Chapters 14-15 - The Immune System

Lymphatic System

Involved in both innate and adaptive immunity; Consists of a branching network packed with white blood cells that fight infections

Lymphatic Vessels

collect fluid from body tissues and return it

Lymph Nodes

round organs packed with macrophages and lymphocytes

Lymph

fluid that surrounds body cells

Antigen

any substance that produces an immune system response, in particular antibody production

Epitope

Site on antigen that reacts with specific antibody

Valence

umber of epitopes on an antigen

Antibody Affinity

Strength of bond between antibody and given antigen-
binding site

Avidity of an antibody

Overall ability to bind antigen at all antigen-binding sites

True or false; an antigen is always pathogenic or foreign.

False

Innate Immunity

non-specific defenses; plays an important role shortly after pathogen infection; Fast reaction; Same for all individuals; Occurs for every single pathogen regardless of the species, type of microbe, or virus

First Line of Defense

non-cellular; can include mechanical (physical) barriers or chemical barriers

Physical barriers of the innate immune system

can be living or non-living; examples include tree bark and eggs shells

Mechanical immunity

Form protective covering bathed in antimicrobial peptides; Trapping of microbes by mucus and phagocytes in mucosal tract

Chemical barriers in innate immunity

From skin and mucous membranes; Sebaceous secretions; Antimicrobial secretions from specialized glands (meibomian glands)

Chemical defenses present in tears, saliva, and skin

lysozymes and defenses; High lactic acid and electrolyte concentration in sweat; Skin’s acidic pH

Lysozymes

chemical innate immunity; an enzyme that hydrolyzes the cell wall of bacteria

Defensins

Chemical innate immunity; peptides that lyse bacteria and fungi

Second Line of Defense

cellular; includes Inflammatory response, Interferons, Phagocytosis, and Complement

Inflammatory Response

cell generates inflammation (recruitment of blood cells) in response to trauma; Nonspecific response to tissue injury; Can be caused by pathogen or physical trauma; Disinfects tissues and limits further infection

Acute Inflammation

Localized is the immediate response of body to injury or cell death

Systemic inflammatory responses

Release of additional neutrophils from the bone marrow; Fever triggered by substances released by macrophages & pathogens

Mast cells release ________ for inflammatory responses

histamines

Major evens in a local inflammatory response

1. mast cells release histamines; capillaries dilate

2. Neutrophils and anti-microbial peptides enter the tissue

3. Neutrophils digest pathogens and cell debris; tissue heals

Systemic Inflammation

fever; change in the homeostatic set point

Benefits of fever

Inhibits multiplication of temperature-sensitive microorganisms; Impedes nutrition of bacteria by reducing the available iron; Increases metabolism and stimulates immune reactions and protective physiological processes

Complications of fever

Simultaneous signaling to increase temperature and return to set point (Ex:Vasoconstriction and Vasodilation simultaneously stimulated); Results in Hypotension and in rare cases Multiple Organ Dysfunction and Death

Interferons

Cytokines (signaling proteins) made and released by host cells in
response to the presence of viruses; Causes nearby cells to heighten their anti-viral defenses; does not help the cell releasing them, but helps neighboring cells

True or false: interferons only occur in response to viruses.

True

Neutrophils

the first cells to respond to infection

Macrophages

immune cells that patrol the body

Dendritic Cells

part of the natural defenses found in the skin and mucous membranes

Natural Killer Cells

do not recognize foreign cells, but instead recognize and kill
host cells that are infected by a virus or have become cancerous or otherwise abnormal

Mast Cells

release histamine, a contributor to allergic reactions and inflammation

Eosinophils and basophils

defend against parasitic infections, & contribute to allergies

Immune cells that engulf pathogens and break apart via hydrolytic enzymes

Neutrophils, Macrophages, and Dendritic Cells

Microbial Recognition

Body defense cells contain pattern-recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs)

True or False: Neutrophils die in the process of engulfment and digestion.

True

True or False: Macrophages & Dendritic Cells - are Antigen Presenting Cells (APCs).

True

What kind of cells are the bridge between the innate and adaptive immune system?

Antigen presenting cells (APCs)

Major Histocompatibility Complex (MHC)

Genes that code for self/non-self recognition; three classes

Class I MHC

found on all types of nucleated cells— important for organ transplantation - binds to antigen peptides that originate in the cytoplasm and presents antigen to CD8+ T cells

Class II MHC

found only on cells that can process and present antigens to T lymphocytes—macrophages, dendritic cells, and B cells - binds to antigen fragments that come from outside the cell and present to CD4+ T-helper cells

Class III MHC

molecules include secreted proteins not required for self/non-self recognition

Natural Killer (NK) Cells

Once activated, release pore-forming proteins called perforins, granzymes (proteases), and chemokines; End result is death of target cell

What kinds of cells do NK cells recognize?

Cells that undergo a declined expression of MHC I molecules, cells that contain surface antigens displayed by some tumor cells, or virally infected cells

The Complement System

Consists of more than 30 different inactive heat, labile serum, and membrane-bound glycoproteins that act in sequence; One complement protein activates another

What is the response of activation of the complement system?

sets off a biochemical cascade to amplify the immune response in 3 ways: Penetrate microbial cell membranes, causing cell lysis - formation of a membrane attack complex (MAC), Promoting phagocytosis through opsonization, Promoting the recruitment of white blood cells through inflammation

Opsonization Process

Process in which microbes are coated by serum components (opsonins) or the process in which microbes are coated by antibodies; Results in the recognition/ingestion by phagocytic cells;

Opsonization steps

opsonin attaches to a pathogen, slows them down, and increases the likelihood of phagocytosis; attaches loosely and non-specificly

True or false: opsonization can stop further infections.

False

What is the primary function of mast cells?

releases signals that increase blood flow to the wound area

What is the primary function of neutrophils?

kills invading cells via phagocytosis

What is the primary function of macrophages

releases cytokines that recruit other cells to the wound site and stimulates a variety of activities kills invading cells via phagocytosis

What is the primary function of dendritic cells?

Capture antigens and other foreign debris by macropinocytosis, phagocytosis, and receptor-mediated endocytosis; Connects innate and adaptive immune responses by activating certain cells of the adaptive immune response

What molecule is produced by mast cells?

Histamine

What molecule is procured in response to injured tissues and by macrophages in tissues?

Chemokines

Which cell produces cytokines other than chemokines?

Macrophages

What are histamines received by?

blood vessels

What are chemokines received by?

Neutrophils and macrophages

What are cytokines other than chemokines received by?

white blood cells, bone marrow, CNS, and local tissues

What is the message/function of histamines?

High concentration dilates blood vessels near wound site, among other activities

What is the message/function of chemokines?

Marks the path to wound; promote dilation and increased permeability of blood vessels

What is the message/function of cytokines other than chemokines?

Marks the path to wound; Increase production of macrophages and neutrophils; Induces fever by raising set point for body temperature
Stimulates cells involved in wound repair

Third Line of Defense

includes B and T lymphocytes, antibodies, cytotoxicity

How long does specific immunity reponses (either adapted or acquired immunity) require before induced or effective clearing of pathogens?

Days to weeks during the first infection

True or false: Specific immune responses are activated only after exposure to antigens.

True

True or false: specific immune response (adapted or acquired immunity) differs from individual to individual dependent on
previous exposures over individuals’ lifetime.

True

Adaptive Immunity Characteristics

1. Discrimination between self and non-self

2. Responds to non-self

3. Specificity - Can be directed towards specific pathogens

4. Diversity - Generates enormous diversity of cellular receptors and antibodies

5. Memory -Response to a second exposure to a pathogen is so fast that there is usually no noticeable illness

What are the types of acquired immunity?

natural immunity and artificial immunity

Natural Immunity

acquired through normal life experiences and is not induced through medical means

Active Immunity

retains immune memory forever; is the result of a person developing his or her own immune response

Passive immunity

does not retain immune memory forever; occurs as a consequence of one person receiving preformed immunity made by another person

What is an example of natural active immunity?

Infection (antibody production)

What is an example of natural passive immunity?

maternal antibodies

Artificial immunity

produced purposefully through medical procedures; also called immunization

What is an example of artificial active immunity?

vaccination

What is an example of artificial passive immunity?

immune globulin therapy

What are the two types of antibody response?

primary immune response and secondary immune response

Primary immune response

first exposure, develop memory cells for infecting pathogen

Secondary immune response

memory cells initiate a faster, stronger, and more prolonged response to the pathogen; more effective due to B and T cells; More effective for memory of past exposure

Why is the primary immune response more time consuming than the secondary immune response?

clonal selection/generating the right fit

What are the steps of primary immune response to an infection?

1. Recognition

2. Clonal selection

3. Effector cells attack

4. Memory Cells remember

Recognition (primary immune response)

a lymphocyte comes into contact with the antigen specific to its receptor and the cell initiates a response that leads to the destruction of the antigen

Clonal Selection (primary immune response)

the lymphocyte divides numerous times, creating two populations of cells with the same antigen specificity

Effector Cells attack (primary immune response)

effector cells immediately take action, leading to the destruction of the antigen

Memory Cells remember (primary immune response)

memory cells remember the antigen so that if the body is infected with the same antigen in the future, they will be ready to respond

Clonal Selection Theory

Undifferentiated lymphocytes in embryo and fetus undergo a continuous series of divisions and genetic changes that generate millions of different cell types, each with a particular/unique receptor
specificity

Where do lymphocytes originate?

the bone marrow

Where do B cells fully develop?

the bone marrow (humoral immunity)

Where do T cells develop?

in the thymus - cellular immunity

Endless variation in antigen receptors allows lymphocytes to _______

recognize billions of different pathogens

What are the subtypes of T cells?

Helper T cells (T_H or CD4) and cytotoxic T cells (T_c or CD8)

Helper T cells (T_H or CD4)

upon activation can activate cytotoxic T-cells or B cells

Cytotoxic T cells (T_c or CD8)

destroy cells that contain the same antigen presented during initial activation

True or false: cytotoxic T cells can detect antigens on their own.

False

What is essential for the acquired immune system to recognize foreign molecules?

Activation of acquired immune cells

Antigen Presenting Cells (APCs)

present bound pathogen/foreign particles to naïve helper T cells via MHCs by moving them to surface of cell

How to MHCs activate naive helper T-cells?

by binding to the TCR of the TH - Correct Binding ensures the specificity to the Pathogen (correct key and lock)

What does binding of MHCs to the t-cell receptor do?

stimulates division and replication so more activated TH cells with the TCR which binds to the antigen are present in body