Question

The first line of defense in the immune system is provided by

• A. skin and mucous membrane
• B. lymphocytes
• C. the complement system
• D. hormones and enzymes

Answer 1

The correct option is A skin and mucous membrane

Innate immunity acts as the first line of defence against any foreign pathogen; it is the primary defence against entry of any non-self molecule/antigen into the host. Innate defence acts as the initial response and activates immediately to obstruct the invasion of the microorganisms that are harmful. There are many different types of barriers that act as the first line of defence, such as physical barriers, chemical barriers, cellular barriers etc. that a body adapts to fight the entry of pathogens.

Physical barriers include skin, mucus, mucous membranes of gastrointestinal tracts, respiratory tract, urogenital tract etc. Physical barriers actually distinguish between the internal and external environment of the body and tissues, and hence restrict the entry of any foreign pathogen inside the body or tissue. These barriers act as the first line of defence, once these are breached then the second line of defence or acquired immunity comes into play and helps eradicate the invaders/pathogens as they are more specific, unlike innate immunity.

Once the pathogens enter the body by breaching the first line of defence, then the inflammatory response, activation of the complement system, activation of other chemokines, enzymes and hormones may occur as the result of the action of the second line of defence or acquired immune response.