Section 20.4: B & T lymphocytes and antigen-presenting cells are cells of the adaptive immune response

Name three different APCs. Which is most important for T lymphocyte activation?

Dendritic cells, macrophages, and B cells can all act as APCs. Dendritic cells are most important for T cell activation.

What event (or observation) signals that a B or T cell has achieved immunocompetence?

Development of immunocompetence of a B or T cell is signaled by the appearance on its surface of specific and unique receptors for an antigen. In the case of a B cell, this receptor is a membranebound antibody. (In T cells, it is simply called the T cell receptor.)

T cells must

recognize self major histocompatibility proteins (self-MHC)

T cells must not

recognize self-antigens

What is self-tolerance?

Each lymphocyte must be relatively unresponsive to self-antigens so that it does not attack the body's own cells.

Once these receptors appear, the lymphocyte is committed to react to one (and only one) distinct antigenic determinant because all of its antigen receptors are the

same

In clonal selection, "who" does the selecting? What is being selected?

In clonal selection, the antigen does the selecting. What is being selected is a particular clone of B or T cells that has antigen receptors corresponding to that antigen.

What is a clonal selection?

Process during which a B cell or T cell becomes activated by binding with an antigen

As each lymphocyte becomes immunocompetent, these gene segments are shuffled and combined in different ways, a process called

somatic recombination

Cellular immune response Does not secrete antibodies Targets intracellular pathogens (e.g., virus-infected cells) & cancer cells) In addition, helper T cells coordinate both B & T lymphocyte responses Originates in the red bone marrow Maturates in the thymus Effector cells are Cytotoxic T (TC) cells, Helper T (TH) cells, & Regulatory (TReg) cells Has memory cell formation

T lymphocytes

Which of the following T cells would survive education in the thymus? (a) one that recognizes neither MHC nor self-antigen (b) one that recognizes both MHC and selfantigen (c) one that recognizes MHC but not self-antigen (d) one that recognizes self-antigen but not MHC.

The T cell that would survive is (c), one that recognizes MHC but not self-antigen.

What are memory cells?

that are able to respond quickly after any subsequent encounter with the same antigen

What are effector cells?

the cells that actually do the work of fighting infection

What is the negative selection?

the second test, ensures that T cells do not recognize self-antigens displayed on self-MHC

Lymphocyte development, maturation, and activation: Antigen encounter & activation

When a lymphocyte's antigen receptors bind its antigen, that lymphocyte can be activated

Recognizing self-antigen results in

apoptosis

Failure to recognize self-MHC results in

apoptosis (death by cell suicide)

What are activated macrophages?

are true "killers"—insatiable phagocytes that also trigger powerful inflammatory responses and recruit additional defenses

What are primary lymphoid organs?

thymus and red bone marrow

B & T lymphocytes and antigen-presenting cells are

cells of the adaptive immune response

Because the self-reactive lymphocyte and all of its potential progeny are eliminated, this is called

clonal deletion

Army of identical cells, all descended from the same ancestor cell, is called a

clone

The major types of cells acting as APCs are

dendritic cells, macrophages, and B lymphocytes.

Our genes, not antigens we encounter...

determine which specific foreign substances our immune system will be able to recognize and resist

What are secondary lymphoid organs?

lymph nodes, spleen, MALT

APCs present antigens

to the cells that will deal with the antigens

What is immunocompetence?

1. Ability of the body's immune cells to recognize (by binding) specific antigens 2. Reflects the presence of plasma membrane-bound receptors

Lymphocyte development, maturation, and activation: Proliferation & differentiation

1. Activated lymphocytes proliferate (multiply) and then differentiate into effector cells and memory cells 2. Memory cells and effector T cells circulate continuously in the blood & lymph and throughout the secondary lymphoid organs

What are B cells?

1. Also called B lymphocytes 2. Oversee humoral immunity 3. their descendants differentiate into antibody-producing plasma cells

Lymphocyte development, maturation, and activation: Seeding secondary lymphoid organs and circulation

1. Immunocompetent but still naive lymphocytes leave the thymus and bone marrow 2. They "seed" the secondary lymphoid organs and circulate through blood & lymph

Lymphocyte development, maturation, and activation: Maturation

1. Lymphocyte precursors destined to become T cells migrate (in blood) to the thymus andmature there. 2. B cells mature in the bone marrow 3. During maturation lymphocytes develop immunocompetence & self-tolerance

What are T cells?

1. Lymphocytes that mediate cellular immunity 2. Include helper, cytotoxic, regulatory, and memory cells 3. Also called T lymphocytes

What are dendritic cells?

1. Protective cells that engulf antigens, migrate to lymph nodes, and present the antigen to T cells, causing them to activate and mount an immune response 2. In the skin are sometimes called Langerhans cells

What are antigen-presenting cells (APCs)?

1. do not respond to specific antigens as lymphocytes do 2. play essential auxiliary roles

What is positive selection?

1. is the first of two tests a developing T lymphocyte must pass 2. ensures that only T cells with receptors that are able to recognize self-MHC proteins survive

Lymphocytes become immunocompetent before

meeting the antigens they may later attack

Immunocompetent B and T cells that have not yet been exposed to antigen are called

naive

A specialized cell (dendritic cells, marcophage, or B cell) that captures, processes, and presents antigens on its surface to T lymphocytes

Antigen-Presenting Cells (APCs)

Humoral immune response Secretes antibodies Targets extracellular pathogens (e.g., bacteria, fungi, parasites, some virus in extracellular fluid) Originates in the red bone marrow Maturates in the red bone marrow Effector cells are the plasma cells Has memory cell formation

B lymphocytes

Lymphocyte development, maturation, and activation: Origin

Both B & T cells lymphocyte originate in red bone marrow