

IgA | IgM

During pregnancy, the mother provides a physical barrier for the fetus against microorganisms. The fetus receives _____ from the maternal circulation and also ______ is secreted through breast milk.

IgG | IgA

______ transports IgG from the maternal circulation across the placental barrier as well as the transfer of maternal IgG across the intestine. It is found on the surface of endothelial cells, macrophages, and other cell types.

FcRn

FcRn does not target bound _____ to lysosomes but recycles the cell surface and releases it at neutral pH, returning it to the circulation.

IgG

After birth, the mother is no longer capable of supplying the baby with IgG and the remaining maternally derived IgG is broken down. Eventually, the infant will begin to produce its own Abs. _____ is produced around birth, _____ and _____ lag 6-12 months leaving a vulnerable period when a baby is not immunocompetent.

IgM IgG IgA

This is the term for an antigenic stimulus that elicits specific adaptive immune responses that can be recalled during subsequent infections.

Immunization

A (ACTIVE/PASSIVE) immunization is the introduction of Ab or antiserum into a naive recipient.

Passive

A (ACTIVE/PASSIVE) immunization is the introduction of an antigen that provokes an adaptive immune response.

Active

A ________ is the intentional delivery of an antigenic stimulus.

Vaccine

An immunization (vaccination) mimics a natural infection. A normal immune response is invoked to destroy and clear the components of the vaccine. The primary immune response results in immunological memory referred to as _______.

Priming

Each subsequent immunization results in increased intensity and magnitude of response. _________ is when repetitive challenge with antigen achieves a heightened state of immunity.

Hyper-immunization

What are examples of passive immunizations?

Snake bite anti-venom | Passive transfer of Ig from mother to child

What are examples of active immunization?

Natural exposure to pathogens | Vaccines

Active immunization has delayed immunity but it is more permanent because it produces immunological ________.

Memory

Combined passive-active immunization is designed to give both immediate, transient protection as well as slowly developing durable protection. Examples are...

Tetanus | Rabies

This is a way in which microbes could evade humoral immunity by preventing complement activation and the binding of Abs and phagocytosis.

An outer capsule or coat on the microbe

Humoral Immune Responses Flashcards

(70 cards)