Failure of platelets to enhance aggregation of temperature-stabilized neutrophils: Effects of warming and of drugs

Polymorphonuclear leukocytes (PMNs) were isolated on a Ficoll-Hypaque gradient, suspended in modified Hank's buffer, and aggregated alone or in the presence of washed platelets (4 or 8/PMN). Platelets had no effect on formyl-methionyl-leucyl-phenylalanine (FMLP)-induced aggregation of PMNs that had been allowed to equilibrate at 37°C for 5 min after storage at room temperature. Pretreatment of platelets with an inhibitor of cyclooxygenase (ASA) or lipoxygenase (nordihydroguaiaretic acid, NDGA) produced no significant effect whereas pretreatment with an inhibitor of both enzymes (eicosatetraynoic acid) or of phospholipase (methylprednisolone sodium succinate) caused a modest but statistically-significant inhibition of PMN aggregation which appeared to be a direct effect on PMNs rather than through platelets.

The warming of PMNs from 0°C or 22°C to 37°C produced a spontaneous, reversible aggregation within 2 or 3 min, the extent of which was dependent on the degree of temperature change. This aggregation was enhanced by the presence of platelets in a ‘dose’ (count) dependent fashion. This enhancement was not decreased by any of the aforementioned drugs, in fact, the aggregation was augmented by all drugs, the difference being statistically significant for NDGA. Thus different mechanisms appear to be involved in spontaneous vs FMLP-induced aggregation. The role of platelets in PMN aggregation remains to be elucidated but the importance of controlling for the effects of temperature changes in such studies is self-evident.