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This study identifies a previously overlooked subset of immune cells in human blood, termed the "unclassified subset" (UCS), which are TLR2-positive but lack typical monocyte markers CD14 and CD16. These cells express CD163 and phenotypically resemble dendritic cells rather than monocytes, and are significantly reduced in multiple myeloma patients compared to healthy individuals. The research demonstrates that gating strategies using TLR2 to identify monocytes may inadvertently include CD163-positive CD1c-positive dendritic cells, challenging current classification methods.
Why it matters
The decreased levels of these CD163-positive dendritic cells in multiple myeloma patients may contribute to immune system dysfunction in this cancer. This finding could lead to improved diagnostic approaches and potential therapeutic targets for restoring immune function in multiple myeloma, while also highlighting the need for more precise cell identification methods in immunology research.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Background: Strategies to define human monocytes by flow cytometry vary considerably across studies. Recently, toll-like receptor 2 (TLR2) has been proposed as a marker to identify ” all monocytes ”in human peripheral blood. However, the TLR2-defined monocytes also contained a previously ignored TLR2posCD14dim/negCD16neg population, which we termed the unclassified subset (UCS). Methods: Peripheral blood mononuclear cells (PBMCs) from healthy donors and patients with multiple myeloma (MM) or monoclonal gammopathy of undetermined significance (MGUS) were analyzed by multiparameter flow cytometry using TLR2pos gating. PBMCs from additional healthy donors were analyzed to characterize the UCS population, including the impact of using either TLR2pos or a negative selection-based gating strategy. Results: The TLR2pos CD14dim/neg CD16neg UCS population was present in healthy controls, MGUS, and MM patients. The UCS expressed the monocyte-macrophage scavenger receptor CD163 and was significantly reduced in MM patients compared to healthy donors (P<0.002). Further phenotypic characterization in healthy blood donors revealed that approximately 80% of UCS cells expressed CD163 at levels comparable to classical monocytes, yet phenotypically resembled CD163pos dendritic cells (DCs). Importantly, gating strategies influenced the composition of the UCS: negative selection-based gating captured all DC subsets, whereas TLR2pos gating primarily included CD1cpos DCs that were highly CD163pos. Conclusions: These findings demonstrate that circulating CD163pos CD1cpos DCs are included in the TLR2pos cell population previously described as exclusively monocytes, highlighting the impact of gating strategy on monocyte subset identification. Further, the lower level of TLR2pos CD14dim/neg CD16neg CD163pos cells in MM patients may represent decreased levels of circulating DCs that may contribute to the immune dysregulation in this disease.