Final answer:
Macrophages do differentiate from circulating blood monocytes, playing a vital role in the immune system by engulfing pathogens and debris, and signaling other immune cells to the infection site through cytokines.
Step-by-step explanation:
It is true that macrophages differentiate from circulating blood monocytes. Monocytes, which are a type of white blood cell, originate from myeloid stem cells and typically represent 2-8 percent of the total leukocyte count. Their key identifying features include a large size of 12-20 µm and an indented or horseshoe-shaped nucleus.
As part of the immune system, monocytes circulate in the bloodstream and lymph and enter infected tissue where they differentiate into macrophages. These macrophages play a crucial role in phagocytizing or engulfing pathogens, debris, worn-out erythrocytes, and other damaged cells. Furthermore, they release antimicrobial defensins and chemotactic chemicals, which attract other immune cells to the site of infection.
Macrophages come in two main forms: fixed macrophages, which reside permanently in tissues, and roaming macrophages, which move throughout the tissue fluid. When activated, macrophages can release cytokines, signaling proteins that recruit and activate other immune cells at the site of an infection.