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Questions and Answers

What are the primary functions of the immune system?

Filtering, storing, and recycling.

Transporting, secreting, and phagocytizing.

Identifying, destroying, and absorbing.

Protecting, differentiating, and remembering. (correct)

What is the function of lymphatic vessels?

Absorb fats and return them to the venous system. (correct)

Transport red blood cells.

Produce digestive enzymes.

Store excess interstitial fluid only.

Where does leukopoiesis first occur?

Thymus.

Bloodstream.

Bone marrow. (correct)

Spleen.

What is true about the thymus gland?

It enlarges during childhood and then starts to atrophy. Signup and view all the answers

Which cells are primarily found in the outermost cortex of lymph nodes?

B-lymphocytes. Signup and view all the answers

What does the spleen NOT do?

Produces red blood cells. Signup and view all the answers

How do T lymphocytes develop?

They mature fully in the thymus after beginning in the bone marrow. Signup and view all the answers

What is one of the components of the lymphatic system?

Lymph nodes. Signup and view all the answers

What feature assists larger lymphatic vessels in transporting lymph?

One-way valves. Signup and view all the answers

What type of fluid circulates through the lymphatic vessels?

Lymph. Signup and view all the answers

What is the primary function of macrophages during phagocytosis?

To recognize and engulf foreign threats Signup and view all the answers

Which statement about complement proteins is true?

Most complement components are made in the liver as inactive proteins Signup and view all the answers

What structure forms when a macrophage engulfs a foreign threat?

Phagosome Signup and view all the answers

Which types of immunity does the adaptive immune response comprise?

Humoral immunity and Cell-mediated immunity Signup and view all the answers

What distinguishes the proteins recognized by the immune system as antigens?

Epitopes, which are specific sites on macromolecules Signup and view all the answers

What initiates the destructive process within a phagosome?

The fusion of the phagosome with a lysosome Signup and view all the answers

Which type of antibody is typically found in higher quantities in mucosal areas?

IgA Signup and view all the answers

What is the primary role of the Membrane Attack Complex in immune defense?

To open pores on target cells Signup and view all the answers

Which is a feature of effective antigens?

They typically have high molecular weight and complexity Signup and view all the answers

How do macrophages identify the location of foreign threats?

Through pattern recognition receptors Signup and view all the answers

What is the primary function of cytotoxic T cells?

Destroy virus-infected and tumor cells Signup and view all the answers

What occurs during negative selection of lymphocytes?

Lymphocytes that bind strongly to self antigens are eliminated Signup and view all the answers

Which type of cell is primarily responsible for maintaining immunological tolerance?

Regulatory T cells Signup and view all the answers

How do memory B cells differ from plasma B cells?

Plasma B cells are long-lived antibody-secreting cells, while memory B cells carry antigen memory. Signup and view all the answers

What is a common outcome of receptor editing in lymphocytes?

The lymphocyte no longer recognizes self antigens Signup and view all the answers

What role do cytokines play in the immune system?

They can act in an autocrine, paracrine, and endocrine manner. Signup and view all the answers

What is the first line of defense against foreign threats?

Skin Signup and view all the answers

Which cells are primarily involved in allergic responses?

Basophils Signup and view all the answers

What unique feature do natural killer (NK) cells possess?

They can induce apoptosis in virus-infected and cancer cells. Signup and view all the answers

What process is primarily associated with macrophages in the immune system?

Phagocytosis Signup and view all the answers

What can result from an overproduction of cytokines?

Sickness and death Signup and view all the answers

Which of the following is NOT a characteristic of the epidermis?

Contains deep blood vessels Signup and view all the answers

What describes the function of memory T cells?

They carry the memory of antigen exposure after the infection has cleared. Signup and view all the answers

What is a function of mucosal membranes in the immune system?

They contain anti-pathogenic substances. Signup and view all the answers

Which immune cells respond first to a site of infection?

Neutrophils Signup and view all the answers

What is the primary function of IgM when secreted on the surface of B cells?

To block antigens Signup and view all the answers

Which mechanism involves the clumping of antigens to enhance recognition by macrophages?

Agglutination Signup and view all the answers

How does VDJ recombination generate variability in antibodies?

By combining gene segments randomly Signup and view all the answers

What differentiates MHC I from MHC II in terms of peptide presentation?

MHC I presents peptides from endocytotic vesicles, MHC II from cytosol Signup and view all the answers

Which antibody is primarily produced during the primary immune response?

IgM Signup and view all the answers

What can contribute to autoimmune diseases according to potential causes?

Triggering an immune response bypassing TH cell involvement Signup and view all the answers

How does aging affect the immune system?

Decreased size and responsiveness of immune tissues Signup and view all the answers

What is the role of the Fc region in antibody function?

Activating complement and recruiting leukocytes Signup and view all the answers

What is a key difference between primary and secondary antibody responses?

Presence of memory B cells in secondary response Signup and view all the answers

In what form does IgM exist on the surface of B cells?

Monomer Signup and view all the answers

What occurs to the thymus tissue with aging?

It is replaced with adipose tissue Signup and view all the answers

What happens during the process of antigen presentation on APCs?

Foreign proteins are internalized and processed Signup and view all the answers

What is a potential consequence of an aging immune system?

Decreased response to new infections Signup and view all the answers

Study Notes

General Function of the Immune System

The immune system protects against foreign threats by recognizing them, responding to them, and remembering them for future, more effective responses.

Lymphatic System

The lymphatic system returns excess interstitial fluid to the venous system.
It absorbs fats from the digestive tract and returns them to the venous system for processing by the liver.
It produces and matures many immune cells.

Lymphatic Vessels

Lymphatic vessels begin as fenestrated capillaries, composed of a single layer of endothelium attached to a basement membrane.
Lymph is transported through progressively bigger vessels, through lymph nodes, until it reaches the vena cava.
Larger lymphatic vessels contain one-way valves and smooth muscle.

The Thymus

The thymus is a flat, bi-lobed organ located in the superior mediastinum above the heart.
It enlarges during childhood and starts to atrophy in the 20s.
Each lobe is comprised of lobules held together by areolar connective tissue.

Bone Marrow

Leukopoiesis begins in the bone marrow.
Maturation of leukocytes occurs in the bone marrow or in other organs depending on the cell type.

Lymph Nodes

Lymph nodes are follicles of lymphatic and non-lymphatic cells surrounded by lymphatic capillaries.
They are supplied by afferent lymphatic vessels and drained by efferent lymphatic vessels.
The outermost cortex contains B-lymphocytes, macrophages, and dendritic cells.
The paracortex contains T-lymphocytes and dendritic cells.

The Spleen

The spleen filters blood, stores erythrocytes, removes defective erythrocytes and platelets, and recycles iron.
It lies between the 9th and 11th rib on the left side of the body.
It contains red pulp and white pulp.
The red pulp contains macrophages, erythrocytes, and platelets.
The white pulp is composed of lymphocytes and macrophages.

Lymphocytes

Lymphocytes contain a single, large nucleus, a small amount of cytoplasm, and a wide range of proteins expressed on their surface.
B lymphocytes develop in the bone marrow.
T lymphocytes begin their development in the bone marrow and complete it in the thymus.
Lymphocytes are classified by surface proteins referred to as Cluster of Differentiation (CD) markers.

T Cells and the T Cell Receptor

Cytotoxic T cells (TC) are designed to destroy virus-infected and tumor cells.
TC cells release perforin, granzymes, and granulysin.
They express CD8 on their surface.
Memory T cells (TM) carry the memory of antigen exposure after the antigen has left the body.
They express CD8 on their surface.
Regulatory T cells (TR) maintain immunological tolerance and block T cell-mediated immune responses at the end of the response window.

B Cells

Memory B cells carry the memory of previous exposure to antigen.
They are generated after exposure to antigen by cytokine signaling.
Plasma B cells are long-lived, non-proliferating antibody-secreting cells.
They arise after exposure to antigen.

Positive and Negative Selection of Lymphocytes

Positive selection ensures lymphocytes are able to respond to antigen.
Negative selection removes lymphocytes that bind strongly to self antigens.

Outcomes of Negative Selection of Lymphocytes

Receptor editing changes the lymphocyte receptor so it no longer recognizes self antigens.
Anergy changes the lymphocyte so it is no longer capable of an immune response.
Apoptosis (clonal deletion) results in cell death.
Ignorance occurs when the lymphocytes continue to bind self antigens without causing an immune response.

Overall Flow of Innate Immunity

The innate immune system recognizes common pathogen-associated molecular patterns (PAMPs) and uses nonspecific mechanisms to destroy invaders.

Physical Barriers: The Skin

The skin is the first line of defense against foreign threats.
The epidermis is waterproof and chemically resistant to bacterial enzymes.
Glands maintain a surface pH of 3-5, blocking the growth of most microorganisms.
Mucosal membranes contain anti-pathogenic substances.

Cytokines

Cytokines act in an autocrine, paracrine, and endocrine manner.
They are produced by a broad range of immune cells.
Overproduction of cytokines can lead to sickness and death.

Granulocytes and Mast Cells

Neutrophils are the most abundant leukocyte and are the first responders to infection.
They release anti-microbial enzymes and "NETS."
Basophils comprise ~1% of leukocytes.
They release histamine at the site of infection.
They are responsible for the symptoms of allergies.
Mast cells comprise ~6% of leukocytes.
They release histamine, heparin, and other compounds.
They are also responsible for the symptoms of allergies.
Eosinophils comprise ~6% of leukocytes.
They release histamine.
They are highly effective against parasites.

NK Cells

NK cells induce apoptosis in virus-infected and cancer cells.
They release granules containing proteases and perforin.
They also secrete ɑ-defensins (anti-microbial peptides).
Individuals with impaired NK cell development display a heightened incidence of blood cancer.

Macrophages

Macrophages engulf foreign threats through phagocytosis.
Macrophages are drawn to the site of infection by chemotaxis.
They extend pseudopodia around foreign threats and internalize them within a vesicle (phagosome).
The phagosome fuses with lysosomes, which contain proteases and toxic chemicals to kill foreign threats.

Complement System

Complement is a family of over 30 soluble and cell-bound proteins.
Most components are produced in the liver in inactive forms.
Three separate pathways converge to produce C3 and C5 convertase activities.

The Membrane Attack Complex (MAC)

The MAC opens pores on target cells.
It is formed by the complement system.

Inflammation

Inflammation is a stereotypic innate immune response.
It is characterized by redness, heat, swelling, and pain.
It is triggered by the release of inflammatory mediators, such as histamine.

Adaptive Immunity

Adaptive immunity is a specific and highly targeted immune response that adapts to recognize and eliminate specific pathogens.

A Comparison of Innate and Adaptive Immunity

Innate immunity is nonspecific and responds rapidly to infection, whereas adaptive immunity is specific and requires time to develop.
Innate immunity does not have memory, meaning the response time stays the same for each infection, but adaptive immunity has memory, meaning the response is faster with repeated exposure to an antigen.

Antibody-Mediated Immunity and Cell-Mediated Immunity

Antibody-mediated immunity is a type of adaptive immunity in which B lymphocytes produce antibodies that target specific antigens.
Cell-mediated immunity is a type of adaptive immunity in which cytotoxic T lymphocytes directly attack and destroy infected or cancerous cells.

Antigens

Antigens trigger an adaptive immune response.
The immune system recognizes epitopes, which are discrete sites on macromolecules.
Any molecule has the potential to act as an antigen, but some are more potent than others.
Proteins tend to be the most potent antigens.

Antibody Structure

Antibody structure has a variable region and a constant region.
The variable region recognizes and binds to antigens.
The constant region determines the antibody's isotype and effector function.
Each chain has a heavy polypeptide chain and a light polypeptide chain.
The constant region for the heavy chain determines the isotype of the antibody.

Antibody Isotypes

IgM is the first antibody produced upon initial antigen exposure.
IgD is expressed on the surface of naive B cells and acts as an antigen receptor.
IgG is the most abundant antibody class in serum, crosses the placenta, and protects the fetus.
IgA is the main antibody class in secretions such as breast milk, saliva, and tears.
IgE mediates allergic and parasitic responses by binding to mast cells and basophils.

Functions of Antibodies

Antibodies neutralize antigens by blocking their function.
Antibodies agglutinate antigens into larger complexes, making them more easily recognized by macrophages.
Antibodies precipitate antigens out of solution, also making them easier for macrophages to recognize.
Antibodies activate complement through the Fc region, leading to cell lysis and attraction of other leukocytes.
Antibodies recruit and activate lymphocytes.

How Antibodies Recognize So Many Antigens

Antibodies recognize a wide variety of antigens by diversifying their variable regions through a process called VDJ recombination.
Each region is made up of small gene segments with multiple copies.
These gene segments recombine in a random fashion, generating many possibilities.
Other modifications are also made (removal of bases from ends, addition of extra bases) to further increase variability.

MHC Types and Structures

Major Histocompatibility Complex (MHC) molecules present antigens to T cells.
MHC I presents antigens that originate from inside the cell to cytotoxic T cells.
MHC II presents antigens that originate outside the cell to helper T cells.
Individuals inherit one copy of each MHC gene from each parent, making each individual's MHC unique.
MHC is a critical means through which cells communicate about self versus non-self.

Antigen Presentation on APCs

Antigen-presenting cells (APCs) internalize, process, and present antigens to T cells.
APCs include macrophages, B cells, and dendritic cells.
MHC I presents peptides from the cytosol.
MHC II presents peptides from endocytotic vesicles.

Steps of Humoral-Mediated Immunity and Antibody Production

Humoral-mediated immunity involves the production of antibodies by B cells.
The steps involve antigen recognition, activation of B cells, and antibody production.

Primary vs. Secondary Antibody Responses

The primary antibody response is the initial immune response to a new antigen.
The secondary antibody response is the subsequent immune response to the same antigen, which is faster and more robust due to the presence of memory B cells.
Antibodies are more rapidly produced in the secondary response.
The primary response starts with IgM, while the secondary response starts with IgG.

Cell-Mediated Immunity: Activation of Cytotoxic T Cells

Cell-mediated immunity involves direct destruction of infected or cancerous cells by cytotoxic T cells (TC).
TC cells require activation by helper T cells (TH) to attack infected cells.

Cell-Mediated Immunity: Activation of Helper T Cells

Helper T cells are activated by antigen-presenting cells (APCs).
TH cells release cytokines that help activate cytotoxic T cells (TC) to kill infected cells and B cells to produce antibodies.

Autoimmune Diseases

Autoimmune diseases are caused by the immune system attacking the body's own tissues.
They can be caused by molecular mimicry or a deficiency in regulatory T cells.
Treatments include immunosuppressive drugs, removal of the thymus, and plasmapheresis.

Aging and the Immune System

The immune system declines in function as we age.
Tissues and organs related to immunity decrease in size and become less responsive to pathogens.
Elderly individuals are more likely to have to take immunosuppressive drugs for other conditions.
They produce fewer antibodies and memory B cells, reducing vaccine effectiveness.
They also accumulate damage caused by autoimmune diseases that developed earlier in life.

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