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

Abstract

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.