Microbiology: Chapter 15 (Adaptive Immunity)

How many stages of acquired immunity are there?

5 stages

What is the first stage of acquired immunity?

Lymphocytes are produced and differentiate into B cells and T cells

What is the second stage of acquired immunity?

Macrophages detect foreign antigens and present them to lymphocytes

What is the third stage of acquired immunity?

Lymphocytes proliferate and produce clones, including memory cells

What is the fourth stage of acquired immunity?

Activated B cells become plasma cells and produce antibodies

What is the fifth stage of acquired immunity?

Activated T cells differentiate into helper, suppressor, cytotoxic, and delayed hypersensitivity cells

Where do T cells and B cells originate?

Bone marrow

Where do T cells mature?

Thymus

Where do B cells mature?

Bone marrow

What happens during lymphocyte development?

Stem cells produce immature lymphocytes that must undergo developmental changes before they can recognize and respond to antigens.

What happens after B and T cells mature?

They enter circulation and are taken up by lymphoid organs.

What happens during B-cell maturation?

B cells develop specific receptors that allow them to recognize particular antigens.

What happens during T-cell maturation?

T cells develop specific receptors and CD markers under the direction of the thymus.

What are CD receptors?

Surface markers or receptors associated with T cells that help identify their type and function.

Which T cells contain CD4?

Helper T cells

Which T cells contain CD8?

Killer (cytotoxic) T cells.

Which cells contain CD5?

Most mature T cells.

What are the four types of T cells?

• Helper T cells

• Suppressor T cells

• Cytotoxic (killer) T cells

• Delayed hypersensitivity T cells

What is the function of helper T cells?

Stimulate other T cells, B cells, and phagocytes.

What is the function of killer (cytotoxic) T cells?

Directly attack and destroy infected or abnormal cells.

What is the function of delayed hypersensitivity T cells?

Release chemicals that attract and activate other immune cells, contributing to a delayed immune response.

What is the function of suppressor T cells?

Limit the amount of antibodies produced and help regulate the immune response.

What happens when a T cell encounters an antigen?

The antigen binds to the T-cell receptor, sensitizing the cell and leading to its activation and differentiation.

What do activated T cells produce?

Cytokines

What do T cells require before activation?

Antigen recognition along with MHC (self) recognition.

What is an antigen?

A foreign substance that lymphocytes recognize and respond to, triggering an immune response.

What does an antigen need to trigger an immune response?

It must be foreign and contain a specific molecular fragment, called an antigenic determinant, that lymphocytes can recognize.

What is an antigenic determinant?

A specific molecular fragment of an antigen recognized by lymphocytes.

Where do antigens commonly enter the body?

Through the respiratory or gastrointestinal systems, or by penetrating the skin.

Where do intravenously introduced antigens become localized?

In the:

• liver

• Spleen

• Bone marrow

• Kidney

• Lungs

Where do antigens travel when introduced through other routes?

Through lymphatic fluid and into lymph nodes.

What are antigen-presenting cells (APCs)?

Cells that process antigens and display them on their surface bound to MHC receptors so lymphocytes can recognize them.

What is the function of macrophages in acquired immunity?

• Engulf and destroy pathogens through phagocytosis

• Process antigens, and present them to lymphocytes to activate an immune response.

What happens during antigen processing and presentation?

An antigen is processed by an antigen-presenting cell and displayed on its surface bound to an MHC receptor.

What is the first step of B-cell activation?

Clonal selection and antigen binding: a B cell recognizes and binds an antigen through its B-cell receptor or receives the antigen from a macrophage.

What additional cell helps activate most B cells?

A helper T cell.

What happens during the instruction stage of B-cell activation?

The B cell receives developmental signals from macrophages and T cells through chemical mediators.

What happens during B-cell activation?

Signals from membrane receptors are transmitted inside the cell to its nucleus, triggering activation.

What is clonal expansion?

The process in which an activated lymphocyte divides repeatedly to produce a large population of identical daughter cells.

What are the two types of cells produced during B-cell differentiation?

• Plasma cells

• Memory B cells

What is the function of plasma cells?

Produce and secrete antibodies

What is the function of memory B cells?

Remain in the body and help produce a faster response when the same antigen is encountered again.

What happens to plasma cells after antibody production?

They eventually die after producing and secreting antibodies.

What are antibodies?

Proteins produced by plasma cells that recognize and bind to specific antigens.

What is the structure of an antibody?

A Y-shaped molecule made of four polypeptide chains: two identical heavy chains and two identical light chains connected by disulfide bonds.

What is the variable region of an antibody?

The tips of the Y-shaped molecule that contain antigen-binding sites and recognize specific antigens.

What is the constant region of an antibody?

The remaining portion of the antibody whose amino acid composition varies very little among antibodies.

What are the five types of antibodies?

• IgM

• IgD

• IgG

• IgA

• IgE

What is the function of IgM?

It is the first antibody produced during an infection

Where is IgM found?

Found in blood and on B-cell surfaces

What is the function of IgD?

It helps activate B cells

Where is IgD found?

Found on B-cell surfaces

What is the function of IgG?

It provides long-term immunity and crosses the placenta to protect the fetus

Where is IgG found?

Found in blood and tissue fluids

What is the function of IgA?

It protects mucous membranes from pathogens

Where is IgA found and what does it do?

Found in saliva, tears, mucus, and breast milk

What is the function of IgE?

It’s involved in allergic reactions and defense against parasites

Where is IgE found?

Found bound to mast cells and basophils

What is the function of B-cell receptors?

Recognize and bind specific antigens to help activate B cells

What is the structure of a B-cell receptor?

An immunoglobulin molecule consisting of two identical heavy chains and two identical light chains.

What is the function of T-cell receptors?

Recognize specific antigens presented to T cells.

How do T-cell receptors differ from B-cell receptors?

T-cell receptors are much smaller than immunoglobulin B-cell receptors.

What happens to activated T cells after sensitization?

They differentiate into helper, suppressor, cytotoxic, or delayed hypersensitivity cells; some become memory T cells.

What is the function of memory T cells?

Respond to the same antigen during a later encounter.

What is the overall purpose of acquired immunity?

Recognize specific foreign antigens, activate B and T lymphocytes, eliminate threats, and create memory cells for future protection.