DBMB 711: Week 2 Adaptive Immune System Lecture

What are the two main characteristics of adaptive immunity?

Specificity (lymphocytes recognize a specific antigen) and Memory (faster, stronger response on second exposure).

What type of molecule are most antigens?

Proteins, though they can also be lipids or carbohydrates.

How does a primary immune response differ from a secondary immune response?

The primary response is the first time the body sees an antigen; the secondary response is much higher, quicker, and the resulting antibodies/cells persist longer.

Why do vaccines work?

They create a primary immune response and generate memory cells, so if you are later exposed to the pathogen, you mount a rapid and robust secondary response.

What are the two main types of lymphocytes in the adaptive immune system?

B cells and T cells.

What is the general function of T cells?

They perform the cellular response and help with the B cell response.

What is the general function of B cells?

They differentiate into plasma cells, which then produce and secrete antibodies.

Why do lymph nodes swell during an infection?

Lymphocytes in the secondary lymphoid tissue recognize a pathogen, become activated, and proliferate (make many copies of themselves), causing the swelling.

What is the role of C-reactive protein (CRP)?

It is an acute phase protein often used as a clinical marker for inflammation.

What are the two main types of T cells?

Cytotoxic T cells and Helper T cells.

How can you differentiate between cytotoxic and helper T cells?

By their surface molecules: Cytotoxic T cells have CD8, and Helper T cells have CD4.

What does it mean for an antigen-presenting cell (APC) to "present" an antigen?

The APC modifies the antigen and displays it on its cell surface using an MHC molecule for a T cell to recognize.

What is the function of the T cell receptor (TCR)?

It recognizes the specific antigen (e.g., a piece of a virus) being presented by another cell.

What is the function of the CD8 molecule on a cytotoxic T cell?

It recognizes and binds to the MHC class I molecule, which helps solidify the interaction between the T cell and the target cell.

What is the function of the CD4 molecule on a helper T cell?

It recognizes and binds to the MHC class II molecule on an antigen-presenting cell.

What is the primary role of regulatory T cells (T-regs)?

" To ensure the immune system does not react against things it shouldn't (i.e., self-antigens)."

What is the purpose of the "second signal" in T cell activation?

" It is a confirmatory signal required for T cell activation, which prevents accidental activation against something that shouldn't be targeted."

What does MHC stand for?

Major Histocompatibility Complex.

What type of cells have MHC class I molecules?

All nucleated cells (i.e., all cells except red blood cells).

What type of cells have MHC class II molecules?

Only professional antigen-presenting cells (APCs).

What kind of antigens are typically presented on MHC class I molecules?

Endogenous antigens, such as viral proteins from an infected cell or tumor antigens.

What kind of antigens are typically presented on MHC class II molecules?

Exogenous antigens that have been phagocytized and processed by an APC.

What is the role of T helper 1 (Th1) cells?

They are primarily involved in cellular immune responses.

What is the role of T helper 2 (Th2) cells?

Their job is to help with antibody responses by activating B cells.

Why are T helper 17 (Th17) cells important in dentistry?

They are found in high concentrations in mucous membranes (like the oral cavity) and are involved in cellular responses related to periodontal disease and inflammation.

How do cytotoxic T cells kill target cells?

" They release perforin, which perforates the target cell's membrane, and granzymes, which enter the cell and break up its DNA, causing it to self-destruct."

How does a B cell receptor (BCR) differ from a T cell receptor (TCR) in its structure?

A B cell receptor has two antigen-binding sites, whereas a T cell receptor has one.

What is a plasma cell?

A differentiated B cell that is specialized to produce and secrete a large volume of antibodies.

What is the relationship between a B cell receptor and the antibody it produces?

The secreted antibody is essentially the B cell receptor without its transmembrane region; it recognizes the exact same antigen.

What is "linked recognition" in B cell activation?

The B cell and the helper T cell that activates it must both recognize the same antigen.

Explain the process of T cell-dependent B cell activation.

A B cell presents an antigen on its MHC class II molecule to a helper T cell that recognizes the same antigen; the T cell then secretes cytokines, activating the B cell to proliferate (clonal expansion) and differentiate into plasma cells and memory cells.

What does the term "clonal expansion" refer to?

An activated lymphocyte making many, many copies of itself.

What is the function of opsonins?

They coat a pathogen to make it more easily recognized and engulfed by phagocytes ("set the table").

Under what circumstances can T cell-independent activation of B cells occur?

When an antigen, typically a polysaccharide with many repeating epitopes (like on a bacterial cell wall), cross-links multiple B cell receptors at once, activating the B cell without T cell help.

What is the first class of antibody always produced in an immune response?

IgM.

What is "class switching" in antibody production?

The process where a B cell, after initial activation, changes from producing IgM to producing another class of antibody, such as IgG.

What is the most abundant antibody class in the blood?

IgG.

Which antibody class is most associated with mucous membranes, saliva, and breast milk?

IgA.

Which antibody class is primarily associated with allergies?

IgE.

How does IgE trigger allergy symptoms?

IgE binds to mast cells. When an allergen cross-links the IgE on the mast cell surface, it causes the mast cell to degranulate, releasing histamine and other inflammatory mediators.

In a secondary immune response, why is the IgG response so much faster and larger?

Memory B cells have already undergone class switching to IgG, so they can immediately begin producing large quantities of IgG antibodies upon re-exposure to the antigen.