Immunology Introduction

\ $Pathogenic organism$ : the organism able to produce disease.

}}Bacteria Divisions according to degree of Pathogenicity}}

%%Pathogenic bacteria%%: bacteria live in a host and cause tissue damage and disease
%%Commensal bacteria%%: live on surface of host body, do not cause disease = normal flora, sometimes benefit as they compete with pathogen and inhibit their growth.
%%Saprophytoc bacteria%%: live free in nature, do not cause disease
%%Opportunistic bacteria%%: when commensal bacteria cause disease, if hosts defense decreased or if it changes its habitat.

\ $Pathogenicity:$ the ability of an infectious agent to cause disease.

$Virulence$ : measure the quantitative ability of pathogen to cause disease.

}}Symbiotic Relationships}}

$Commensalism$ : one of the organisms benefits without harming the other

$Mutualism$ : both organisms benefit (e.g. E.Coli in intestines produce Vit. K and some B vitamins)

$Parasitism$ : one organism benefits at the expense of the other

}}Infection}}

the process by which parasite enter the body (bacteria, virus, fungus).

The result may be:

$Sub-clinical or silent infection:$ infection without manifest clinical disease
$Clinical disease$ : signs and symptoms

Requirement steps of Infection to occur

Source of infection
Mode of transmission
Multiplication inside host
Site of exit from host

\ $Vertical transmission:$ pathogen can cross the placenta, transmission during birth (post natal)

}}Spread of Infection}}

@@Human@@: human body, carriers
@@Animal@@: zoonosis (diseases that occur primarily in wild and domestic animals, and can be transmitted to humans (e.g rabies))
@@Nonliving Reservoirs@@: soil, water

}}Reservoirs of Infection}}

Contact transmission
Vehicle transmission
Vectors

Contact transmission

@@Direct contact@@: person - person
@@Indirect contact@@: person - nonliving object
@@Droplet transmission@@

Vehicle transmission

Waterborne transmission
Airborne transmission
Blood, body fluids, drugs and intravenous fluids

Vectors

animals that carry pathogens from one host to another (mostly arthropods)
Mechanical transmission: via simple contact
Biological transmission: via bites and blood

}}Carriers}}

Healthy individual carries pathogenic organism without clinical manifestation and can transmit this organism to other individual.

}}Bacterial virulence factors}}

@@certain structures or product that helps bacteria to cause disease@@

Virulence factors:

adherence factor
invasive factor
anti-phagocytic factors
intracellular pathogenicity
enzymes
antigenic heterogeneity
toxic production

\ @@Anti-phagocytic factors:@@ factors that prevent phagocytosis

capsule (best)
protein A of staph.
M-protein of strept.

}}Toxin production}}

%%Exotoxin%%: produces gram positive ( + )

%%Endotoxin%% produces gram negative ( - ) on its cell wall

}}Immunogens or Antigens}}

$Immunogens$ : any foreign substances which can stimulate immune response
$Haptens (Incomplete antigen):$ low molecular weight substances not capable of inducing an immune response. When they are coupled to a larger carrier protein they become capable of inducing an immune reponse.
$Epitopes (Antigenic determinants):$ part on antigen that bind with antibody or immune cell receptors. = antigen binding site

}}Antigen characters that induce immune response (to be immunogenic)}}

Foreignness
Molecular size
Protein
Methods of Administration of Antigen
$Adjuvant$ * substances when mixed with an antigen before its administration will increase the immune response to that antigen

}}Types of Antigens}}

bacterial
viral
superantigens
human tissue antigens (isoantigens): * %%Blood group antigens%%: A, B and D * $Histocompatibility antigens$ : glycoprotein on membranes of tissue cells. * called: Histocompatibility complex (MHC) antigens or human leukocytic antigens (HLA)

Two classes of MHC:

$MHC I:$ present on all nucleated cells and APCs

$MHC II$ : present on antigen presenting cells (APCs)

Antigen presenting cells (APCs)

dendritic cell
macrophages
B cell
T cell

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