Which one of the following acts as a cellular barrier to the entry of microorganisms in the human body?

The correct option is D

All of the above

The correct option is option D.

Explanation of correct option:

1. PMNLs (polymorphonuclear neutrophil leukocytes) play a critical protective role against a wide range of bacteria and other pathogens.
2. Monocytes are a type of white blood cell (leukocyte) that lives in our blood and tissues and hunts down and kills germs (viruses, bacteria, fungus, and protozoa) as well as remove infected cells.
3. Monocytes enlist the support of other white blood cells to treat and prevent illness.
4. Natural Killer (NK) Cells are lymphocytes that are linked to T and B cells and are produced from the same progenitor as T and B cells.
5. NK cells, on the other hand, are categorized as a group I Innate Lymphocytes (ILCs) and respond promptly to a variety of pathogenic stimuli as cells of the innate immune system.

Final answer: PMNL-neutrophils, Monocytes, Natural killer cells all act as a cellular barrier to the entry of microorganisms in the human body