An introduction to immunology and immunopathology

Passive vs. active immunization

Acquired immunity is attained through either passive 

or active immunization. Passive immunization refers 

to the transfer of active humoral immunity, in the 

form of “ready-made” antibodies, from one individual 

to another. It can occur naturally by transplacental 

transfer of maternal antibodies to the developing 

fetus, or it can be induced artificially by injecting a 

recipient with exogenous antibodies that are usually 

manufactured for this purpose and that are targeted 

to a specific pathogen or toxin. The latter is used 

when there is a high risk of infection and insufficient 

time for the body to develop its own immune 

response, or to reduce the symptoms of chronic or 

immunosuppressive diseases.

Active immunization refers to the production of 

antibodies against a specific antigen or pathogen 

after exposure to the antigen. It can be acquired 

through either natural infection with a microbe or 

through administration of a vaccine that can consist 

of attenuated (weakened) pathogens, inactivated 

organisms or specific proteins or carbohydrates known 

to induce immunity. Effective active immunization 

often requires the use of “adjuvants” which improve 

the ability of the immune system to respond to antigen 

injection.

Immunopathology

As mentioned earlier, defects or malfunctions in 

either the innate or adaptive immune response can 

provoke illness or disease. Such disorders are generally 

caused by an overactive immune response (known as 

hypersensitivity reactions), an inappropriate reaction 

to self (known as autoimmunity) or ineffective immune 

responses (known as immunodeficiency).