IMMUNITY
INTRODUCTION
• Immunity : Defence capacity of the body
to combat diseases counter infection.
Immune System: Molecules, cells,
tissues and organs which provide non-
specific and specific protection against,
Microorganisms, Microbial toxins, Tumor
cells.
The
The Immune
Immune System
System
3 Major Functions
1. Protection from disease
2. Removal of dead /damaged tissues &
cells
3. Recognition & removal of abnormal
cells
Types Of Immunity
• Inborn or innate immunity: It is present at birth;
This is our First Line Of Defense.
• Acquired or specific: It is not present at birth
but becomes part of our immune system as the
lymphoid system develops.
• 1970: WHO defined immunity as immune
response to antigen.
• Humoral ( activation of B-lymhocytes)
• Cellular (by activation of T-lymphocytes
Cells Involved in Immunity
Innate Immunity
Innate Immunity
Defensive mechanisms include :
1) Innate immunity (Natural or Non specific)
2) Acquired immunity (Adaptive or Specific)
Cell-mediated immunity Humoral immunity
Component of Innate Immunity
Innate Immune system
First line Second line
1) Mechanical barriers A- cells
2) Chemical & biochemical inhibitors 1- Natural killer
3) Normal flora 2- Phagocytes
B- Soluble factors
C- Inflammatory barriers
Important components of innate immunity
Factors that limit entry of microorganisms into the body
Factor Mode Of Action
-Keratin layer of intact skin -Acts as mechanical barrier
-Lysozyme in tears and other secretions -Degrades peptidoglycan in bacteria
cell wall
-Respiratory cilia -Elevate mucus containing trapped
organisms
-Low pH in stomach -Retards growth of microbes
-Surface phagocytes -Ingest and destroy microbes
---Normal flora of throat, colon -Occupy receptors which prevent
colonization by pathogens
Main Components of Innate Immunity that
contribute to humoral ( antibody-mediated )
immunity and cell mediated immunity
Humoral Cell mediated
Immunity Immunity
Innate
Complement Macrophages
Neutrophil Natural killer
cells
Specificity Of The Immune
Response
-Recognition of the foreign organisms by specific
immune cells
-Activation of these immune cells to produce a specific
response (eg,antibodies)
-Response that specifically targets the organisms for
destruction
Important features Of Innate Immunity
Specificity Effective immediately Improves Has
after exposure to After Exposure memory
microbe
Nonspecific Yes in No No
minutes
Active and Passive Immunity
• Active immunity is resistance acquired after
contact with
foreign antigens, eg, microorganisims
• This contact may consist of :
Clinical or subclinical infections
• Immunization with live or killed infectious agents
or their antigens.
• Exposure to microbial products (eg, toxins and
toxoids)
Example
• Active immunity would be resistance to a
common cold. Due to previous exposure,
a person has some antibodies against the
common cold virus. Due to the presence
of antibodies, the person is able to fight
the cold off faster and more efficiently than
if they had no prior exposure.
Passive immunity
• Passive immunity is provided when a
person is given antibodies to a disease
rather than producing them through his or
her own immune system. A newborn baby
acquires passive immunity from its mother
through the placenta.
Immunogen and Antigen
• When foreign substances are introduced into the body,
they lead to anti-foreign substance
• ( Anti-body ) formation
• Immunogenic when they are able to produce specific
immune response; that they will stimulate immune cells
and then give rise to immunological reaction (Humoral
or cellular).
• Antigenic substances cannot directly yield immune
response, but need some help by some proteins) and
then
• They can react with antibodies.
• All immunogens are antigenic but not all antigens
are immunogenic
