B Cell Activation: T-dependent vs. T-independent Antigens

Play an AI-generated podcast conversation about this lesson

Which of the following is a key characteristic that distinguishes TI-2 antigens from TI-1 antigens in B cell activation?

TI-2 antigens are characterized by repetitive carbohydrate or protein epitopes, while TI-1 antigens activate in the absence of T cells. (correct)
TI-2 antigens activate B cells through the innate immunity system, whereas TI-1 antigens activate B cells through T cell help.
TI-2 antigens primarily include lipopolysaccharides (LPS), while TI-1 antigens are mainly cell wall polysaccharides.
TI-2 antigens require direct interaction with T helper cells, while TI-1 antigens do not.

A researcher is studying B cell activation in a mouse model lacking T cells. Which type of antigen would still be capable of activating B cells in this model?

Both TI-1 and TI-2 antigens (correct)
TI-1 antigens only
Thymus-dependent antigens
TI-2 antigens only

What is the first step towards B cell activation involving thymus-dependent antigens?

The B cell presents the antigen to a T helper cell via MHC I.
The antigen directly activates the complement system.
The B cell receptor (BCR) binds to its specific antigen. (correct)
The antigen is phagocytosed by a macrophage.

Which of the following scenarios describes the most likely outcome when a B cell encounters a thymus-dependent antigen?

The B cell internalizes and processes the antigen, presenting it to a T helper cell via MHC II, which then provides the necessary co-stimulatory signals for activation. (B) Signup and view all the answers

Which of the following best describes the role of MHC II protein in B cell activation by thymus-dependent antigens?

MHC II presents the processed antigen fragments to T helper cells, facilitating B cell activation. (B) Signup and view all the answers

A patient is diagnosed with a Streptococcus pneumoniae infection. Which type of antigen is most likely to be involved in the initial B cell response?

A TI-2 antigen with repetitive polysaccharide epitopes. (A) Signup and view all the answers

What is the primary mechanism by which TI-2 antigens activate B cells?

Cross-linking of B cell receptors and co-receptors due to repetitive epitopes. (A) Signup and view all the answers

Lipopolysaccharide (LPS) is a classical example of which type of antigen?

TI-1 antigen (A) Signup and view all the answers

Which region of an antibody molecule is primarily responsible for determining its specificity for a particular antigen?

Hypervariable regions (CDR1-CDR3) (C) Signup and view all the answers

Follicular dendritic cells (FDCs) play a crucial role in B cell activation by:

Binding and preserving intact antigens via complement receptors for presentation to B cells. (B) Signup and view all the answers

The differentiation of B cells into plasma cells or memory cells is primarily influenced by:

The specific cytokines present in the microenvironment. (A) Signup and view all the answers

What is the primary mechanism by which neutralizing antibodies protect against viral infections?

Blocking the virus from entering host cells. (C) Signup and view all the answers

Which of the following mechanisms is NOT a way antibodies contribute to suppressing infections?

Direct killing of infected cells (B) Signup and view all the answers

The transport of IgG antibodies from the bloodstream into the extracellular space is facilitated by:

FcRn receptor (D) Signup and view all the answers

Transcytosis of dimeric IgA antibodies across epithelial cells is mediated by which receptor?

Poly-Ig receptor (C) Signup and view all the answers

Why is the antibody response faster and higher after the second injection of an antigen compared to the first?

Due to the presence of memory B cells generated during the primary response. (D) Signup and view all the answers

What is the primary difference between thymus-dependent and thymus-independent antigens in B cell activation?

Thymus-independent antigens directly activate B cells, while thymus-dependent antigens require T cell assistance. (C) Signup and view all the answers

Which of the following is a characteristic of mature, naive B cells?

They express surface IgM and IgD and are ready to respond to antigen stimulation in secondary lymphoid tissues. (B) Signup and view all the answers

What is the role of Iga and Igb proteins in B cell receptor (BCR) signaling?

They possess ITAMs that interact with intracellular signaling proteins upon BCR stimulation. (D) Signup and view all the answers

How do TI-1 and TI-2 antigens activate B cells differently from antigens that require T cell help?

They activate B cells irrespective of the need for T cell interaction. (B) Signup and view all the answers

Which of the following is NOT a primary function of B cell activation?

Activation of cytotoxic T lymphocytes. (D) Signup and view all the answers

What is the significance of ITAMs (Immunoreceptor Tyrosine-based Activation Motifs) in B cell signaling?

They are phosphorylation sites that initiate intracellular signaling cascades upon antigen binding. (D) Signup and view all the answers

How does the activation of B cells by thymus-independent antigens (TI) differ from activation by thymus-dependent (TD) antigens in terms of antibody isotype switching and affinity maturation?

TI antigens do not induce isotype switching and affinity maturation, while TD antigens do. (B) Signup and view all the answers

A researcher is studying B cell activation and observes that a particular antigen stimulates B cell proliferation and antibody production without T cell involvement. Which type of antigen is most likely responsible for this observation?

A thymus-independent antigen (C) Signup and view all the answers

What is the initial interaction between antigen-stimulated B cells and T helper (TFH) cells characterized by within the lymph node?

Movement to the boundary region, forming a cognate pair. (C) Signup and view all the answers

What key molecular interactions mediate the strong cell-cell adhesion between TFH cells and B cells during their activation process?

TFH's LFA-1 binding to B cell's ICAM along with TFH secretion of CD40 ligand and cytokines. (B) Signup and view all the answers

Following initial activation, where do B-T cognate pairs migrate within the lymph node, and what cellular event is characteristic of each location?

Some move to the medullary cords for proliferation and differentiation into plasma cells, while others move to the primary follicle to form the germinal center. (A) Signup and view all the answers

Within the germinal center, follicular dendritic cells (FDCs) secrete specific cytokines that influence B cell behavior. What is the primary effect of these cytokines (IL-6, IL-15, 8D6, and BAFF) on B cells?

They cause B cells to divide rapidly and become large, metabolically active centroblasts. (B) Signup and view all the answers

Activation-Induced cytidine Deaminase (AID) plays a critical role in the germinal center reaction. What enzymatic activity does AID possess, and what is its direct consequence on B cell DNA?

It removes the amine group from the cytidine base in DNA, initiating somatic hypermutation. (B) Signup and view all the answers

Following somatic hypermutation in the germinal center, what determines whether a centrocyte is 'rescued' from apoptosis?

Having high-affinity B cell receptors (BCRs) for antigen. (C) Signup and view all the answers

How do TFH cells contribute to the function of B cells within the germinal center?

By secretion of cytokines and interacting via their CD40 ligand (CD40L) with the CD40 on B cells, which promotes AID enzyme production. (B) Signup and view all the answers

What is the role of the variable regions of the light and heavy chains in the context of antibody-antigen interactions?

They mediate the recognition of epitope by the antibody through the antigen-binding site. (B) Signup and view all the answers

Naive Mature B Cells

Mature B cells that haven't encountered their antigen.

B Cell Receptor (BCR)

B cell receptors associate with Iga and Igb proteins. These have cytoplasmic tails that contain ITAMS, which interact with intracellular signaling proteins.

Thymus-Independent Antigens

B cells can be activated by thymus-independent (TI) antigens. TI antigens do not need T cells to activate B cells.