Bio 102 Exam 2 (Ch. 43, 44, 46, 47)

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Innate immunity

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(All animals)

The recognition of traits shared by broad ranges of pathogens, using a set of receptors. Includes barrier defenses like skin, mucous membranes, and secretions, and internal defense like phagocytic cells, natural killer cells, antimicrobial proteins, and inflammatory response

Is faster than adaptive immunity

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Adaptive immunity

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(Vertebrates only)
The recognition of traits specific to particular pathogens, using a vast array of receptors. Slower response that innate immunity.

Humoral response: antibodies defend against infection in body fluids

Cell-mediated response: Cytotoxic cells defend against infection in body cells

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Specificity

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A characteristic of acquired immunity. It refers to how lymphocytes respond to invaders through the recognition of particular molecules. "Lock and key"

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Diversity

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A characteristic of acquired immunity. It refers to the remarkable diversity in lymphocytes and receptors that enable the immune system to detect pathogens that were never before encountered. See slide on Immunoglobin Genetic Recombination

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Lymphocyte

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A type of white blood cell. The adaptive immune response of vertebrates relies on T cells and B cells, two types of lymphocytes.

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T cells

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Lymphocytes that develop in the thymus, an organ in the thoracic cavity above the heart, after originating from the bone marrow

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B cells

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Lymphocytes that remain and mature in the bone marrow. When stimulated by an antigen and the cytokines secreted from helper T cells, B cells proliferate and differentiate into memory B cells and antibody secreting effector cells called plasma cells.

B cells make antibodies (immunoglobins) which tag pathogens for destruction.

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Antigen

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Any substance that elicits a response from a B cell or T cell

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Antigen receptor

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In adaptive immunity, recognition occurs when a B cell or T cell binds to an antigen, such as a bacterial or viral protein, via a protein called an antigen receptor. An antigen receptor is specific enough to bind to just one part of one molecule from a particular pathogen, such as a species of bacteria or strain of virus.

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Epitope

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The small, accessible portion of an antigen that binds to an antigen receptor. Is also called an antigenic determinant. A single antigen usually has several different epitopes, each binding a receptor with a different specificity.

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Antibody/immunoglobin (Ig)

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An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shape protein produced by plasma cells (like B cells) that is used by the immune system to identify and neutralize pathogens such as bacteria and viruses. Each antibody binds to a specific antigen.

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Neutrophil

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INNATE IMMUNITY - A main phagocytic cell

A phagocytic cell which circulates in the blood and are attracted by signals from infected tissues. They then engulf and destroy the infecting pathogens.

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Macrophages

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INNATE IMMUNITY - A main phagocytic cell

"Big eaters". They are larger phagocytic cells. Some migrate throughout the body while others reside permanently in organs and tissues where they are likely to encounter pathogens.

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Phagocytosis

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The cellular ingestion and digestion of bacteria and other foreign substances. It works by a phagocytic cell engulfing a pathogen, forming a vacuole around it, fusing the vacuole and the lysosome, toxic compounds and lysosomal enzymes destroying the pathogen, and finally the release of debris from pathogens by exocytosis.

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Inflammatory response

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The changes brought about by signaling molecules released upon injury or infection.

1. Chemical signaling: Starts inflammation process. At the injury site, mast cells release histamines and macrophages secrete cytokines. These signaling molecules cause nearby capillaries to dilate.

2. Vasodilation: Because of histamine, capillaries widen and become more permeable, allowing fluid containing antimicrobial peptides to enter the tissue. Signals released by immune cells attract neutrophils.

3. Phagocytosis: neutrophils digest pathogens and cell debris at the site, and tissue heals

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pyrogen

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During innate immune responses, chemicals trigger the release of more neutrophils from the bone marrow.

Toxins (pyrogens) released from leukocytes to increase the set temperature (homeostasis).

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Interferons

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Proteins that provide innate defense by interfering with viral infections. Virus-infected body cells secrete interferons, which induce nearby uninfected cells to produce substances that inhibit viral reproduction

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Complement system

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The infection fighting complement system consists of roughly 30 proteins in blood plasma. These proteins circulate in an inactive state and are activated by substances on the surface of many microbes. Activation results in a cascade of biochemical reactions that can lead to lysis (bursting) of invading cells.

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Clonal selection

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When an antigen receptor binds to an epitope, the lymphocyte is activated. Once activated, the B or T cells undergoes multiple cell divisions. For each activated cell the result of their proliferation is a clone, a population of cells that are identical to the original cells. Some cells from this clone become effector cells, while others become memory cells. This process is called clonal selection.

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Immunologic memory

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The capacity to generate a secondary immune response is due to memory cells that arise from the initial exposure to an antigen.

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Self-tolerance

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When lymphocytes mature, their antigen receptors are tested for self-reactivity. If they bind to themselves, they are destroyed by APOPTOSIS, programmed cell death.

This process leaves only B and T cells which react to foreign molecules.

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MHC proteins or MHC Complex

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It is a "biochemical fingerprint".

An MHC (major histocompatibility complex) protein is the host protein (the host cell having been infected by a pathogen) that displays the antigen fragment on its cell surface, which T cells bind to.

Two classes: class I is found on nearly every nucleated body. Class II are restricted to specialized cell types like macrophages, activated T-cells, B cells, and cells in the interior of the thymus.

MHCs determine which T cells will survive or not during their maturation in the thymus.

For each MHC gene there are multiple alleles, and

MHC proteins are one of most polymorphic protein families.

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Cytotoxic T cell

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TC - have receptors that bind to MHC Class I molecules. The are responsible for a cell-mediated response, in which specialized effector cytotoxic T cells destroy infected host cells. They are the "killer" T cells, killing by inducing apoptosis.

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Helper T cell

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TH - have receptors that bind MHC Class II molecules. Their role is to send out signals that cause other cells to attack pathogens. This is central to B and T cell responses.

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Primary Immune Response

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The first time a body is exposed to a particular antigen, selective proliferation and differentiation of lymphoctyes occurs.

The primary response peaks 10-17 days after exposure. During this time, selected B cells and T cells give rise to their effector forms.

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Secondary Immune Response

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The second time a body is exposed to a particular antigen, the response is much faster (2-7 days). The response is now longer and stronger.

The secondary immune response is a hallmark of adaptive (or acquired) immunity.

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Effector cells

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Cells which arise from clonal selection that take effect immediately against the antigen and any pathogens producing that antigen.

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Memory cells

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The cells that arose from clonal selection that did not take effect immediately. They instead became memory cells, long-lived cells that can give rise to effector cells if the same antigen is encountered later in the animal's life.

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Genetic Variation of Immunoglobin genes

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By combining variable elements, the immune system assembles many different receptors from a much smaller collection of parts.

1. DNA from an undifferentiated B cell is deleted between randomly selected V and J segments of a strand, creating a differentiated B cell.

2. The permanently rearranged, functional gene of the DNA of the differentiated B cell is transcribed into pre-mRNA.

3. RNA processing occurs

4. mRNA translation occurs, resulting in a light chain that combines with a polypeptide produced from an independently rearranged heavy-chain gene to form a functional receptor.

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Ig G

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Abundant in blood circulation. They are the most abundant of circulating antibodies. It readily crosses the walls of blood vessels and enters tissue fluids. It protects against bacteria, viruses, and toxins in the blood and lymph, and triggers action of the complement system.

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Ig M

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The first circulating antibodies to appear in response to an initial exposure to an antigen; their concentration in the blood then declines rapidly. Thus the presence of IgM usually indicates a current infection. Very large (pentamer) composes of five Y-shaped monomers.

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Ig A

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It is produced by cells in mucous membranes. The main function of IgA is to prevent the attachment of viruses and bacteria to epithelial surfaces. IgA is also found in many body secretions, such as saliva, perspiration, and tears. Its presence in the first milk produced helps protect the infant from gastrointestinal infections

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Ig D

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IgD antibodies do not activated the complement system and cannot cross the placenta. They are mostly found on the surfaces of B cells, probably functioning as antigen receptors that help initiate the differentiation of B cells into plasma cells and memory B cells.

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Ig E

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IgE molecules are slightly larger than IgG and represent only a small fraction of the antibodies in the blood. The tails attach to mast cells and basophils and, when triggered by an antigen, cause the cells to release histamine and other chemicals that cause an allergic reaction.

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allergies

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Exaggerated (hypersensitive) responses to certain antigens called allergens. The most common allergies involve antibodies of the IgE class (see: IgE slide)

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anaphylactic shock

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A whole-body, life threatening reaction that can occur within seconds of exposure to an allergen. It develops when widespread release of mast cell contents triggers abrupt dilation of peripheral blood vessels, causing a precipitous drop in blood pressure and constriction of the bronchioles. Death may occur in minutes to lack of blood flow and the inability to breather. The hormone epinephrine counteracts this allergic response.

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Autoimmune Diseases

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When the immune system is active against particular molecules of the body. Examples include lupus, rheumatoid arthritis, and multiple sclerosis.

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***Compare the innate and adaptive immunity of animals.

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Innate immunity is found in all animals (as well as in plants). Invertebrates like insects have an exoskeleton, chitin based barriers, and immune cells like hemocytes that travel throughout insect lymph and perform phagocytosis.They do not have adaptive immunity because this requires the lymphocytes of white blood cells.

Vertebrates have both innate and acquired immunity. Mammals have epithelial tissues that black the entrance of pathogens, inflammatory responses, mucus ( a viscous fluid that traps microbes) and phagocytic cells like neutrophils and macrophages. Adaptive immunity is unique to vertebrates.

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***Describe the inflammatory response.

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1. At the injury site, mast cells release histamines and macrophages secrete cytokines. These signalling molecules cause nearby capillaries to dilate.

2. Vasodilation: capillaries widen and become more permeable, allowing fluid containing antimicrobial peptides (short chains of amino acids that circulate throughout the body and inactive or kill fungi and bacteria by disrupting their plasma membranes) to enter the tissue. Signals released by immune cells attract neutrophils.

3. Phagocytosis: Neutrophils digest pathogens and cell debris at the site. Tissue heals.

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***Describe phagocytosis.

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1. Pseudopodia (the temporary projections or "feet" of the eukaryotic cells) surrounds pathogens.

2. Pathogens are engulfed by endocytosis

3. Vacuole forms, enclosing pathogens.

4. Vacuole and lysosomes containing enzymes fuse

5. Toxic compounds and lysomal enzymes destroy pathogens.

6. Debris from pathogens is released by exocytosis

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***Which 2 types of white blood cells are capable of phagocytosis?

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Neutrophils, which circulate in the blood and are attracted by infected tissues, and macrophages, which both migrate throughout the body and reside permanently in organs and tissues where they are likely to encounter pathogens.

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*** Identify the cells ofAcquired Immunity.

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Acquired immunity depends on T cells and B cells, which are types of white blood cells called lymphocytes.

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***Name the types of cells involved inHumoral Immunity

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In the humoral immune response, antibodies help neutralize or eliminate toxins in the blood or lymph. It requires:

1. an antigen-presenting cell to engulf and degrade a pathogen

2. a specific helper T cell to identify the class II MHC molecule and antigen fragment being presented, to attach itself to the antigen-presenting cell, and to release cytokines

3. a B cell with receptors for the same epitope to be stimulated by the cytokines released by the helper T cell. It will create plasma cells and memory B cells

4. plasma cells to secrete antibodies that are specific to the antigen that initiated the response. The antibodies bind to antigens, marking the pathogen for inactivation or destruction

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***Name the types of cells involved in Cell Mediated Immunity