A type of leukocyte polymorpho-nuclear leukocytes (PMNL-neutrophils) belongs to which type of barrier under innate immunity?

Cellular barrier.

The correct answer is Option (2) –Cellular barrier.

Innate immunity is a non-specific defense mechanism that is present in an individual from birth. It consists of various types of barriers designed to prevent the entry of foreign agents into the body. Innate immunity encompasses four main categories of barriers:

(i) Physical Barriers: The skin serves as the primary physical barrier, effectively preventing the entry of microorganisms. Additionally, mucus coats the epithelium lining the respiratory, gastrointestinal, and urogenital tracts, aiding in the capture and entrapment of microbes attempting to enter our body.

(ii) Physiological Barriers: Various physiological factors act as barriers to microbial growth. These include the acidic environment in the stomach, saliva in the mouth, and tears produced by the eyes, all of which deter the proliferation of microbes.

(iii) Cellular Barriers: The immune system deploys certain types of white blood cells, such as polymorphonuclear leukocytes (PMNL-neutrophils), monocytes, natural killer cells (a type of lymphocyte) in the bloodstream, and macrophages in tissues. These cells have the ability to phagocytose (engulf and destroy) microbes, providing an essential defense mechanism against invading pathogens.

(iv) Cytokine Barriers: In response to viral infections, infected cells release proteins called interferons. These interferons play a vital role in protecting non-infected cells from further viral infections, acting as a crucial part of the innate immune response.