Immunology: B-Lymphocytes; Complement; Vaccines

Where do B-Cells originate?

Bone marrow

Describe the lineage of a B-Cell?

HSC, Pro B, Pre B, Immature B, Mature B, Plasma cell or Memory B

What is a HSC marked by?

CD34+

What is a Pro-B cell marked by?

CD38+, CD10+

What is a Pre-B cell marked by?

CD10+, CD19+

What is an immature B cell marked by?

CD19+, CD20+

What is a mature B cell marked by?

CD19+, CD20+

What is a memory B cell marked by?

CD19+, CD27+

What genes are present on the Pro-B cell?

D/J of heavy chain

What genes are present on the Pre-B cell?

V-D/J of heavy chain (constant is mu), and light chains are currently surrogates

What genes are present on the immature B-cell?

Heavy chain complete (VDJ-mu), light chain is now kappa or lambda and the cell is expressing IgM

What cell in B-cell lineage does allelic exclusion take place?

Mature B cell

What cell in B-cell lineage does class switching occur/result in?

Memory B Cell or plasma cell

What cell in B cell lineage expresses a Pre-B cell receptor

Pre B Cell

What cell in B cell lineage expresses IgM

Immature B cell

What cell in b cell lineage expresses IgM and IgD

Mature B cell

After what stage of b cell lineage does the b cell leave the bone marrow and enter the periphery

Leaves after immature B cell (matures in periphery)

During which stage of b cell lineage does self-editing/negative selection occur?

Immature B cell

Which chains can undergo self editing of the b cell

light chains of immature b cell

What are the components of the b cell receptor and their functions?

Membrane bound IG (binds to Ag), and CD79 alpha and beta (transmit activation signals to nucleus)

What are the components of the B Cell Coreceptor and it's function?

CD21, CD225, CD19, CD81 (Enhances signals so less antigen is needed)

What is required for T-Cell independent B-cell activation?

Antigen bound to multiple BCRs on the B-cell

In the case of T-cell independent activation of a b-cell, what will the b-cell produce

A short lived plasma cell that secretes IgM (rapid response)

What is more common: t-cell independent or t-cell dependent activation of a b-cell?

T cell dependent

What is required of t-cell dependent activation of a b-cell?

1. Antigen/Antibody complex

2. Costimulation signal of CD40 and CD40Ligand

What is the region formed in t-cell dependent activation

germinal center

Describe t-cell dependent activation of a b-cell

1. In the follicle, a B-cell captures an antigen and internalizes (B-cell activates). B-cell will present antigen on MHC class 2, where it cognates with activated T-Cell.

2. Activated T-cells arise in the T-cell region, where dendritic cells present a peptide that activates the T-cell's CD4+. This is what cognates with the B-cell in step 1.

3. In the germinal center, the b-cell undergoes two options: Class switching (rearrangement of Fc region of BCR) or Affinity Maturation (killing off low affinity b-cells and replicating B-cell clones with highest affinity for antigen). B cells can differentiate into plasma cells or memory b cells here.

Where do memory b cells develop (and what activates this pathway)?

germinal centers of secondary lymphoid organs, t-cell dependent antigen activation

What receptors can a memory b-cell express

IgG, IgA, IgE

If a memory b cell is activated, what does it do?

Differentiate into plasma cell that secretes necessary antibodies

Where is complement produced?

Liver

What is the general role of complement proteins?

Amplify immune response

What are the three pathways of complement activation (and order of activation?)

Alternative (1), Lectin (2), Classical (3)

What activates the complement - alternative pathway? (and activation unit)

Spontaneous, almost any foreign substance, C3B on cell surface

What is the unique C3 convertase of the alternative pathway?

C3bBb

What are unique proteins of the alternative pathway in addition to C3b and C3bBb?

Factor B, Factor D, and Properdin

What complement pathway is important for infancy when maternal antibodies are lost?

Lectin

What is the lectin pathway activated by?

Mannose-binding Lectin binding to pathogen surface (MBL binds to PAMP)

What are the three recognition proteins of lectin pathway?

MBL, MASP1, MASP2

What is the activation unit of the Lectin Pathway?

C4 and C2 (cleaved by C1s to form C3 convertase)

What is the main-antibody directed mechanism for triggering complement cascade?

Classical pathway

Without antibody, you cannot have this complement pathway?

Classical pathway

What Antibody is most efficient for complement activation (and the other antibody capable of it)

IgM (IgG)

What is the classical complement pathway activated by?

Antigen, Antibody complexes (or c-reactive protein)

What are the recognition proteins of the classical pathway?

C1q, C1r, C1s

What is the activation unit of the classical pathway?

C1 s cleaves C2 and C4 to form C3 convertase

What are the components of C3 Convertase

C2a and C4b

Where do all three complement pathways converge?

C3

After the convergence of C3, what is the next step to occur?

C3 convertase (or C3bBb) cleaves C3 into C3a and C3b. C3a will go off into the fluid to attract phagocytes and release histamine from mast cells (inflammatory response), where C3b will coat the pathogen (opsonize) and interact with C3 Convertase to form C5 convertase.

After the formation of C5 convertase, what is the next step to occur?

C5 convertase (C2a, C4b, C3b) cleaves C5 into C5 a (into the fluid to attract phagocytes and release histamine from mast cells -inflammatory response ), and C5b (begins the mac complex)

What is the mac complex composed of?

C5b, C6, C7, C8, and C9

What does the MAC complex do to a pathogenic cell?

Attaches, punches a hole, allows salts and water into the cell until it bursts (cell death)

What are the recruiting complements (phagocytic cells and inflammatory cells)

C3a, c4a, and c5a

What are the opsonization complements (which is the most important)

C3B(*), C4B

What are the killing complements?

MAC complex (C5B, C6, C7, C8, C9)

What is the role of C1-INH (and pathways affected)

dissociates C1S (cannot make c3 convertase), Lectin and Classical

What is the role of Factor I/H (and pathways affected)

Degrades c3b and c4b (cannot make c5 convertase or c3 convertase) (all pathways)

What is the role of CD59 (and pathways affected)

Prevents C9 insertion (no cell death), all pathways affected

What is the role of S protein (aka Vitronectin) (and pathways affected)

Prevents C5b-C7 attachment to cell (no cell death), all pathways

What is the role of DAF (aka CD55)

Dissociates C2b or Bb from cell membrane (cannot make C3 convertase) (all pathways affected)

What is the most common complement deficiency?

C2

What is the most sever complement deficiency?

C3

What is Paroxymal Nocturnal Hemoglobinuria characterized by?

DAF deficiency, RBC lysing and chronic hemloytic anemia (C3b accumulates on RBCs and no DAF to turn it off)

What is Hereditary Angiodema characterized by?

C1-INH deficiency (allows large immune complexes to initiate complement cascade when they shouldn't, swelling of GI tract, skin, and mucosal membranes)

What are the two routes of complement detection in lab

Measurement of complement as antigen in serum or measurement of compliment function

What are the two tests used for measuring complement as antigen in serum

Radio Immuno-Diffusion

ELISA

What is the test used to measure complement function?

Hemolytic Titration Assay

When using an ELISA to detect complement components in the classical pathway, what do you coat the well with?

IGM

What does Hemolytic Titration rely on?

All components of complement cascade to be present

What is used in Hemolytic Titration Assays for functional capacity of the Alternative Pathway and Classical Pathway, respectively?

AH50 and CH50