Phagocytic activity of blood monocytes in response to methicillin-resistant strains of Staphylococcus aureus

Current study performed to estimate the phagocytic activity of blood monocytes of varying phenotypes exposed to MRSA and MSSA strains.  Objects: Blood monocytes were collected from 25 healthy adults (age: 25–45 years). Live suspensions of MRSA/MSSA strains were used at concentration of 106 colony-forming units (CFU)/mL.  Metods. Phagocytic functions were estimated by using fluorescein isothiocyanate (FITC)-labelled MRSA and MSSA strains followed by running flow cytometry on FC 500 series flow cytometer (Beckman Coulter, USA). Whole peripheral blood cells were directly labelled with immunofluorescently tagged monoclonal CD14-PE/CD45-ECD/HLA-DR-PC5/CD16-PC7 antibodies (Beckman Coulter, USA). Respiratory burst intensity was evaluated in monocytes by measuring activity of lucigeninand luminol-dependent spontaneous and induced chemiluminescence. Monocytes were induced by using live suspension of MRSA/MSSA strains at a concentration of 106 CFU/mL. Results and discussion. While studying luminol-dependent monocyte activities after exposure to MRSA vs. MSSA, it was observed a 3.5-fold decreased curve square, whereas lucigenin-dependent chemiluminescence was increased by 6-fold. Compared to MSSA exposure, index of activation (IA) was decreased by 1.1-fold in response to MRSA exposure that was confirmed by lowered release of reactive oxygen species (ROS) from monocytes in response to MRSA exposure. Moreover, IRSS increased by 1.3-fold upon MRSA exposure. Examining monocyte oxygen-independent phagocytosis against MRSA vs. MSSA revealed significantly increased phagocytic number and concomitantly decreased phagocytic index. An evaluation of the activities of various monocyte subsets in response to MRSA vs. MSSA revealed increased phagocytic index by 1.5-fold for CD14^lowCD16⁺ and CD14⁺CD16⁺ monocyte subsets as well as 3-fold for CD14⁺CD16^– monocytes. Counts for all phagocytic subsets were decreased (1.4-, 1.5- and 4-fold for CD14^lowCD16⁺, CD14⁺CD16⁺ and CD14⁺CD16– monocytes, respectively). To summarize, intensity of the respiratory burst was lowered upon MRSA exposure and percentage of monocyte subsets. Overall deficiency of superoxide anion production was observed in response to MRSA. In contrast, oxygen-independent event revealed phenotypic changes in frequency of peripheral blood monocytes upon MRSA exposure. We observed that CD14⁺CD16^– classical monocytes were more rapidly activated. Conclusion. Thus, we concluded that CD14⁺CD16^– monocytes became more rapidly activated but exhibited less effective phagocytosis, whereas CD14⁺CD16⁺ and CD14^lowCD16⁺ monocytes were more slowly activated and demonstrated stronger phagocytic activity.