An assessment of the interaction between human neutrophils, hydroxyapatite and dichloromethylene bisphosphonate in vitro: an electron microscopic and chemiluminescence study.

The potentially destructive effects of neutrophils, following particulate stimulus such as by hydroxyapatite (HA) crystals, may be pertinent to the progression of some inflammatory diseases, including rheumatoid arthritis. This study was designed to examine the interaction between pure hydroxyapatite particles and human neutrophil granulocytes by transmission electron microscopy and chemiluminescence (CL). The influence of dichloromethylene bisphosphonate (clodronate) in this model was investigated. Neutrophils convincingly phagocytosed HA particles within 15 min and a high CL response was elicited by the zymosan stimulated CL reaction. Clodronate alone appeared to have little effect on the cell morphology or CL. When HA was combined with clodronate, phagocytosis was more rapid, and the zymosan-stimulated CL was 50% of that of the HA group. The results demonstrate neutrophil phagocytosis of HA particles and subsequent cellular activation, which may play a role in the pathogenesis of tissue damage and suggest that the anti-inflammatory role of clodronate should be further investigated.