Regulatory Effects of CD14 ⁺ CD16 ⁺⁺ Slan ⁺ Monocytes on Classical Monocytes and T Lymphocytes in Response to Inflammatory and Phagocytic Stimuli

Background CD14 + CD16 ++ 6‐sulfo LacNAc (Slan) + monocytes represent a specialized nonclassical subset with reported pro‐inflammatory and regulatory features. However, their capacity to modulate classical monocytes and T lymphocytes under apoptotic and inflammatory conditions remains incompletely defined. Methods We employed a coculture reconstitution model using flow cytometry—sorted CD14 + CD16 ++ Slan + monocytes and CD14 ++ CD16 - Slan − classical monocytes at defined ratios. Cultures were stimulated with lipopolysaccharide (LPS) or K562‐derived apoptotic bodies (ABs). Monocyte surface marker expression was evaluated by flow cytometry, and cytokine concentrations were quantified using multiplex bead‐based assays. The impact of Slan + monocytes on CD3 + T cell proliferation and cytokine production was assessed following monocyte–T cell coculture. Results CD14 + CD16 ++ Slan + monocytes exhibited enhanced uptake of ABs and distinct phenotypic modulation upon stimulation. Increasing proportions of Slan + cells induced higher HLA‐DR and CCR5 expression on classical monocytes. LPS stimulation promoted TNF, IL‐12, IL‐6, and CCL2 production, whereas AB exposure favored IL‐10 and IL‐17 accumulation. In coculture assays, Slan + monocytes reduced CD4 + and CD8 + T cell proliferation and altered T cell cytokine profiles in a stimulus‐dependent manner. Conclusion CD14 + CD16 ++ Slan + monocytes exert a dose‐ and context‐dependent modulatory effect on classical monocytes and T lymphocytes in vitro, displaying both inflammatory and regulatory properties depending on the stimulus. These findings highlight their functional plasticity within the human monocyte compartment.