Immunology basics

1. Immunology
The immune system recognizes our enemies (which are
mainly micro organisms) and protect our body against
them
Immunity is the ability to resist or overcome infection or
invasion of any other external harmful agents
The two types of Immunity are Innate and Adaptive

3. Innate immunity is the first line of defense. It is
inborn.
It prevents the entry of harmful agents by putting
up barriers (eg. Skin) or destroy them with
specialized cells (eg. Macrophages).
The pathogens have some molecules (not present
in our normal cells) called Pathogen Associated
Molecular Patterns (PAMPs) and the
macrophages have receptors termed Pattern
recognition receptors (PRS) to recognize them.
Innate immunity is Nonspecific and without
memory.

4. Adaptive immunity is the second line of defense.
It is acquired when the immune system confronts
pathogens / antigens (Active) or by directly getting the
secreted mediators of immunity esp. antibodies (Passive).
In practical terms:
- Active immunity means antibodies are produced in
our body against antigenic challenge ( Infection /
Vaccination )
- Passive immunity means receiving readymade
antibodies (From mother to child during fetal life
and breast feeding / therapeutic administration)
The cardinal features of adaptive immune responses are
specificity, memory and self discrimination

6. Immunity
Innate Adaptive
Active Passive
Cells having the Innate and adaptive functions can
interact each other. Mostly, when a pathogen or
antigen is encountered by the mediators of innate
immunity, they release certain cytokines which
induce inflammation and this in turn leads to the
recruitment of the mediators of adaptive immunity.

9. • Important Cellular Components
• Natural Killer Cells Innate
• Antigen Presenting or
Antigen Processing cells Innate and adaptive
• Macrophages
• T Cells
• B Cells Only adaptive
• Important Secreted Mediators
• Antibodies Adaptive
• Compliments
• Cytokines Innate and adaptive

10. • Macrophages engulf (eat) the pathogen and
digest them
• Natural killer cells destroy the pathogen by
releasing toxic substances
• Antigen presenting / Antigen processing cells
capture the pathogen / Antigen and process
them. The processed antigens (antigenic
determinants) are then presented to the T
cells and / or B cells.

11. • B cells are Bone marrow derived
lymphocytes and
• T cells are thymus derived lymphocytes.
• They are exclusively responsible for
recognizing and destroying antigens /
pathogens
• B cell destroy the antigens by producing
antibodies. This is termed humoral immunity
or antibody mediated immunity (AMI) and is
most effective in removing extra cellular
antigens.

12. • There are basically two types of T cells – Helper T cells (Th0)
which are CD4 cells and Cytotoxic T cells (Tc) which are CD8
cells
• Tc directly destroy the antigens (infected cells) by releasing
cytotoxins. This is termed as Cell Mediated Immunity (CMI)
and is very essential for removing Intra Cellular Antigens.
• On interaction with intra cellular antigen Th0 differentiate in
to Th1 helper cells which in turn help the Tc leading to CMI.
• On interaction with extra cellular antigens Th0 differentiate in
to Th2 helper cells which in turn help the B cells leading to
AMI