Passive Immunization

The question describes a scenario where a person infected with a deadly microbe is given preformed antibodies to provide a quick immune response.

Let's analyze the different types of immunity mentioned:

• Active immunity: This develops when an individual's own immune system is stimulated to produce antibodies and memory cells in response to exposure to an antigen (either through natural infection or vaccination). This process takes time to develop but provides long-lasting protection.
• Cell-mediated immunity: This type of immunity involves T-lymphocytes directly attacking infected cells or activating other immune cells. It does not primarily involve the administration or production of free antibodies for immediate defense in this manner.
• Innate immunity: This is the non-specific, first line of defense present from birth (e.g., skin barriers, phagocytic cells, inflammation). It does not involve specific antibodies, either produced or administered.
• Passive immunity (or Passive immunisation): This occurs when an individual receives preformed antibodies from an external source, rather than producing them themselves. Examples include antibodies passed from mother to fetus/infant or the administration of antibody-containing serum (antiserum) as a treatment. This provides immediate, but temporary, protection because the recipient's immune system is not stimulated to create its own memory.

The scenario described – administering preformed antibodies for immediate protection against a deadly microbe – directly corresponds to the definition of Passive immunisation.