B Cells and Antibodies

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Questions and Answers

Which of the following represents the most accurate depiction of B cell localization for antigen sampling?

B cells are uniformly distributed throughout all bodily tissues, engaging in antigen capture and initiating immune responses at the site of infection.
B cells primarily reside in the bone marrow, intercepting antigens that have directly entered the bloodstream during early development.
B cell follicles within lymph nodes and the spleen serve as key sites for initial interactions with antigens derived from infected tissues, while marginal zone B cells in the spleen monitor blood antigens. (correct)
B cells are predominantly found within the thymic medulla, actively surveying self-antigens to prevent autoimmunity.

Considering the signaling requirements for B cell activation, which statement accurately reflects the current understanding of T-independent and T-dependent responses?

Both T-independent and T-dependent responses initiate identically, diverging only in their capacity to induce memory B cell formation, which is exclusively a feature of T-independent activation.
T-independent responses necessitate direct interaction with cognate T cells presenting antigen via MHC-II, ensuring high-affinity antibody production through somatic hypermutation.
T-independent responses rely on repetitive antigen structures or TLR stimulation, leading primarily to unmutated, low-affinity IgM, while T-dependent responses can involve both early and late responses with potential for somatic hypermutation and class-switching. (correct)
T-dependent responses are characterized by early IgM production, lacking somatic hypermutation, and relying exclusively on pathogen-associated molecular patterns (PAMPs) for activation.

Which molecular event is most critical when initiating the intracellular signaling cascade following B cell receptor (BCR) engagement?

Internalization of the BCR-antigen complex into early endosomes followed by immediate degradation to prevent excessive signaling.
Phosphorylation of Igα/Igβ ITAMs by tyrosine kinases such as SYK, enabling recruitment and activation of downstream signaling molecules. (correct)
Immediate translocation of the BCR complex to the nucleus to directly influence gene transcription.
Direct activation of NF-κB through conformational changes in the BCR complex, bypassing proximal kinases.

How do B cells strategically patrol for antigens?

B cells strategically patrol areas draining tissues for antigens, particularly within secondary lymphoid organs. (B) Signup and view all the answers

Regarding the cellular pathways of B cell activation, what outcome is associated with NF-κB activation downstream of antigen-induced signaling, CD40L, and TLR signaling?

Class switching. (A) Signup and view all the answers

Marginal zone B cells and B-1 cells both arise from the same developmental pathway and exhibit identical antigen receptor repertoires, primarily targeting polysaccharide antigens in the bloodstream.

False (B) Signup and view all the answers

The B cell receptor (BCR) functions exclusively as a signaling receptor, initiating intracellular cascades upon antigen binding, but lacks any role in antigen internalization or presentation to T cells.

False (B) Signup and view all the answers

Describe the critical distinction in signaling pathways between tonic BCR signaling and antigen-induced BCR signaling, focusing on the differential activation of downstream transcription factors and their ultimate impact on B cell fate.

Tonic BCR signaling promotes sustained, low-level activation of PI3K and subsequent transcription of survival genes, whereas antigen-induced signaling amplifies these signals and additionally activates NF-κB and MAPK pathways, driving proliferation, differentiation, and antibody production. Signup and view all the answers

Explain how the spatial organization of B cell follicles within secondary lymphoid organs facilitates efficient antigen capture and presentation, detailing the roles of follicular dendritic cells (FDCs) and subcapsular sinus macrophages in this process.

B cell follicles are strategically positioned to intercept incoming antigens, with FDCs acting as antigen reservoirs displaying antigens to B cells and subcapsular sinus macrophages capturing and transferring antigens to the follicles, enhancing antigen presentation efficiency. Signup and view all the answers

Delineate the specific roles of the SYK and PI3K kinases in B cell receptor (BCR) signaling, contrasting their immediate substrates and downstream effects on B cell activation and survival.

SYK phosphorylates ITAMs on Igα/Igβ, initiating downstream signaling cascades including PLCγ activation and calcium mobilization. PI3K, activated downstream of CD19, generates PIP3, recruiting and activating proteins such as Akt, promoting B cell survival and proliferation. Signup and view all the answers

B cell activation necessitates two signals: engagement of the BCR by antigen, and either T cell help via the ___ interaction or signals through _. These signals dictate proliferation, cytokine secretion and differentiation.

CD40-CD40L, TLRs Signup and view all the answers

Upon B cell activation, the cellular pathway involving PI3K is essential for B cell , whereas the combined signaling via NF-kB and MAPK pathways typically drives _ and proliferation.

survival, differentiation Signup and view all the answers

Match the following B cell types with their functions:

Follicular B cells = Participate in T-dependent responses, undergoing somatic hypermutation and affinity maturation in germinal centers Marginal zone B cells = Respond rapidly to blood-borne pathogens with T-independent IgM production. Plasma cells = Secrete large quantities of antibodies. Memory B cells = Provide rapid and enhanced secondary antibody responses upon re-exposure to antigen. Signup and view all the answers

Match the following signaling molecules with their corresponding functions in B cell activation:

SYK = Initiates BCR signaling by phosphorylating ITAMs on Igα/Igβ. PI3K = Promotes B cell survival and proliferation via Akt activation. NF-κB = Regulates expression of genes involved in B cell activation, differentiation, and antibody production. MAPK = Contributes to transcriptional regulation and cellular proliferation downstream of BCR signaling. Signup and view all the answers

How does the B cell receptor (BCR) facilitate antigen presentation?

The BCR endocytoses and processes antigen, presenting it via MHC class II molecules to T helper cells. (C) Signup and view all the answers

What is the predominant isotype produced during T-independent B cell responses?

IgM (B) Signup and view all the answers

Follicular dendritic cells (FDCs) directly stimulate B cells through cognate peptide-MHC interactions, providing a critical signal for B cell activation within germinal centers.

False (B) Signup and view all the answers

Contrast the roles of early and late signaling events following B cell receptor (BCR) ligation in determining B cell fate decisions, focusing on the activation of specific transcription factors and their downstream effects on proliferation, differentiation, and survival.

Early signaling events primarily trigger survival pathways via PI3K/Akt activation, while sustained and amplified signaling leads to activation of NF-κB and MAPK pathways, driving proliferation and differentiation through transcriptional regulation. Signup and view all the answers

The germinal center reaction critically relies on the enzyme ___________, which introduces somatic hypermutations into the immunoglobulin genes, ultimately driving affinity maturation of the B cell response.

activation-induced cytidine deaminase (AID) Signup and view all the answers

Which of the following outcomes is most directly associated with the ability of B cells to present antigen to T helper cells?

Enhanced B cell survival, proliferation, and differentiation into antibody-secreting plasma cells (A) Signup and view all the answers

Flashcards

B cell follicles

Areas in lymph nodes and spleen where B cells interact with antigens.

B cell activation requirements

Requires antigen binding to the BCR and either T cell help OR signals through TLRs.

T-independent responses

Early response antibody, low affinity, and is mostly IgM.

B cell activation summary

B cells patrol draining areas, activation needs two signals, BCR is a receptor, leads to proliferation.