BACTERICIDAL EFFECT OF HUMAN SERUM ON BORRELIA MIYAMOTOI, CAUSATIVE AGENT OF IXODES TICK-BORNE BORRELIOSIS

Abstract

Aim. In this paper we investigate the impacts of co-incubation of Borrelia miyamotoi with neutrophils. Materials and methods. Spirochetes B. miyamotoi, strain HT31, were incubated 3 hours at 37°C with neutrophils of healthy donors (5*106 cells/ml) in a 1:1 ratio. The incubation medium contained also non-immune serum of healthy blood donors (SHD) and, in some experiments, high-immune serum of patients recovered from ITBB-BM (S-ITBB-BM). The proportion of neutrophils that bound borrelia, as well as the number and viability (mobility) of free borrelia, was estimated by dark-field microscopy. Results. Free-swimming borrelia remain viable in SHD or heat-inactivated S-ITBB-BM, but about 10% of borrelia are associated with neutrophils. In S-ITBB-BM with neutrophils, the proportion of viable borrelia among free ones decreases by approximately 10% compared to S-ITBB-BM without neutrophils; in addition about 15% of bor-relia become bound by neutrophils. If chemoattractant fMLP was added, the proportion of neutrophils binding borrelia increases to 25%, and the proportion of immobilized non-bound bor-relia reaches 40%. Conclusion. Although neutrophils are able to destroy borrelia with or without direct contact, under model conditions the combined effect of blood neutrophils and high-immune human serum does not provide 100% elimination of B. miyamotoi.