Question

Certain types of leukocytes (WBCs) like polymorphonuclear leukocytes (PMNL - neutrophils) and natural killer cells in the blood are cellular barriers, which provide innate immunity in humans.

Answer 1

Certain types of blood cells called leucocytes (WBC) like Polymorpho-Nuclear Leucocytes (PMNLs) or neutrophils and monocytes, natural killer cells (type of lymphocytes) as well as macrophages are the most important phagocytes that destroy the pathogens by phagocytosis. Since these immune cells work on the cellular level to protect a person from pathogen hence collectively form cellular barrier for innate immunity. Apart from these cells there is a physical barrier which includes skin and mucous membrane, Physiological barriers include body temperature and pH and there is also a cytokinin barrier that is effective in case of viral infections. All these are part of a person's innate immunity.