Crescents are derived from-

The glomeruli show cellular proliferation outside the capillary loops, sometimes in association with segmental capillary necrosis, breaks in GBM, and deposition of fibrin in Bowman's space. These distinctive proliferative lesions outside the capillary loops are called crescents owing to their shape as they fill Bowman's space. Crescents are formed both by the proliferation of epithelial cells and by the migration of monocytes/macrophages into Bowman's space. Smaller numbers of other types of leukocytes also may be present. Ref: ROBBINS BASIC PATHOLOGY 10th ed Pg no: 563