Two main subpopulations of human blood monocytes are distinguished on the basis of CD14 and CD16 expression: the major population with enhanced expression of CD14 (CD14++ monocytes) and the minor one with a weak expression of CD14 coexpressing CD16 (CD14+/CD16+ monocytes). As monocytes and macrophages are involved in antitumor response of the host, we assessed the ability of CD14+/CD16+ monocytes to produce cytokines (intracellular expression, release) and reactive oxygen and nitrogen (ROI, RNI) intermediates following stimulation in vitro with tumor cells.
Materials and methods
Monocytes were isolated by elutriation and their subpopulations by FACS sorting. Monocytes and their subpopulations were cocultured with tumor cells. Cytokine (TNF-α, IL-12, and IL-10) production was assessed by determination of intracellular protein expression by flow cytometry, and release by ELISA. ROI induction was detected by chemiluminescence and O2− production by flow cytometry, whereas RNI by intracellular expression of inducible NO synthase (iNOS) and nitric oxide (NO) release assessed colorimetrically.
Results
CD14+/CD16+ monocytes stimulated with tumor cells showed significantly enhanced production of TNF-α, IL-12p40, IL-12p70 (intracellular expression, release), whereas little IL-10 release was observed. CD14+/CD16+ subpopulation did not produce ROI, but showed an increased iNOS expression and NO release. CD14+/CD16+ monocytes also exhibited enhanced cytotoxic and cytostatic activities against tumor cells.
Conclusions
CD14+/CD16+ cells constitute the main subpopulation of blood monocytes involved in antitumor response as judged by enhanced production of proinflammatory cytokines, RNI, and increased cytotoxic/cytostatic activity.
