Resorption of hydroxyapatite by osteoclast-like giant cells exposed to M-CSF and IL-4. Hydroxyapatite was stained black by Von Kossa staining. UG3 cells that had been cultured in the presence of M-CSF (100 ng/mL) and IL-4 (100 U/mL) had pericellular clear areas (A) resulting from hydroxyapatite resorption, whereas those that had been cultured in the presence of IL-3 (5 ng/mL) and IL-4 (100 U/mL) did not (B). Original magnification, 30-fold. Histochemical analysis was performed with cells obtained from three independent cultures.