Complete Overview of the Immune System
                     Complete 
Overview of the 
Immune System
What is immune system?
 The immune system is a system developed within our 
bodies to protect and eliminate harmful microorganisms 
and abnormal growth in the body.
 It has the ability to recognize and respond to an invading 
pathogen, allergen or toxin and distinguish self from non-
self
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Parts of the immune system
 The main parts of the immune system are white blood 
cells, antibodies, lymphatic system, spleen, bone marrow 
and thymus.
 There are two types of immune response– Innate and 
Acquired.
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First line of defense
 The skin, mucosa, cornea etc. are the physical barriers 
which act as the first barrier of defense against harmful, 
invading agents. 
 They are also a part of the immune system.
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Innate immunity
 Innate immunity is present at birth, it is the natural 
immunity for protection and does not require prior 
exposure to an antigen to recognize it.
 Antigen is any molecule which can be recognized by the 
immune system and stored in the immunological memory
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Acquired immunity
 Acquired immunity requires prior exposure to an antigen 
and it takes time to adapt against it when it attacks for the 
first time. The next attack will invoke a quick response 
against the antigen
 It includes Cell-mediated immunity and Humoral immunity
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Immune response
 For the immunity system to work successfully, there must 
be an efficient immune response.
 It requires activation, regulation and resolution against the 
foreign antigens.
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Immune system disorders
 There are some chances of having an overactive or 
underactive immune system, which are immune system 
disorders.
 Allergic diseases like asthma, sinusitis, food or insect sting 
allergies are due to overactive immune response
 Immunodeficiency or underactive response may be 
hereditary or due to diseases like HIV/AIDS.
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Immunization
 Commonly called vaccination, it is an artificial method of 
immune response generated by injecting a vaccine.
 Vaccines are specially treated bacteria or toxins, which 
makes the body produce antibodies to act against diseases 
in future.
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Changes with growing age
 As a person becomes older, their immune system 
weakens. It is not able to distinguish self from non-self 
easily, causing auto-immune disorders.
 T cells respond less quickly to antigens and Macrophages, 
which destroy bacteria and cancer cells become weaker.
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