Monocytes, in conjunction with epithelium-derived factors, can act to facilitate which biological process?

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.

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.