The immune system can be split easily into two components:

Innate immunity:

Innate immunity is non-specific to pathogens, and consists of several barriers to minimise the chance of invasion by pathogens

Physical barriers:

                - Skin

                - Mucous membranes

Chemical barriers:

                - PH

                - Complement system

                - Interferons

Social barriers:

   - Waste sanitation

   - Clean water

Once the barriers presented to pathogens by the innate immune system have failed then the body’s defence becomes cellular and specific to the disease causing agent, through the production of antibodies.  

Adaptive Immunity:

Adaptive immunity can be actively acquired or passively acquired

Vaccination of a girl: an example of active immunity

 Active immunity:

This requires the body to react to the pathogen by producing antibodies, done by triggering an immune response. This can occur through contraction of a bacteria or virus or can be triggered purposefully through immunization. This exposure to the causative agent triggers immunological memory and so immunity, immunity can last years or can even be lifelong.

Passive immunity:

This is the transfer of antibodies into the body, providing immediate but short-lasting immunity to the pathogen, it can be acquired through two routes

  • Natural: This is the transfer of antibodies from mother to child via the placenta or through breast milk.
  • Artificial: This is the transfer of antibodies into a patient artificially. It is usually done when an illness has a fast course of advancement, meaning there is not enough time for the body to mount its own defence and produce antibodies in response, an example of which would be the administering of antibodies after a toxin, such as tetanus, has been introduced into the body

The immune response is flexible and can be moderated depending on several factors:

  • Nature of the antigen
  • The dose of the antigen
  • Immunological memory
  • Genetic predisposition of the infected individual



Diagram courtesy of Wikimedia Commons

Picture courtesy of Wikimedia Commons

Immunology, David K. Male, Jonathan Brostoff, Ivan Maurice Roitt, David B. Roth, Elsevier Health Sciences, 2006

Immunology: an illustrated outline, David K. Male, Elsevier Health Sciences, 2004