Circulating immune complexes of calves with bronchopneumonia modulate the function of peripheral blood leukocytes: In vitro evaluation

•Calf bronchopneumonia is accompanied with an increased level of CIC.•CIC modulate adhesion and ROS synthesis in peripheral blood leukocytes in vitro.•CIC modulate proliferation of peripheral blood mononuclear cells in vitro.•The modulatory effects of CIC are dependent on the maturity of leukocytes' donors.•The effects of CIC are dependent on the activation state of the responder leukocytes.

In this work we studied if circulating immune complexes (CIC) of calves with bronchopneumonia have the capacity to modulate function of peripheral blood leukocytes of healthy cattle.CIC of three month old calves (6 healthy and 6 diseased) were isolated by PEG precipitation. Peripheral blood mononuclear cells (MNCs) and granulocytes from healthy calves and cows were the CIC responder cells in in vitro tests.The most remarkable increase of adhesiveness to polystyrene and ROS synthesis (assessed by NBT test) was detected in cows' granulocytes stimulated with CIC of diseased calves. Results of MTT test showed that CIC of both healthy and diseased calves reduced granulocytes' viability. The strongest effect of inhibition of cows' granulocytes resulted from CIC of diseased calves. CIC only moderately reduced spontaneous viability of calves' MNCs. Again, the strongest effect of CIC isolated from diseased calves was observed. In contrast to the low impact of CIC on non-stimulated cells, their inhibitory effect on viability of mitogen stimulated MNCs was very strong. With CFSE assay we showed that both types of CIC stimulated spontaneous, but inhibited mitogen induced proliferation of calves' MNCs. Propidium iodide staining reviled that CIC increased apoptosis/necrosis of both non-stimulated and mitogen stimulated MNCs.CIC of both healthy and diseased calves modulated the function of peripheral blood MNCs and granulocytes, but a stronger effect of CIC of diseased calves was shown. The age of the donors (calves or cows) of the responder cells, and the activation state of these cells, were also of influence.