Diagnostic immunology
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DIAGNOSTIC IMMUNOLOGY. IMMUNITY TO INFECTION. Major classes of pathogens. Definitions Two organisms live in close association. Mutualism: Both members benefit from the association. e.g., Protozoa live in the gut of termites .

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Diagnostic immunology
DIAGNOSTIC IMMUNOLOGY

IMMUNITY TO INFECTION



Definitions

Two organisms live in close association.

Mutualism:Both members benefit from the association.

e.g., Protozoa live in the gut of termites.

Communalism:When an organism benefits from the host but the host neither benefits nor is harmed.

e.g. Entomoeba gingivalis in human mouth.

*Parasitism:When an organism actually harms its host or lives at the expense of the host.

e.g., Infections with viruses, bacteria, fungi, protozoa, or helminthes.


If no innate immunity

The course of a typical infection and immune responses can be divided into phases



Types of defense systems
TYPES OF DEFENSE SYSTEMS factors:

1- Immediate immune response

  • Complement

  • Phagocytosis

  • Natural Antibodies

    2- Early immune response

    3- Late immune response


The early ir
The Early IR factors:

  • 4-96 hours past infection

    1- Macrophages >>>> Cytokines

    Increase vascular permeability

    Recruits polymorphs and macrophages

    Triggers platelets activation

    2- Natural killer cells ( Viral infection)

    3- Interferon's


The late ir
The Late IR factors:

  • After about 4 days

  • Degradation and Ag presentation

  • MHC molecules involvement

  • Activation of T and B lymphocytes

  • Cellular and humoral response

  • Specific antibodies


Immunity to bacterial infection
Immunity to Bacterial Infection factors:

  • The first line of defense is NOT dependent on antigen recognition

    • Innate immunity

    • Complement activation

    • Phagocytosis

    • NK cells


Most bacteria are killed by phagocytosis: factors:

  • Oxygen independent killing

  • Cationic proteins killing

  • Acidic pH and lactoferrin

    Complement is an effective mechanism but bacteria may be able to avoid complement mediated damage.


The second line of defense is characterized by the secretion of specific antibodies;

  • Neutralize toxins by preventing its binding to the target

  • Interfere with motility by binding to flagellae

  • SecretoryIgA stops binding to epithelial cells

  • Aid in targeting complement


Immunity to fungal infection
Immunity To Fungal Infection of specific antibodies;

  • Is a growing problem in immunologically compromised hosts

  • Seen in HIV infection

  • Seen in cancer patients undergoing chemotherapy

  • Patients on immunosuppressive drugs

  • In patients taking long term corticosteroids



Proposed mechanisms
Proposed mechanisms of specific antibodies;

Based on cell immunity:

T Helper cells

Cytokines

Activation of macrophages

Elimination of fungi


Immunity to viruses
Immunity to Viruses of specific antibodies;

  • Viruses are obligate intracellular microorganisms

  • They require the host cells to drive protein synthesis and metabolize sugar

  • Viroids are infectious agents that consist of nucleic acids alone

  • Prions are infectious proteins associated with degenerative neurological diseases of human


Innate ir to viral infection
Innate IR to viral infection of specific antibodies;

  • The early stage of the infection is a race between the virus and the host IS

  • The initial defense is the integrity of the body surfaces

  • Innate defense system involves;

    Interferon

    Nk cells

    Macrophages


Mechanisms involving t cells
Mechanisms involving T cells of specific antibodies;

CD8+ cells ;These are MHC class 1 restricted cells that focus on the site of virus replication and destroy virus infected cells

CD4+ cells ;

Key factor in defense against viral infection

INF gamma is important for the activation of TNF alpha which induce apoptosis


Evading ir by viruses
Evading IR by Viruses of specific antibodies;

  • Mutation

  • Producing of short stretches of RNA that work against interferon

  • Production of proteins that inhibit transporting to cell surface such as in infection with CMV


Immunopathology of viral infection
Immunopathology of Viral Infection of specific antibodies;

1- Response to viral infection may cause tissue damage

Ag-Ab complex deposition in kidney and blood >>> inflammatory response >>> T cell mediated damage >> killing of host cells

2- Virus may infect immune cells

3- Viral infection may induce autoimmunity due to antigenic mimicry


Immunity to parasites
Immunity to Parasites of specific antibodies;

  • Stimulate a number of immunological defense mechanisms

  • Both humoral and cellular responses

  • Immune response depends on the stage and the type of infection

  • Most parasites pass through a complicated life cycle


Features of Parasitic infection: of specific antibodies;

1- Infect large number of people

2- Parasitic infection have common features

Varity and large quantity of Ag

Ability to change their surface Ag

Complicate life cycle

Different mode of entry

3- Most parasites are host specific

4- Host resistance to parasite may be genetic

5- Many parasitic infections are chronic


Effector mechanisms by immune cells
Effector mechanisms by Immune cells of specific antibodies;

MACROPHAGES

  • Provide strong defense against small parasites

  • Secrete factors that kill parasites without ingestion

  • Secrete cytokines that activate other immune cells

  • Synthesize nitric oxide that act as parasite toxin

  • Activation of macrophages is a general feature of early stage of infection


NEUTROPHILS of specific antibodies;

  • Can kill large and small parasites

  • Phagocytic activation

  • Have granules that contain cytotoxic proteins

  • Have Fc and complement receptors >> ADCC

    PLATELETS

  • Cytotoxic activities against larval stages

  • Activation are enhanced by cytokines


EOSINOPHILS of specific antibodies;

  • Characterize parasitic infection

  • Thought to be specific against tissue parasites

  • Limit migration of parasites through the host

  • Less phagocytic than neutrophils

  • Act in accordance with mast cells


Role of t cells
Role of T cells of specific antibodies;

  • The type of T cells involved is determined by the type and the stage of the infection

  • Cytokines enhance protective immunity against intracellular parasites

  • T helper 2 cells are essential for the elimination of intestinal worms


Role of antibodies
Role of Antibodies of specific antibodies;

  • Parasites induce production of specific and non specific Abs

  • Antibodies have several functions on parasites

    -Act directly on protozoa

    -Block attachment to host cells

    -Important for Phagocytosis


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