Answer:
The correct answer is - host immune system.
Explanation:
Monocytes are one of white blood cells or normally called leukocytes. Monocytes are the largest white blood cells and distinguished to the myeloid lineage dendritic cells and large monocytes known as the macrophages.
Monocytes are the cells that influence the adaptive immunity in the particular host that is experiencing the infection of foreign particles or antigen. It is a part of all vertebrate innate immune system.
Thus, the correct answer is - host immune system.