microbiology lecture chapter 17

cellular cell mediated specific immunity

- based on action of T-cells (T-lymphocytes) that directly attack cells infected with viruses or parasites, transplanted cells or organs, and cancer cells. -(T-cells also regulate the activation and proliferation of macrophages)

ACTIVATION OF ANTIBODY -PRODUCING CELLS BY CLONAL SELECTION

-A B-cell becomes activated when an antigen reacts with antigen receptors on its surface -The activated B cell produces a clone of plasma cells and memory cells. -The plasma cells secrete antibodies. -Memory cells recognize pathogens from previous encounters. -T cells and B cells that react with self antigens are destroyed during fetal development; this is called clonal deletion.

antigen must be processed

-An antigen must be processed by an Antigen -Presenting Cell (APC) and positioned on the surface of the APC -The major histocompatibilty complex (MHC) consist of cell surface proteins unique to each individual -A T-Cell recognizes antigen in association with MHC on APC

clonal selection

-Bone marrow gives rise to B cells. -Mature B cells migrate to lymphoid organs. -A mature B cells recognizes epitopes.

cytokines

-Cells of the immune system communicate with each other by means of chemicals called cytokines. -may be useful in treating tumors

t cells t lymphocytes

-Develop from stem cells in the bone marrow -Mature in the Thymus gland -After maturation in thymus, they migrate to lymphoid tissue -Differentiate into effector T cells when they are stimulated by an antigen -Some effector T cells become memory cells a. Not transferred to fetus via the placenta -Each T-cell reacts specifically with only one type of antigen. -Specialized cells that respond to intracellular Ags -Body's ability to make new T-cell decreases with age, beginning with late adolescence -Cell mediated immunity primarily involves T-cells that respond to intracellular antigens -Do not secrete antibodies. -Some attack host cells that have become infected with viruses, fungi, transplanted human cells, and cancerous cells. -Must come in close or direct contact to destroy the target cells.

t independent antigens

-Do not require assistance of helper T-cells -Mainly polysaccharides or lipopolysaccharides (capsules etc.) -They have repeating unit that cross-link several receptors on same B cell. B cell then produce antibodies

immunity

-From Latin word "immunis" meaning to exempt -Immunity is the ability of the body to specifically counteract foreign organisms or substances called antigens. -Immunity results from the production of the specialized lymphocytes and antibodies. -Specific antibody and lymphocyte response to an antigen is called specific immmunity

lymphocytes and lymphoid organs

-Lymphocytes are derived from stem cells in the bone marrow. -Stem cells produce the specialized blood cells. -Stem cells replace themselves by cell division so the stem cell population is not depleted. -Lymphocytes produced by this process seed the thymus, spleen, and lymph nodes. -Lymphocytes produce self-replacing lymphoid colonies in these organs. -Since bone marrow and the thymus produce the T and B lymphocytes, they are called Primary lymphoid organs -Both T and B cells function in specific immunity.

IgE antibodies

-Monomer -0.002% (rarest) of serum antibodies -On mast cells and basophils, in blood -Participate in allergic reactions -Lysis of parasitic worms -Attract IgG, Complement, and phagocytic cells -Half-life = 2 days

IgD antibodies

-Monomer -0.2% of serum antibodies -In blood, lymph, on B cells -On B cells, act as antigen receptor, initiate immune response -Half-life = 3 days

IgG antibodies

-Monomer -Smallest of the five -80% of serum antibodies -In blood, lymph, intestine -Cross walls of blood vessels, enter tissue fluid -Only type that can cross placenta -Enhance phagocytosis; neutralize toxins & viruses; protects fetus & newborn -Activate the complement system -Half-life = 23 days

IgM antibodies

-Pentamer -Largest of the five -5-10% of serum antibodies -Activate complement system -In blood, lymph, on B cells -Agglutinates microbes -First Antibodies (Ab) produced in response to infection -The primary antibody against A and B antigens on red blood cells -Half-life = 5 days

antibodies

-Protein (Immunoglobulins) made in response to an antigen and can recognize and bind that antigen -help destroy or neutralize the specific antigen -found in the serum

t dependent

-Require assistance of Helper T-cells -When Th bind with MHC-antigen complex produces IL-2 that influence B cells to produce antibodies. Th also activate B cell directly - Mainly proteins (on viruses, bacteria, foreign RBC etc

third line of defense

-The human specific immune system recognizes foreign substances as not belonging to the body and develops a specific immune response against them (Immunity) -The characteristic of specificity and memory distinguish the specific immune response from non- specific resistance -Substances that provoke a specific response are called antigens -The immune response involves the production of proteins called antibodies and certain specialized lymphocytes. -The immune system comprises * Cells * Proteins * Lymphatic system

immunologicial memory

-The response of the body to the first contact with an antigen is called the primary response. It is characterized by the appearance IgM followed by IgG. -Subsequent contact with the same antigen results in a very high antibody titer and is called the secondary, anamnestic, or memory response. The antibodies produced this time are primarily IgG.

passive immunity is short lived

-When antibodies (immune serum globulins) from a person who has immunity against a disease are injected to another person, it gives the recipient immediate protection against that particular disease. This immunity is short lived because half life of antibodies is very short and the body keeps no memory of such treatment -Antibodies of mother are transferred to her baby through placenta or by milk and provide the baby a short term protection against infections experienced by the mother

acquired immunity

-developed during an individuals lifetime

immunoglobulin structure

1. antigen binding site 2. antigen 3. antigenic determinant

antibody formation: clonal selection theory

1. b cells encounter and bind to antigen 2. b cell c response to antigen by proliferating clone of b cells 3. some b cells differentiate into long lived memory cells 4. other be cells differentiate into plasma cells 5. plasma cells secrete antibodies into circulation

specific defenses cells response to agntigens

1. stem cell 2. thymus 3. t cell 4. lymphnode 1. stem cell 2. cut associated lymphoid tissue, such as liver or bone marros 3. b cell 4. lymphnode

Antigens (Antibody generators)

Also called as immunogens Provoke a highly specific immune response in an organism Most antigens are proteins or large polysaccharides - Lipids and nucleic acids are antigenic when combined with proteins or polysaccharides Antigenic compounds are 1. Microbial components 2. Non-microbial

antibodies structure

An antibody has at least two identical antigen-binding (valance) sites A single bivalent antibody unit is a monomer. Typical monomers consist of four polypeptide chains. Within each chain is a variable (V) region, where antigen binding occurs, and a constant (C) region, which serves as a basis for distinguishing the classes of antibodies. An antibody monomer is Y- or T-shaped; the variable regions form the tips, and the constant regions form the base and Fc (stem) region. The Fc region can attach to a host cell or complement.

Antigenic determinants or epitopes

Antigenic determinants or epitopes are specific regions present on an antigen that are recognized by antibodies

self tolerance

Body doesn't make Antibodies against self antigen Clonal deletion -The process of destroying B and T cells that react to self antigens

microbial components

Capsules, cell wall, flagella, fimbriae, toxins of bacteria, coats of viruses, other types of microbial surfaces

cytotoxic t cells

Cytotoxic T-Cells (Tc) or CD8 destroy target cells by two way a) initiation of apoptosis b) release of porins that damage the target cell membrane, resulting in cytolysis of target cells

Cytotoxic T-Lymphocytes

Cytotoxic T-Lymphocytes (CTL) A Tc can differentiate into an effector cell called CTL. CTL attach by their T-cells receptor to virus infected cells that display class 1 MHC proteins and viral antigens; are then stimulated by T-Helper cells; activated cytotoxic cells produce cytokines that limit viral reproduction and activate macrophages

delayed hypersensitivity t

Delayed Hypersensitivity T (TD) associated with certain types of allergic reactions

helper t cells

Helper T-cells (TH) or CD4 secrete cytokines (IL-2) that activate other T-cells and B-cells. * TH bind to MHC class II molecules on B cell and APCs

humor specific immunity

Humoral (antibody-mediated) immunity - based on action of antibody that bind bacteria, toxins, and extracellular viruses, tagging or marking them for destruction. B-cells (B-lymphocytes) are responsible for the production of antibodies

apoptosis

Lymphocytes that are not needed undergo apoptosis, or programmed cell death, and are destroyed by phagocytes.

b lymphoctes (b cells)

Provide humoral immunity: Most of the lymphocytes that are not T cells are B lymphocytes (B cells). Processed in the bone marrow. Function in specific immunity. B cells combat bacterial and some viral infections. - Secrete antibodies into the blood and lymph. - Provide humoral immunity as blood and lymph are body fluids (humors). Stimulate production of memory cells: - Important in active immunity. Others are transformed into plasma cells: Plasma cells produce ~2000 antibody proteins/second when exposed to an antigen. - These antigens may be isolated molecules or may be molecules at the surface of an invading foreign cell. - Serves to identify the enemy. Secrete antibodies that bind to antigens.

functions of specific immune response

Specific immune response has three major function 1. Recognize anything that is non-self 2. Respond to this foreign material - involves the recruitment of various defense molecules and cells to either destroy foreign material or render it harmless 3. Remember the foreign invader - a more rapid and intense responses to foreign material that occurs upon later encounters with the material

T regulatory cells

T regulatory cells (Treg) formerly called Suppressor T (TS) cells appear to regulate the immune response (combat autoimmunity by suppressing T cells that escape deletion in thymus * 5 -10% of T cell population * They are subset of T helper cells with additional CD25 molecules

types of t cells

T-Cells are classified according to their functions and cell surface receptors called CD (Clusters of Differentiation). T - cell are of following types 1. cytotoxic 2. helper t cells 3. delated hypersensitivity t 4. t regulatory cells

IgA antibodies

Two types 1. Dimer (secretory) 2. Monomer (non - secretory) in serum (less effective) -10-15% of serum antibodies -Present in mothers milk -In secretions -Mucosal protection -Half-life = 6 days

antibody dependent cell mediated toxicity

With the help of the antibodies produced by the humoral immune system, the cell mediated immune system can stimulate NK cell and cells of the nonspecific defense system to kill target organism like protozoan or helminthes

antigen (Ag)

a substances that is foreign to the body causes the body to trigger an immune response (produce specific antibodies or sensitized T cells)

microbes are mosaic

antibodies recognize and react with antigenic determinants or epitopes

interferons

are cytokines that protect against viruses

interleukins (IL)

are cytokines that serve as communicators between leukocytes

chemokines

cause leukocytes to move to the site of infection

innate (non specific)

defenses against any pathogen; has an inherited genetic component

active

exposure to antigen -natural: via infection -artificial: via vaccines (solution containing antigen (long lived)

antiserum

generic term for serum because it contains Ab

adaptive immunity (specific)

is induced; body adapts to a microbial invader or a foreign substances

non microbial components

pollens, egg white, blood cell surface molecules, serum proteins from others, surface molecules of transplanted tissue or organs

antibody (Ab)

proteins made in response to an antigen

gamma globulin

serum fraction containing Ab

globulins

serum proteins

serology

study of reactions between antibodies and antigen

Interrelationship of cell mediated and humoral immunity

the production of antibodies by 1. t dependent antigens 2. t independent antigens

passive

transfer of antibodies -natural: transplacental (across placenta); colostrum (early milk produced by mother) is full of antibodies to develop immunity artificial: introduction of antibodies from an immune donor into an individual (short lived)