Dr. Taj
IMMUNITY
The Immune ResponseThe Immune Response
Immunity: “Free from burden”. Ability of anorganism to recognize and defend itselfagainst specific pathogens or antigens.Immunity: “Free from burden”. Ability of anorganism to recognize and defend itselfagainst specific pathogens or antigens.
Immune Response: Third line of defense.Involves production of antibodies andgeneration of specialized lymphocytesagainst specific antigens.Immune Response: Third line of defense.Involves production of antibodies andgeneration of specialized lymphocytesagainst specific antigens.
Antigen: Molecules from a pathogen orforeign organism that provoke a specificimmune response. Usually have a molecularwt. of more than 8000 D.Antigen: Molecules from a pathogen orforeign organism that provoke a specificimmune response. Usually have a molecularwt. of more than 8000 D.
The Immune System is the ThirdLine of Defense Against Infection
Immunity -- Types
1.Innate immunity
Non-specific: Examples:
•Ingestion of invading organisms (phagocytosis)
•Stomach acidity
•Skin barrier
•Lysozyme
•Natural killer lymphocytes
2. Acquired immunity:
the result of attack by bacteria, viruses etc
–e.g. Vaccination
–Long lasting (Memory)
Immunity -- Types
Acquired immunity:
•Specific against individual bacteria, virus,toxin, foreign tissues
•Basic types of acquired immunity:
Humoral immunity
(B-cell immunity)
B-LYMPHOCYTES
Antibodies
Cell-mediated immunity
(T-cell immunity)
Activated T-LYMPHOCYTES
Initiated by antigens
AntigensAntigens
uMost are proteins or large polysaccharides froma foreign organism.uMost are proteins or large polysaccharides froma foreign organism.
uMicrobes: Capsules, cell walls, toxins, viral capsids,flagella, etc.uMicrobes: Capsules, cell walls, toxins, viral capsids,flagella, etc.
uNonmicrobes: Pollen, egg white , red blood cellsurface molecules, serum proteins, and surfacemolecules from transplanted tissue.uNonmicrobes: Pollen, egg white , red blood cellsurface molecules, serum proteins, and surfacemolecules from transplanted tissue.
uLipids and nucleic acids are only antigenic whencombined with proteins or polysaccharides.uLipids and nucleic acids are only antigenic whencombined with proteins or polysaccharides.
uMolecular weight of 8,000 or higher.uMolecular weight of 8,000 or higher.
uHapten: Small foreign molecule that is not antigenic. Must becoupled to a carrier molecule to be antigenic. Once antibodiesare formed they will recognize hapten.uHapten: Small foreign molecule that is not antigenic. Must becoupled to a carrier molecule to be antigenic. Once antibodiesare formed they will recognize hapten.
AntibodiesAntibodies
uProteins that recognize and bind to a particularantigen with very high specificity.uProteins that recognize and bind to a particularantigen with very high specificity.
uMade in response to exposure to the antigen.uMade in response to exposure to the antigen.
uOne virus or microbe may have several antigenicdeterminant sites, to which different antibodiesmay bind.uOne virus or microbe may have several antigenicdeterminant sites, to which different antibodiesmay bind.
uEach antibody has at least two identical sitesthat bind antigen: Antigen binding sites.uEach antibody has at least two identical sitesthat bind antigen: Antigen binding sites.
uValence of an antibody: Number of antigenbinding sites. Most are bivalent.uValence of an antibody: Number of antigenbinding sites. Most are bivalent.
uBelong to a group of serum proteins calledimmunoglobulins (Igs).uBelong to a group of serum proteins calledimmunoglobulins (Igs).
Types of Acquired ImmunityTypes of Acquired Immunity
I. Naturally Acquired Immunity: Obtained inthe course of daily life.I. Naturally Acquired Immunity: Obtained inthe course of daily life.
A. Naturally Acquired ACTIVE Immunity:A. Naturally Acquired ACTIVE Immunity:
u Antigens or pathogens enter body naturally.u Antigens or pathogens enter body naturally.
uBody generates an immune response to antigens.uBody generates an immune response to antigens.
uImmunity may be lifelong (chickenpox or mumps)or temporary (influenza or intestinal infections).uImmunity may be lifelong (chickenpox or mumps)or temporary (influenza or intestinal infections).
B. Naturally Acquired PASSIVE Immunity:B. Naturally Acquired PASSIVE Immunity:
uAntibodies pass from mother to fetus via placentaor breast feeding (colostrum).uAntibodies pass from mother to fetus via placentaor breast feeding (colostrum).
uNo immune response to antigens.uNo immune response to antigens.
uImmunity is usually short-lived (weeks to months).uImmunity is usually short-lived (weeks to months).
uProtection until child’s immune system develops.uProtection until child’s immune system develops.
Types of Acquired Immunity (Continued)Types of Acquired Immunity (Continued)
II. Artificially Acquired Immunity: Obtained byreceiving a vaccine or immune serum.II. Artificially Acquired Immunity: Obtained byreceiving a vaccine or immune serum.
1. Artificially Acquired ACTIVE Immunity:1. Artificially Acquired ACTIVE Immunity:
uAntigens are introduced in vaccines(immunization).uAntigens are introduced in vaccines(immunization).
uBody generates an immune response to antigens.uBody generates an immune response to antigens.
uImmunity can be lifelong (oral polio vaccine) ortemporary (tetanus toxoid).uImmunity can be lifelong (oral polio vaccine) ortemporary (tetanus toxoid).
2. Artificially Acquired PASSIVE Immunity:2. Artificially Acquired PASSIVE Immunity:
u Preformed antibodies (antiserum) are introducedinto body by injection.u Preformed antibodies (antiserum) are introducedinto body by injection.
FSnake antivenom injection from horses orrabbits.FSnake antivenom injection from horses orrabbits.
uImmunity is short lived (half life three weeks).uImmunity is short lived (half life three weeks).
uHost immune system does not respond to antigens.uHost immune system does not respond to antigens.
The bases ofAcquired Immunityare Lymphocytes
Immune cells
Two types:
1.B-Lymphocytes
(Thymus independent, B-lymphocytes)
Produce antibodies
(Humoral Immunity)
2.T- lymphocytes
(Thymus dependent, T-lymphocytes)
Cellular mechanisms
(Cellular Immunity)
Lymphocytes
B-lymphocytes
T-lymphocytes
Develop in the lymphnodes and spleen.
Life span: 2-7 days (shortlived lymphocyte).
Principal mediators ofhumoral immune responses.
These produce antibodiesthat are capable of attackingthe invading agent.
This type of immunity iscalled “humoral immunity”.
Originate in the thymus orbone marrow.
Life span: 100-300 days (longlived lymphocytes).
Principal mediators ofcellular immune responses.
They are specificallydesigned to destroy theforeign agent.
This type of immunity iscalled “cell-mediatedimmunity”.
Lymphocytes cont….
B-Lymphocytes
•B lymphocytes transform into plasma cellsand secrete antibodies
(17.6b)
T-Lymphocytes
•T lymphocytes can attack foreign cellsdirectly
(17.6)
T Cells Only Recognize AntigenAssociated with MHC Molecules onCell Surfaces
Humoral Response to T DependentAntigens
Humoral Response to T DependentAntigens
T-Lymphocytes(thymus dependent)
Types of T-lymphocytes
–T-helper
–T-cytotoxic
–Natural killer
Functions
–Cellular immunity
•graft rejection
•delayed hypersensitivity.
–Help in antibody secretion.
Central Role of Helper T Cells
Cytotoxic T cells
Cytotoxic T Cells Lyse Infected Cells
Duality of Immune SystemDuality of Immune System
I. Humoral (Antibody-Mediated) ImmunityI. Humoral (Antibody-Mediated) Immunity
uAntibodies are produced by a subset of lymphocytescalled B cells.uAntibodies are produced by a subset of lymphocytescalled B cells.
uInvolves production of antibodies against foreignantigens.uInvolves production of antibodies against foreignantigens.
uB cells that are stimulated will actively secreteantibodies and are called plasma cells.uB cells that are stimulated will actively secreteantibodies and are called plasma cells.
uAntibodies are found in extracellular fluids (bloodplasma, lymph, mucus, etc.) and the surface of B cells.uAntibodies are found in extracellular fluids (bloodplasma, lymph, mucus, etc.) and the surface of B cells.
uDefense against bacteria, bacterial toxins, and virusesthat circulate freely in body fluids, before they entercells.uDefense against bacteria, bacterial toxins, and virusesthat circulate freely in body fluids, before they entercells.
uAlso cause certain reactions against transplantedtissue.uAlso cause certain reactions against transplantedtissue.
Antibodies are Produced by B Lymphocytes
Antibodies are Proteins that Recognize Specific Antigens
Duality of Immune System (Continued)Duality of Immune System (Continued)
II. Cell Mediated ImmunityII. Cell Mediated Immunity
uInvolves specialized set of lymphocytes called T cells thatrecognize foreign antigens on the surface of cells,organisms, or tissues:uInvolves specialized set of lymphocytes called T cells thatrecognize foreign antigens on the surface of cells,organisms, or tissues:
FHelper T cellsFHelper T cells
FCytotoxic T cellsFCytotoxic T cells
uT cells regulate proliferation and activity of other cells ofthe immune system: B cells, macrophages, Neutrophils,etc.uT cells regulate proliferation and activity of other cells ofthe immune system: B cells, macrophages, Neutrophils,etc.
uDefense against:uDefense against:
FBacteria and viruses that are inside host cells and are inaccessibleto antibodies.FBacteria and viruses that are inside host cells and are inaccessibleto antibodies.
FFungi, protozoa, and helminthsFFungi, protozoa, and helminths
FCancer cellsFCancer cells
FTransplanted tissueFTransplanted tissue
Cell Mediated Immunity is Carried Out by T Lymphocytes
Immunological MemoryImmunological Memory
Pattern of Antibody Levels During InfectionPattern of Antibody Levels During Infection
Primary Response:Primary Response:
uAfter initial exposure to antigen, no antibodies arefound in serum for several days.uAfter initial exposure to antigen, no antibodies arefound in serum for several days.
uA gradual increase in titer, first of IgM and thenof IgG is observed.uA gradual increase in titer, first of IgM and thenof IgG is observed.
uMost B cells become plasma cells, but some B cellsbecome long living memory cells.uMost B cells become plasma cells, but some B cellsbecome long living memory cells.
uGradual decline of antibodies follows.uGradual decline of antibodies follows.
Immunological Memory (Continued)Immunological Memory (Continued)
Secondary Response:Secondary Response:
uSubsequent exposure to the same antigen displaysa faster and more intense antibody response.uSubsequent exposure to the same antigen displaysa faster and more intense antibody response.
uIncreased antibody response is due to theexistence of memory cells, which rapidly produceplasma cells upon antigen stimulation.uIncreased antibody response is due to theexistence of memory cells, which rapidly produceplasma cells upon antigen stimulation.
Antibody Response After Exposure to Antigen
