Chapter 10 Infection and Immunity
1 Pathogenicity of microorganisms
1.1 Host-parasite relationships
Infection: The invasion of a host by a microorganism with subsequent establishment and multiplication of the agent.
Infectious disease: Any change form a state of health in which part or all of the host’s body cannot carry on its normal functions because of the presence of an infectious agent or its products.
Pathogen: Any virus, bacteria or other agent that causes infectious disease. Its ability to cause disease is called pathogenicity.
1.2 Three main factors determinated the outcome of host-parasite relationships
(1) Pathogens
The virulence of the organism;
The number of organisms present in or on the host;
The entry point.
(3) Environmental conditions
1.3 Three outcomes of infection
2 Nonspecific immunity
Nonspecific immunity:
The natural immunity that offers resistance to any microorganisms or foreign material encountered by the vertebrate host.
3 Specific immunity
An immunity that develops after exposure to a suitable antigen or is produced after antibodies are transferred from one individual to another.
Four characteristics distinguish specific immunity from nonspecific resistance:
Specificity
Memory
Diversity
Discrimination between self and nonself
4 Immune system
5 Immune disorders
Hypersensitivities; Autoimmune diseases; Transplantation rejection;
Immunodeficiencies
6 Antigen-antibody interactions in vitro
ELISA (Enzyme-linked immunosorbent assay)
Flow cytometry and fluorescence
Neutralization
Radioimmunoassay
7 Vaccines and immunizations
Active immunization
Passive immunization
Immunity against microbe infection
I. Non-specific or innate immunity.
1. Anatomical barriers
(1) Skin and mucosa
Skin and mucous membranes
Acid pH
Fatty acids
Hydrolytic enzymes (lysozyme)
Proteolytic enzyems and bile
2. Phagocytic cells
Phagocytosis is a process describing the engulfment and destruction of extracellularly-derived materials by phagocytic cells, such as macrophages and neutrophils. Five steps of phagocytosis are illustrated in the image below.
(1) Schematic diagram of the steps in phagocytosis:
a. Attachment of the bacterium to the long membrane evaginations, called pseudopodia.
b. Ingestion of the bacterium forming a "phagosome," which moves toward the lysosome.
c. Fusion of the lysosome and phagosome, releasing lysosomal enzymes into the phagosome.
d. Digestion of the ingested material.
(2) Results of Phagocytosis
a. complete phaged
The lysosomes fuse with the phagosomes containing the ingested microbes and the microbes are destroyed
b. un-completed phaged
Some bacteria, such as Legionella pneumophilia (inf) and Mycobacterium species (inf), are more resistant to phagocytic destruction once engulfed.
3. NK cells
Role in early viral infection or tumorogenesis before activation of acquired immunity.
4. Secretory molecules
Complement system – 20 proteins in a controlled enzymatic cascade which targets the membrane of pathogenic organisms and targets theme for destruction
Interferons – proteins made by cells in response to virus infection that induced a generalized antiviral state in surrounding cells
II. Specific or adaptive immunity.
1. humora immunity
2. cell-mediated immunity
Section II Immunity against bacteria
I. anti- extracellular bacteria
1. Phagocytic cells: Neutrophils (PMN) and macrophages and monocytes are the most important cellular components of the non-specific immune system.
2. antibody and complement
3. cell mediated immune response
II. anti- extracellular bacteria
1. Phagocytic cells: Neutrophils (PMN) and macrophages and monocytes are the most important cellular components of the non-specific immune system.
2. cell mediated immune response
3. mucosa immunity: IgA is the major class of Ig in secretions - tears, saliva, colostrum, mucus. Since it is found in secretions secretory IgA is important in local (mucosal) immunity.
Section III Immunity against virus
I . Non-specific immunity:
A. Inherent Barriers Skin, Mucus, Ciliated epithelium , Low pH
B. NK cell
C. Humoral and cellular components
（1）. Interferon (IFN)
（2）. Complement
（3）. Cytokines TNF-a, IL-1 and IL-6
Interferon (IFN)
1. concept: a class of protein(glycoprotein) produced by cells in response to viral infection or other interferon inducers that protected other cells of same species from attack by a wide range of viruses.
2.classification of IFNs:
IFN-α | IFN-β | IFN-γ | |
Gene | chromosome 9 | chromosome 9 | chromosome 12 |
cell | blood mononuclear cell | fibroblasts | Ag-activated T cell |
anti-viral activity | +++ | +++ | ++ |
Modify-immune responses | ++ | ++ | +++ |
3. production of IFN:
(1) interferon inducers: eg. PolyI:C(poly inosinic:poly cytidylic acid), viruses and bacterial endotoxins, etc
(2) Mechanism :
IFN inducer acts on cell receptors --- IFN gene activation--- transcribe IFN mRNA--- IFN synthesis--- IFN released
4. antiviral activity:
not act directly on virus, but through induction of antiviral proteins(AVP).
(1) Mechanisms:
IFN combines with specific receptor on cell surface ---AVP gene actived --- AVP mRNA transcribed---AVP synthesis
AVP consists of : protein kinase 2,5-A synthetase
(2) Characteristics :
----not act directly on virus .
----broad-spectrum antiviral activity.
----host species specific: inhibit viral replication only in the species in which it was produced.
5. other activities:
(1) anti-cancer
(2) Modify immune responses
----NK activation
----macrophage activation
----Increased expression of MHC molecules
II. Specific immunity
1. Humoral immunity
1) Neutrilizing antibody: blocking the virus replication from binding and gaining entry to the host cell(by the inhibition of adsorption, penetration or uncoating).
(1)virolysis --- with the aid of complement----- by complement activation by antibody-coated virus particles.
--- by phagocytosis -----opsonins in enhancing phagocytosis of virus particles
--- by ADCC
(2)Neutrilizing virion: act on free viruses , but can’t influence intracellular virus directly.
2). Non-neutrilizing antibody:
hemagglutination inhibition antibodies
complement fixation antibodies:
2. Cell mediated immunity:
the destruction of an infected cell before progeny particles are released --- an effective way of terminating a viral infection.
CTL: react with membrane-bound viral antigens and lyse the infected cells.
release some lymphokines(IFN-r, TNF ).
Th : release lymphokines.
NK cell: lyse infected cell directly.
Section III Immunity against fungi
I . Non-specific immunity:
A. Inherent Barriers Skin, Mucus, Ciliated epithelium, Low pH
B. Phagocytic cells
C. Humoral and cellular components. --- IFN, TNF-a
II. Specific immunity
1. Humoral immunity----antibody
2. Cell mediated immunity:
Th : release lymphokines.
