Britannica Sources used in this answer

How do monocytes become macrophages in connective tissue?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Collagenous fibers — connective tissue Randomly oriented collagenous fibers of varying size in a thin spread of loose areolar connective tissue (magnified about 370 ×).

Monocytes are produced in the bone marrow and circulate in the blood before migrating into tissues, including loose connective tissue. Once they enter these tissues, they undergo a process of differentiation to become macrophages.123

This transformation is guided by local environmental signals, specifically cytokines and growth factors. In the presence of factors such as macrophage colony-stimulating factor (M-CSF), monocytes are stimulated to develop into highly phagocytic macrophages. Once differentiated, these cells act as mobile scavengers, essential for engulfing pathogens, clearing cellular debris, and supporting tissue repair.13