Functional Organization of the Immune System

Type IV reactions:

"cell-mediated reactions" Occur when antigens trigger helper T cells (TH), which in turn activate cytokines, macrophages, and cytotoxic T cells. Are often caused by intracellular pathogens and are accompanied by inflammation. i.e. (systemic inflammatory response syndrome (SIRS))

The 5 following factors determine the likelihood of a pathogen causing disease in the animal:

1 - Exposure: exposure to a pathogen. 2 - Mode of infection/transmission: Aerosol transmission = more likely Direct contact = less likely 3 - Virulence: the relative strength of the pathogen. 4 - Immune system strength: The immune systems of young, old, or immunosuppressed animals are usually not functioning at 100% capability. 5 - Resistance: The immune system has been primed, through memory cell production, to fight the pathogen, making it less likely to result in disease. (natural exposure/vaccination = acquired resistance)

In an adult animal, B cells and T cells exist in at least three different stages of differentiation:

1 - Naive cells have entered the lymphatic system, but have not encountered an antigen. 2 - Cytotoxic (effector cells) have been activated and are involved in eliminating a pathogenic antigen. 3 - Memory cells are the survivors of past infections, capable of providing long-term immunity.

In sensitized animals, allergic reactions can become even more severe, resulting in hypersensitivity reactions, which are classified into four types:

1 - Type I reactions: are generally severe and can include anaphylactic shock (hives, edema, excess salivation, vomiting, diarrhea, shock, and death). 2 - Type II reactions: occur when infection is present, antibodies are being produced, and the complement system is activated. 3 - Type III reactions: occur when an antibody and an antigen bind and form an immune complex. 4 - Type IV reactions: Type IV or cell-mediated reactions occur when antigens trigger helper T cells (TH)

What is the function of Pathogen-associated molecular patterns (PAMPs) and where are they found?

1 - help the innate immune system recognize pathogens 2 - are found on the membrane surface of invading pathogens

Phagocytosis includes five steps

1. ACTIVATION & CHEMOTAXIS: Phagocytes are stimulated by inflammatory signals to begin moving toward the "nonself" cell (bacterium). 2. ATTACHMENT: Receptors on the phagocytes recognize the nonspecific components on the pathogen cell membrane and bind to them. 3. INGESTION OR ENDOCYTOSIS: The attached phagocyte extends projections from its plasma membrane, called pseudopods. Pseudopods engulf the microorganism into a vesicle called a phagosome. 4. DESTRUCTION: A lysosome fuses with the phagosome, creating a phagolysosome. The lysosome releases digestive enzymes into the phagolysosome. The enzymes break down the bacteria. 5. EXOCYTOSIS: The phagolysosome releases the indigestible material from the phagocyte.

IgM is a temporary antibody that disappears within...

2 or 3 weeks after the initial infection and is replaced by the IgG antibody.

phagocytosis

A type of endocytosis in which a cell engulfs large particles or whole cells "cell eating"

Type I reactions:

Are generally severe and can include anaphylactic shock (hives, edema, excess salivation, vomiting, diarrhea, shock, and death). Atopy (atopic dermatitis), flea allergy dermatitis, and food allergies Without immediate medical intervention, these reactions can quickly become fatal.

How do B lymphocytes react to pathogens?

B cells do not directly destroy pathogens. Each B cell is programmed to secrete a specific antibody (also known as immunoglobulin or Ig) that will lead to phagocytosis and destruction of the pathogen.

humoral immunity

B cells produce antibodies after exposure to specific antigens; type of adaptive immunity Block infections and eliminate extracellular microbes

Cat Bite Wound

Cat bite wounds are especially contaminated and infection is almost guaranteed. Upon penetration of the its teeth through the skin of a person or another animal, bacteria are deposited deep into the wound

The innate immune system consists of a collection of multiple subsystems. They can be divided into the CELLS that largely eat and kill invaders and the MOLECULES that bind and kill the invaders. List several functions of each:

Cells - detect invaders, eat invaders, kill invaders, kill virus-infected cells Molecules - bind & kill invaders, coat invaders so cells can kill them, block microbial growth, prevent microbial spread, mobilize body defenses.

What are some functions of Cytokines

Cytokines are communicators. They provide communication between leukocytes and other cells and among leukocytes themselves. They are signaling proteins that are secreted by certain cells in the body Often their role is to mediate the immune or inflammatory response by attracting immune cells to a specific site: the site of infection, inflammation, or trauma.

What are the first and second line of defense?

First Line of Defense - external innate immunity Second Line of Defense - internal innate immunity

Interferons (IFNs)

Interferons (IFNs) are proteins produced by an animal's immune system cells in response to the presence of viruses, bacteria, cancer, and other foreign invaders.

Name 3 types of cytokines

Interleukins, interferons, and chemokines

Killed virus vaccine

Killed virus vaccines contain virus particles that are inactive. Once killed, the viruses are unable to revert to their disease-causing state, but the immune system is still able to recognize the remnants of the virus and respond appropriately.

Where do B Lymphocytes originate?

Like all blood cells, B lymphocytes (B cells) originate in the red bone marrow.

When T cells and B cells are activated in an immune response, they produce clones, which are the...

Memory cells. These clones stay in the lymph nodes or circulate in blood, looking for the same antigen that originally triggered the activation of their parent cell. Should that antigen enter the animal again, memory cells will initiate an immune response stronger and faster than the initial immune response, hopefully preventing the animal from getting sick.

Modified live vaccine

Modified live vaccines contain live-virus particles that have been weakened (attenuated) so they are nonpathogenic but still recognized by the animal as antigenic. Produces a strong immune response because they mimic a natural infection.

Type III reactions:

Occur when an antibody and an antigen bind and form an immune complex. These immune complexes are insoluble and become trapped in the basement membrane of small blood vessels in tissues (joints, kidneys, lungs, brain, and skin). This typically produces acute inflammation and damage to affected tissues. Type III reactions are some of the most common immunologic diseases. i.e. (systemic lupus erythematosus, hypersensitivity pneumonitis, and vasculitis)

Type II reactions:

Occur when infection is present, antibodies are being produced, and the complement system is activated. This reaction occurs when reactive antibodies destroy the body's own cells. This leads to diseases where the immune system is the cause of disease rather than the cure.

Antigen VS Pathogen

Pathogens are microbes that can infect the body and cause illness. Antigens are parts of the pathogen that alert the body to an infection. Immune cells can recognize antigens to target and remove a pathogen from the body, thereby stopping or even preventing an illness.

Passive Immunity

Receiving antibodies from an external source can also protect the animal but its immune system is not actively involved.

Why are B cells most effective in providing immunity against extracellular pathogens?

Since the antibodies that are produced by the B cells are circulating in blood, lymph, and tissue fluid, they are most effective in providing immunity against extracellular pathogens.

Innate Immune System

The innate immune system is rapid, nonspecific and destroys "nonself" invaders indiscriminately. It is present at birth and uses physical, chemical, and cellular components to protect the body from anything identified as "nonself." The innate immune system is unable to target specific organisms; instead, it destroys all "nonself" invading organisms by the same mechanisms.

What is the function of Pattern Recognition Receptors (PRRs)

The membrane surface of a macrophage or dendritic cell has receptors called pattern-recognition receptors (PRRs) that fit the PAMP on the pathogen's cell membrane.

Name the anatomic barriers that include structures on the surface of the body that prevent disease - (external innate immunity)

The skin, the largest organ in the body, has a thick layer of keratinized epithelial tissue that is impermeable to a majority of pathogens. Mucous membranes of the epithelium that line the respiratory, digestive, urinary, and reproductive systems also have unique structures that provide innate immunity. Tears, saliva, and nasal discharge production create a flushing action that helps prevent infection in the eyes, mouth, and nose

Helper T cells (Th cells)

These are the most numerous T cells. They help the immune response by secreting cytokines into the surrounding tissue.

Cytotoxic T cells (Tc cells)

These cells are also known as effector cells, killer cells, or killer T cells. They attach to antigenic markers and destroy the cells to which they are attached. However, they are not damaged themselves.

Regulatory T cells (Ts cells)

These cells inhibit helper T cell and cytotoxic T cell function by negative feedback. They also prevent B cells from transforming into plasma cells.

T Lymphocytes originate in...

These cells originate in the red bone marrow and migrate to the thymus where they mature, multiply, and enter the bloodstream as T cells.

Describe the function of Chemokines

They stimulate the movement of leukocytes from blood into tissue and toward an injury/inflammatory site where there are high concentrations of the chemokines.

complement cascade

a precise sequence of events, usually triggered by antigen-antibody complexes, in which each component of the complement system is activated in turn

Disseminated intravascular coagulation (DIC)

abnormal blood clotting in small vessels throughout the body that lead to multi organ failure - resulting in damage to body organs

IgM antibodies are produced when... (immunoglobulins)

an animal is first exposed to an antigen are the largest antibody

IgG antibodies are involved in fighting...

bacterial and viral infections.

IgE antibodies

binds to allergens and triggers histamine release from mast cells and basophils. It also protects against some parasitic helminth (worm) infections

Natural Killer (NK) cells are found in the...

blood and lymph are also a part of both the innate immune system and the adaptive immune system.

Immunoglobulins (IgM) are found in...

blood and lymph fluid are the first immunoglobulin made by newborn animals.

Phagocytosis is one way the body can remove pathogens in the...

blood, fluids, and body tissues.

lysosome

cellular organelle that contains digestive enzymes to help break down bacteria

Elevated IgG levels can indicate a...

chronic infection in an animal

opsonization

coating the antigen with complement proteins to make it more visible to the phagocyte

Phagocytes contain receptors on their outer membrane that help...

differentiate cells as being "self" versus "nonself."

IgD antibodies

has been shown to activate basophils and mast cells but its exact mechanism is unknown.

The adaptive immune system can be divided into two distinct types of immunity:

humoral and cell-mediated

NK Cells are able to...

identify and kill virus-infected cells, stressed cells, and tumor cells

The immune system is functionally divided into two categories...

innate and adaptive immunity

Interleukins control what 3 things during an immune response?

leukocyte (especially T and B cells) growth, differentiation, and activation during an immune response

It was initially thought that interleukins were produced by...

leukocytes and acted on only leukocytes, which is how they got their name. Since that time other cells have been shown to produce interleukins.

abcess

localized collection of pus - at the site of an infection

The innate immune system does not recognize specific pathogens, rather...

macrophages recognize common structures shared by large groups of pathogens

The most common method of providing passive immunity is through...

maternal antibodies that are passed from mother to the fetus through the placenta (transplacentally), or to the neonate via colostrum (the antibody-rich milk the mother produces right before and after birth).

There are two primary types of vaccine used in veterinary medicine today:

modified live and killed virus.

The most common phagocytic cells are the...

neutrophils, monocytes, macrophages, and dendritic cells.

Complement proteins are produced primarily...

primarily in the liver and circulate in the blood in their inactive form.

IgA antibodies

protect body surfaces from foreign substances. These antibodies play an important role in preventing diseases caused by antigens that may enter the body through mucosal surfaces (e.g., intestinal tract and lungs). Intranasal applications, such as those used in intranasal vaccination, create this type of antibody.

The complement system

proteins in the blood that help antibodies kill their target

The four cardinal signs of inflammation are:

redness, swelling, heat, and pain

Unlike the innate immune system, which eliminates anything identified as nonself, the adaptive or acquired immune system is...

slower to respond, is specific, and has memory It targets pathogens with precision.

killed virus vaccines are weaker than when modified live vaccines are used so...

so multiple doses must be administered before immunity is achieved.

Adaptive Immune System

targets specific organisms, but it is slower to respond to an invading organism. It is not present at birth but develops and adapts as the animal matures and is exposed to a variety of antigens. Once an animal is exposed to an antigen, the adaptive immune system uses antibodies, memory cells, plasma cells, B lymphocytes, and T lymphocytes provide immunity.

Plasma cells are responsible for...

the actual production, storage, and release of antibodies.

All NK cells have two types of receptor on their cell membranes to help determine which cells to kill "non-self" or not to kill "self"

the killer-activating receptor (KAR) and the killer inhibitory receptor (KIR).

Once created, plasma cells remain in...

the lymph nodes and spleen

IgG antibodies

the smallest but most common antibody. It is produced and released by plasma cells and found in blood and extracellular fluid when the animal has been exposed to an antigen for an extended time.

paracrine

they act on cells near the cell that secreted them

autocrine

they act on the cell that secreted them

NK Cells differ from phagocytes in that they do not...

they do not ingest the target cell. Instead, they bind to the cell and induce cellular changes that lead to apoptosis (programmed cell death) before the virus can mature

endocrine

they travel to other parts of the body and act on cells in that location

The precursor cells of T lymphocytes (T cells) are...

thymocytes

The adaptive immune system also has the ability to remember...

to remember pathogens that have infected the organism and destroy them before they can cause disease in an animal a second time.

Inflammation is the body's localized reaction created by the innate immune system in response to...

trauma, infection, chemical exposure, or excessive heat.

Once a pathogen has made its way past the physical barriers of the innate immune system, the body...

tries to control the spread of the infection through acute inflammation.

The two most important functions of the complement system are to...

trigger inflammation and to alter microbial cell membranes Either way, it hastens the elimination of microbial invaders and is thus a key component of the innate immune system

Cell Mediated Immunity

type of immunity produced by T cells that attack infected or abnormal body cells Kill infected cells and eliminate reservoirs of infection