Background: Peripheral blood monocytes can be subdivided into different subsets based on the CD14/CD16 surface characteristics. Monocytes are a major source of cytokine secretion of pro-inflammatory immune responses, whereas CD16⁺ monocyte subsets can also contribute to persistent inflammation in the context of chronic diseases. However, the regulation and cellular characteristics of circulating monocyte subsets in patients with chronic otitis media (COM), one of the largest public health burdens, remains largely unknown. Materials and Methods: In this study, we analyzed individual distributions of circulating monocyte subsets and associated protein expression levels of adhesion protein and chemokine receptors CD11a (integrin-α L; LFA-1), CD11b (integrin-α M; Mac-1), and CD11c (integrin-α X), CX3CR1 (CX3CL1 receptor), as well as checkpoint molecule PD-L1 (programmed cell death ligand-1), in a gender-balanced cohort of 14 patients with chronic otitis media using flow cytometry, especially in view of the therapeutic impact of the natural plant-derived monoterpene oxide 1,8-Cineol. Furthermore, using the human monocyte cell line THP-1 as a model, we investigated the influence of anti-inflammatory 1,8-Cineol on monocytic cytokine secretion patterns using human cytokine arrays and ELISA measurements. Results: The data revealed significantly elevated expression levels of all analyzed adhesion molecules in certain monocyte subsets in COM patients; CX3CR1 was especially significantly down-regulated in response to 1,8-Cineol administration. Moreover, the data revealed significantly increased monocytic PD-L1 expression levels in circulating classical and intermediate monocyte subsets from COM patients compared to healthy donors, but also a significant decrease in PD-L1 in intermediate monocytes upon 1,8-Cineol therapy compared to the pre-treatment situation. Furthermore, the increased secretion of cytokine CXCL10 by THP-1 monocytes in response to LPS was found to be strongly attenuated by 1,8-Cineol. Plasma levels of CXCL10 were also significantly increased in COM patients, but no significant differences between the pre and post 1,8-Cineol situation were observed. Conclusions: The present study revealed new insights into the bioactive anti-inflammatory effects of 1,8-Cineol in terms of monocyte adhesion and immune regulation. Our data suggest the potential role of cytokine CXCL10 in COM development and maintenance, which is also involved in the activity of its concomitant disease, rheumatoid arthritis.

Tobacco smoking is closely associated with pro-inflammatory immunological alterations, whereas regular physical exercise is well known to lower systemic inflammations and related immune cell activities. The combined effects of smoking, nicotine pouch use, vaping, and exercise on individual immunological responses remain incompletely understood, especially in view of alternative nicotine delivery systems. In this study, we analyzed the immediate impact of different nicotine sources on exercise monocyte subsets in 16 human subjects using a four-arm cross-over design. Distribution of circulating CD14/CD16 monocyte subsets and expression of the monocytic checkpoint molecule PD-L1 (programmed cell death ligand-1) were analysed via whole blood flow cytometry measurements. Plasma cytokines were evaluated using membrane-based cytokine arrays and enzyme-linked immunosorbent assays (ELISA). Data revealed significant distributions of circulating monocytes subsets in response to nicotine consumption and physical stress. In contrast, exercise-driven increased monocytic PD-L1 was clearly attenuated following the consumption various nicotine delivery systems. Furthermore, significantly increased plasma growth hormone levels were detected in response to physical stress in combination with cigarette consumption. Our data clearly illustrates a significant influence of nicotine consumption on the cellular characteristics of circulating monocyte subsets and on proper exercise-driven immune responses within a short period of time, which makes the widespread trivialization of alternative nicotine sources questionable.