CB 35 The Immune System

Describe e killing action of cytotoxic T cells on an infected host cells

1 An activated cytotoxic T cell binds to a class 1 MHC antigen fragment complex on an infected cell via its antigen receptor and an accessory protein called CD8. 2 The T cell releases perforin molecules which form pores in the infected cell membrane and granzymes which break down proteins. Granzymes enter the infected cell by endocytosis 3. The granzymes initiate apoptosis within the infected cell leading to fragmentation of the nucleus and cytoplasm and eventual cell death. The released cytotoxic T cell can attack other infected cells.

Explain the major events in a local inflammatory response

1 mast cells release histamines and macrophages release cytokines. These signalling molecules cause nearby capillaries to dialate. Capillaries become more permeable allowing fluid containing antimicrobial peptides to enter the tissues. The signals released by the immune cells attract neutrophils. 3 neutrophils digest cell debris sat atheist site and the tissue heals.

How do cytotoxic T cells interact with infected cells

1. An activated cytotoxic T cells binds to a class 1 MHC antigen fragment complex on an infected cell via its antigen receptor and accessory protein called CD8. The T cell releases perforin molecules which form pores in the infected cell membrane and granzymes which break down proteins. granzymes then enter the infected cell by endocytosis. 3. the granzymes start apoptosis whiten the infected cell and lead to fragmentation of the nucleus and cytoplasm and eventual cell death. The released cytotoxic T cell can attack other infected cells.

The antigen presenting cell can be

A dendritic cell, macrophage or B cell

Define infection- complement system

A group of about 30 blood proteins in blood plasma that may amplify the inflammatory response, enhance phagocytosis, or directly Lyse extracellular pathogens

A helper T cell triggers what responses

A humoral response and a cell mediated response

Molecular recognition in innate immunity relies on what

A mall set of receptors that bind to molecules or structures that are absent from animal bodies but common to viruses, bacteria or microbes. Also this is a rapid response.

Define toll like receptor

A membrane receptor on a phagocytic white blood cell that recognizes fragments common to a set of pathogens

Define. Cytotoxic T cell

A type of lymphocyte that when activated kills infected cells as wells as certain cancer cells and transplant cells and it uses proteins to kill them.

Molecular recognition in adaptive immunity relies on what

A vast Arsenal of receptors each of which recognizes a feature typical of a particular molecule in a particular pathogen. Also this is a slow response.

Explain the cycles of signaling and response that transform the site during inflammation

Activated complement proteins promote further release of histamine, attracting more phagocytic cells that enter injured tissues and thus carry out additional phagocytosis. Simultaneously, enhanced blood flow to the site helps deliver antimicrobial peptides. The result is an accumulation of pus, a fluid rich in white blood cells, dead pathogens and cell debris from damaged tissues.

On what organism is innate immunity found in

All animals

On what organisms is adaptive immunity found in

All vertebrates

Define secondary immune response

An adaptive immune response elicited on a second or subsequent exposures to the same pathogen. This response is more rapid and of greater magnitude.

Define immune system

An animal's body system of defences against disease causing agents

Explain the swelling response

An innate immune defense that starts off with you feeling pain and seeing the infected part swollen which are the result of a local inflammatory response. One important signaling molecule is histamine which is stored by mast cells and serve to trigger nearby blood vessels to dilate and become more permeable. Another signaling molecule is cytokines which are discharged by activated macrophils and neutrophils and that serve to promote blood flow to the site of injury.

Define pathogen

An organism or virus that causes disease

What is the difference in antibodies and B cell antigen receptors

Antibodies are secreted rather than membrane bound.

What are the humoral responses of adaptive immunity?

Antibodies defend against infection in bodily fluids

Describe the steps in B cell activation

Antigen binds to a B cell antigen receptor. The cells secrete a soluble form of the receptor and this secreted proteins is called an antibody or immunoglobin.

Describe he complex interaction between the helper T cell and the antigen presenting cell

Antigen receptors on the surface of T cells bind to an antigen fragment and to the class 2 MHC molecule displaying the fragment on the antigen presenting cell. Simultaneously an accessory protein called CD4 on the helper T cell binds to the class 2MHC molecule helping keep the two cells joined. As the two cells interact signals in the form of cytokines are released.

The major class of defense molecules in invertebrates consists of what

Antimicrobial peptides which circulate throughout the body and inactivate or kill fungi and bacteria by disrupting their plasma membranes

Define eosinophils cells

Are often found beneath mucous membranes which are important in defending against multicellular invaders like parasites, eosinophils then discharge destructive enzymes.

Suppose humans were the major host for a bacterial species. What temperature would you predict would be optimal for growth of this species?

At normal human body temperature or if fever were induced then at a temperature a few degrees higher

What innate defenses are found among invertebrates and vertebrates

Barrier defenses phagocytosis and anti microbial peptide

What causes swelling?

Blood engorged capillaries that leak fluids into neighboring tissues

What distinguishes a host cell from an antigen presenting cells

Body cells have class 1MHC molecules and antigen presenting cells have both class 1and 2MHC molecules.

Define killer cells

Cells that circulate through the body and detect the abnormal array of surface protein characteristic of some virus infected and cancerous cells. After detection, they release chemicals that lead to cell death, inhibiting further spread of the virus or cancer.

Explain septic shock

Condition that derives from certain bacterial infections that induce this systemic inflammatory response. High fever, low blood pressure and low blood flow through capillaries characterises this condition.

What are the cell-mediated responses of adaptive immunity?

Cytotoxic cells defend against infections in body cells

Explain how antimicrobial peptides work

Damage broad groups of pathogens by disrupting membrane integrity

TLR3 recognizes what?TLR4 ? TLR5?

Double stranded RNA a form of nuclei acid characteristic of certain viruses; recognizes lyposaccharide a molecule found on the surface of many bacteria and TLR5 recognizes flagellin the main protein of bacterial flagella

Insects in terrestrial and freshwater habitats rely on what as their first line of defence against infection

Exoskeletons

T or F. A foreign molecule has to be pathogenic to elicit an immune response

False

What two requirements must be met for a helper T cell to activate adaptive immune responses

First a foreign molecule must be present that can bind specifically to the antigen receptor of the T cell.Second, this antigen must be present on the surface of an antigen presenting cell

How do we generate such remarkable diversity in antigen receptors

For example lets consider the light chain of an antibody gene. A receptor light chain is encoded by three segments: a variable, a joining and a constant segment. The V and J encode the variable region of the receptor chain and the c encodes for the constant. The light chain gene contains alternative copies of the v and j segments which are arranged in a series. The pieces can then be combined in two hundred different ways. To rearrange the DNA an enzyme complex called recombinase links a v gene segment to a j gene segment. then the J and C segments of the RNA transcript will be joined when splicing removes the intervening RNA. In any cell only one allele of a light-chain gene and one-allele of a heavy chain gene are rearranged. Also, the rearrangement are permanent and are passed on to daughter cells when the lymphocyte divides.

How do host cells display that they are infected?

Fragments of foreign proteins produced in host cells associate with class 1 MHC molecules and are displayed on the host cells which are then recognized by cytotoxic T cells.

Describe the structure of an antigen receptor on a B or T cell

Has 4 polypeptide chains: 2 heavy chains and two light and disulfide bridges link the two together. A transmembrane region near the end of the heavy chains anchors the receptors in the plasma membrane. The light and heavy chains have a constant region that vary little among receptors on different B cells. Then the variable region on each chain varies extensively from one B cell to another. Together the heavy chain and the light chain form an asymmetric binding site for an antigen. Each antigen receptor has two identical antigen-binding sites.

The secondary immune response relies on what

He reservoir of T and B memory cells generated following initial exposure to an antigen

Give an examples of phagocytic cells in insects

Hemocytes travel through the body in the hemolymph, the insect circulatory fluid. Some hemocytes ingest and break down bacteria and other substances(phagocytosis) while others release chemicals that kill pathogens and help entrap large invaders.

What if both copies of a light chain gene and a heavy chain gene recombined in each B cell how would this affect B cell development and function?

If each B cell produced 2 different light and heavy chains for its antigen receptor different combinations would make four different receptors and if any one of those was self reactive would be eliminated in the generation of self tolerance. For this reason many more B cells would be eliminated and those that could respond to a foreign antigen would be less effective at doing so due to the variety of receptors they express.

What interacts to destroy pathogens

Immune cells in the body fluids and tissues of most animals

How does the immune system distinguish nonself from self

Immune cells produce receptor molecules that bind specifically to ,olé uses from foreign cells or viruses and activate defence responses. This specific binding from immune receptors to foreign molecules is a type of molecular recognition.

Explain how immune cells trigger in innate immune response specific for that class

Immune cells secrete recognition proteins each of which binds to a macromolecule characteristic of a broad class of bacteria or fungi. Once bound to a macromolecule, the recognition protein triggers an innate immune response specific for that class

Dendritic cells and eosinophils provide additional functions in what?

Innate defense

On what one or two major components do animal immune systems rely on for molecular recognition and defense

Innate immunity and adaptive immunity

Explain two advantages of having memory cells when a pathogen is encountered for a second time.

It ensures that a receptor specific for a particular epitope will be present and hat there will be more lymphocytes with this specificity than in a host that had never encountered the antigen.

What function do cell-surface antigen receptors play for memory B cells?

It helps internalize the antigen

Define macrophages

Larger phagocytic cells. Some migrate and other don't. It functions by destroying microbes and in acquired immunity as an antigen presenting cell.

define active immunity

Long-lasting immunity conferred by the action of B cells and T cells and the resulting B and T memory cells specific for a pathogen. Active immunity can develop as a result of natural infection or immunization

Relate lymphocytes, thymus , t cells, B cells, antigen, antigen receptor, and epitope or antigenic determinant.

Lymphocytes are types of white blood cells on which the adaptive response relies on. They originate in the blood marrow and some migrate to the thymus and mature while others stay there and mature there. The ones that migrate to the thymus mature into T cells and the ones that stay in the bone marrow mature into B cells. The any substance that binds to T or B cells and elicits a response is an antigen via antigen receptors on T or B cells. The small accessible portion of an antigen receptor is called an epitome or antigenic determinant and this is located on the antigen which also has several different epitopes which bind to a receptor with a different specificity. Also, it is important to say that all antigen receptors produced by a single B or T cells are identical and so they bind to the same epitope. Although the antigen receptors of B and T cells have similar components they encounter antigens in different ways.

Relate lysozyme and immune system

Lysozyme a are enzymes inside the digestive system that break down bacterial cell walls and so they act as chemical barriers against pathogens ingested with food

What helps us distinguish between the primary and secondary immune responses

Measuring he concentrations of specific antibodies in blood over time

What do memory cells do if an antigen is encountered again

Memory cells specific for that antigen enable the rapid formation of clones of thousand of effector cells also specific for that antigen thus generating a greatly enhanced immune defense.

Describe 4 barrier defenses that block the entry of many pathogens

Mucous is a viscous fluid that traps microbes and other particles. Lysozomes in tears saliva and mucous secretions destroy the cells walls of susceptible bacteria as they enter the opening around the eyes or the upper respiratory tract. The stomach is acidic so microbes swallowed have to contend with that. Finally secretions from oil and sweat glands make human skin very acidic enough to prevent the growth of bacteria.

What are some unique aspects of vertebrate innate immunity

Natural killer cells, interferons and the inflammatory response

What are the 2 main types of phagocytic cells in the mammalian body

Neutrophils and macrophages

Define neutrophils

Neutrophils are the most abundant type of white blood cells that circulate in the blood, phagocytic that tend to self destruct as they destroy foreign invaders limiting their life span to a few days and are attracted to infected tissues.

In adaptive immunity receptors provide

Pathogen specific recognition

What two types of internal defenses of innate immunity do invertebrates exhibit

Phagocytic cells and anti microbial proteins

What are the internal defenses of innate immunity?

Phagocytise cells, natural killer cells, anti microbial proteins, and inflammatory response

Detection of invading pathogens triggers what in invertebrates and mammals

Phagocytosis and destruction

Define dendritic cells

Populate tissues in contact with the environment. They stimulate adaptive immunity against pathogens they engulf.

Explain how an infection-fighting complex works

Proteins that circulate throughout the body in an inactive state and are activated by substances on the surface on many microbes. Activation results in a cascade of biochemical reactions that can lead to lysis of invading cells.

Although pus is often seen as simply a sign of infection it is also an indicator of immune defenses in action. Explain

Pus contains white blood cells, fluid and cell debris And so it indicates an active and at least a partially successful inflammatory response against invading microbes.

The animal body offers what to the pathogens

Ready source of nutrients, a protected setting for growth and reproduction and a means of transport to new environments

Define Passive Immunity

Short term immunity conferred by the transfer of antibodies as occurs in the transfer of maternal antibodies to a fetus or nursing infant

What are the barrier defenses of innate immunity?

Skin, mucous membranes, and secretions

What are some adaptations that have evolved in some pathogens hat enable them to avoid destruction by phagocytic cells

Some have an outer capsule that interferes with molecular recognition and phagocytosis. Others have resist breakdown by lysosomes after being engulfed by a host cells

Explain the origin of self-tolerance

Some immature lymphocytes produce receptors specific for epitopes on the organism's own molecules and so some of these B and T cells are destroyed by programmed cell death and the remaining self- reactive lymphocytes are typically rendered nonfunctional leaving only those lymphocytes that react to foreign molecules.

Prior exposure to an antigen alters the duration of

Speed strength and duration of the immune response

A benefit of fever is

Speeds. Up chemical reactions thus phagocytosis is stimulated and tissue repair is faster

Describe the structure of of host cells advertising that it has a foreign substance

The host proteins that displays the antigen fragment is called the major histocompability molecule. When a host cell takes in a pathogen enzymes cleave the antigen into smaller peptides and each peptide (antigen fragment) binds to an MHC molecule. Then the MHC and antigen fragment then move towards the surface of the cell and result in antigen presentation.

explain the two ways interferons work

The interferons that are secreted by virus-infected body cells induce nearby uninfected cells to produce substances that inhibit viral reproduction. On the other hand the interferons that are secreted by white blood cells help activate macrophages thus inducing their phagocytic ability.

How do the molecules that activate the vertebrate TRL signal transduction pathway differ from the Ligand in most other signalling pathways

The ligand for he TRL transduction partway is a foreign molecule and the ligand for many signal transduction pathways is a molecule produced by the molecule itself.

What is the same in each case of cellular innate defense?

The recognized macromolecule is normally absent from the vertebrate body and is an essential components of certain groups of pathogens

Sketch a B cell antigen receptor. Label the v and c regions of the light and heavy chains. Label the antigen binding sites, disulfide bridges and transmembrane region. Where are these features located relative to the v and c regions?

The transmembrane region lie within the c regions which also form the disulfide bridges. In contrast the antigen binding sites are in the v regions.

Immune cells of insects bind to molecules found only in the what of fungi and bacteria ? what serves as identification tags for each?

To the outer layers; fungal cell walls contain certain unique polysaccharides while bacterial cells walls have polymers containing of combinations of sugars and amino acid found in animal cells

Phagocytic cells that detect fungal or bacterial components use several times types of receptors, some mammalian receptors are very similar to what

Toll, a key activator in innate immunity in cells

T or F. Antigen presentation by a dendritic or macrophage activates a helper T cell which then proliferates forming a clone of activated cells.

True

What types of animals have both adaptive and innate immunity

Vertebrates

What is fever

a systemic inflammatory response

What are the peptides and proteins that pathogens or impede their reproduction?

antimicrobial peptides, interferons and complement proteins

Why does passive immunity only last as long as the antibodies last

because it does not involve the recipient's B and T cells

The death of an infected cell does what?

deprives the pathogen a place where to reproduce and exposes cell contents to circulating antibodies which mark released antigens for disposal

Where do antigen receptors of T cells bind to

fragments of antigens that are displayed on the surface of host cells

Antibodies can recognize

free antigens and the ones that are on the surface of pathogen's

B cell antigen receptors and antibodies bind to...

intact antigens in the blood and lymph

Describe the structure of a T cell receptor

it has two different polypeptide chains an alpha and a beta chain that are linked by a disulfide bridge. Near the base of a T cell antigen receptor is a transmembrane region that anchors the molecule in the cell's plasma membrane. Then at the outer tip of the molecule the variable regions in the alpha and beta regions form a single antigens binding site. The remainder of the molecule is made up of constant regions which is the display of the antigen fragment in an exposed groove of the MHC protein.

Define primary immune response

production of effector cells from a clone of lymphocytes during the first exposure to an antigen is the basis of the primary immune response. Overall this is the initial adaptive response to an antigen which appears to peak after about 10-17 after the initial exposure.

define interferons

proteins that provide innate defense by interfering with viral infections

What do cytotoxic T cells need to become activated?

signals from helper T cells an interaction with an antigen presenting cells.

How does fever come about

substances released by activated ,macrophages cause the body's thermostat to reset to a higher temperature

What are the four major characteristics of adaptive immunity

the first is that the diversity of lymphocytes and receptors enable the immune system to detect pathogens never before encountered. The second is adaptive immunity has self-tolerance. the third is cell proliferation triggered by activation increase the number of B and T cells available for a specific antigen. the fourth one is immunological memory which lets there be a more rapid response to previously encountered antigens. The first two arise as the lymphocyte matures and the last two after a mature lymphocyte encounters and binds to a specific antigen.

What cause the redness and increased skin temperature?

the increased blood flow

What happens after rearrange genes are transcribed, transcripts are processed for translations and translated?

the light and heavy chains assemble together forming an antigen receptor.

A systemic response means what

throughout the whole body