Aim. To evaluate the platelet (Pl) reactivity to the platelet-activating factor (PAF), as well as their ability to form platelet-leukocyte aggregates (PLA) against the background of use of non-steroidal anti-inflammatory drugs and antibiotics in patients with chronic obstructive pyelonephritis (COPN).
Materials and Methods. The study included 43 patients, of which 26 – with COPN in the remission phase and 17 patients COPN in the attack phase. Platelets were isolated by centrifugation from citrated peripheral blood. The Pl aggregation was evaluated on ChronoLog aggregator (USA) using stimulation with PAF at EC50 concentration. The number of PLA was assessed after blood smear staining by Romanowsky-Giemsa method.
Results. In the attack phase of COPN, a high residual Pl reactivity to PAF was revealed. At the same time, in the phase of recurrence of the disease Pl form more PLA, with predominant concentration of neutrophils and monocytes. For the remission phase of COPN, the variability of the Pl reactivity to PAF is typical, which reflects the features of the realization of a chronic inflammatory reaction. In 10 (38.5%) patients with COPN in the remission phase with a higher residual Pl reactivity, the stimulating effect of PAF was manifested by an increase in the number of platelet-neutrophilic and platelet-monocyte aggregates, whereas in 16 (61.5%) patients with low residual reactivity – by an increase in the number of platelet-lymphocytic aggregates.
Conclusions. The increase in the number of aggregates that provide the recruitment of neutrophils and monocytes to the focus of inflammation during remission of COPN can be a predictor of the transition of chronic inflammation to the acute phase.

Keywords: platelet-activating factor, paracrine regulation of inflammation, residual platelet reactivity, platelet-leukocyte aggregates