Examination of Synovial Fluid

Enhancement of crystal induced neutrophil responses by opsonisation of calcium pyrophosphate dihydrate crystals

OBJECTIVES

Little is known about the effect on crystal induced neutrophil responses of the opsonisation of calcium pyrophosphate dihydrate (CPPD) (triclinic) crystals with components of serum and plasma. The purpose of this study was to determine the effects of precoating CPPD crystals with plasma, serum, complement depleted serum, and IgG on a full range of crystal induced neutrophil responses (calcium mobilisation, chemiluminescence, superoxide anion production, non-cytolytic lysosomal enzyme release, and leukotriene synthesis).

METHODS

Crystals were precoated with IgG, serum, plasma, or complement depleted serum (heated at 56 degrees C), incubated with neutrophils and the responses monitored with time. Measurement of the extent of neutrophil association with crystals was based on monitoring the decrease in fluorescence intensity of supernatants when crystals and diphenylhexatriene labelled neutrophils were allowed to settle under gravity.

RESULTS

Precoating CPPD crystals with IgG, plasma, and serum significantly enhanced chemiluminescence, superoxide anion generation, increases in cytosolic free calcium levels, and non-cytolytic lysosomal enzyme release by neutrophils compared with uncoated CPPD crystals. The enhancement of neutrophil responses by crystals coated with complement depleted serum was less pronounced. The increased neutrophil responses induced by CPPD crystals coated with IgG might have been due to the observed increase in the association of IgG coated crystals with neutrophils.

CONCLUSIONS

These data show that there is a marked potentiation of all neutrophil responses to IgG, plasma, and serum coated CPPD crystals. It is suggested that the adsorption of synovial fluid proteins, including IgG and C3b, to CPPD crystals in vivo, results in the opsonised crystals becoming a potent neutrophil stimulant and inflammatory agent.

Methods of assessing the synovial fluid cell count

We have compared a rapid side-room testing strip and an automated cell counter with the conventional haemocytometer counting chamber as methods for assessing the synovial fluid cell count. The testing strip was shown to be very sensitive in detecting esterases derived from granulocytes, but to the experienced clinician it offered little clinical advantage over naked-eye judgement. The automated counter provides a fast and reliable alternative to the haemocytometer and in situations where an accurate cell count is required it could replace the haemocytometer.