Background: Monocytes/macrophages may be affected by tumour cells via cell-to-cell contact, soluble factors and by tumour-derived microvesicles (TMV). Previous observations indicate that TMV interact with monocytes and alter their immunophenotype and activity. This study was designed to determine interactions of TMV with subpopulations (CD14++CD16– and CD14+CD16++) of human monocytes. Methods: Engulfment of TMV by subsets of monocytes was analysed by flow cytometry. Moreover cytokine release and production of reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI) by CD14++CD16– and CD14+CD16++ cells after TMV stimulation was determined. Results: It was found that TMV are engulfed more efficiently by CD14++CD16– than CD14+CD16++ cells. TMV-activated CD14++CD16– cells produce more ROI and interleukin -10 (IL-10) than CD14++CD16+. CD14+CD16++ cells following TMV stimulation showed an increased release of tumour necrosis factor alpha, IL-12p40 and RNI. Conclusion: TMV significantly modulate biological activity of monocyte subsets with a pattern similar to tumour cells. Therefore, TMV mimic the activating effect of tumour cells on monocytes as assessed by release of cytokines, ROI and RNI
