diagnostic immunology n.
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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




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


The establishment of an infection depends on several factors:

  • Characteristics of the microorganism
  • Number of organisms
  • Mode of transmission (how and where they contact the host)
  • Stability of the organism (in and outside of the host)
types of defense systems

1- Immediate immune response

  • Complement
  • Phagocytosis
  • Natural Antibodies

2- Early immune response

3- Late immune response

the early ir
The Early IR
  • 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
  • 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
  • The first line of defense is NOT dependent on antigen recognition
    • Innate immunity
    • Complement activation
    • Phagocytosis
    • NK cells
Most bacteria are killed by phagocytosis:
  • 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
  • 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
Little is known about the precise mechanisms involved
  • Thought to be similar to those against bacteria

Fungi infection in human

Specific mycoses.

Subcutaneous mycoses.

Respiratory mycoses.

proposed mechanisms
Proposed mechanisms

Based on cell immunity:

T Helper cells


Activation of macrophages

Elimination of fungi

immunity to viruses
Immunity to Viruses
  • 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
  • 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;


Nk cells


mechanisms involving t cells
Mechanisms involving T cells

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
  • 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

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
  • 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:

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


  • 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
  • Can kill large and small parasites
  • Phagocytic activation
  • Have granules that contain cytotoxic proteins
  • Have Fc and complement receptors >> ADCC


  • Cytotoxic activities against larval stages
  • Activation are enhanced by cytokines
  • 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
  • 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
  • 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