Date: Monday, October 22, 2018
Session Title: Innate Immunity Poster
Session Type: ACR Poster Session B
Session Time: 9:00AM-11:00AM
Populations of monocytes in mice are distinguishable by expression of Ly6c. Ly6chi monocytes are associated with pro-inflammatory responses, while Lyc6lo are involved in lining and patrolling endothelial membranes. Both Ly6chi and Ly6clo monocytes can differentiate into macrophages and have been implicated in inflammatory arthritis and we have previously shown Lyc6lo monocytes are essential for development of serum transfer induced arthritis (STIA). In the present study we show that NR4A1-deficient mice, which have a marked reduction of circulating Ly6clo monocytes but retain Ly6clo monocytes attached to endothelial vessels, also develop arthritis. Thus, we postulate that Ly6clo monocytes may be a heterogeneous population with distinct functions (circulating vs patrolling).
Female NR4A1-/- and C57Bl/6 mice were bred in house to 8-10 weeks old. STIA was induced by intravenous (IV) administration of KBxN sera at 85µl/20g. Arthritis was measured using clinical score, and mean clinical scores of N=4 per group were calculated. Monocytes were depleted using IV administration of clodronate-loaded liposomes (Clo-Lip). PBS-loaded liposomes were used as a negative control. Mice were euthanized by CO2. Blood was collected by cardiac puncture and distal joints were collected following perfusion with PBS. Blood and joint monocytes were isolated by FACS and characterized by flow cytometry and RNA-sequencing (RNA-seq). Statistical analysis of disease and flow cytometry was carried out in GraphPad Prism. Statistical significance was considered at P ≤ 0.05.
NR4A1-/- mice displayed a significant reduction in Ly6clo monocytes in the blood compared to C57Bl/6 controls, although joint Ly6clo monocytes in the joint were not significantly reduced. No significant differences were observed between arthritis severity between genotypes. In C57Bl/6 mice, Clo-lip administration resulted in over 90% depletion of CD115+ blood monocytes, however over 35% of synovial monocytes remained, suggesting they are not in the circulation. Of these, Ly6chi and Ly6cint populations were significantly reduced (P<0.05), while Ly6clo monocyte numbers were unaffected. Further, flow cytometric analysis of blood and synovial macrophages identified a population of Ly6clo monocytes in the joint of C57Bl/6 mice which express endothelial cell surface marker CD105. 60% of Ly6clo monocytes in the joint were CD105+ compared to 14% and 16% of Ly6chi and Ly6cint respectively. Finally, transcriptional profiling of Ly6clo monocytes reveals upregulated genes in blood Ly6clo cells are enriched for processes such as monocyte activation and differentiation processes, compared to processes involved in cell migration and localization enriched in Ly6clo cells isolated from the joint.
These findings suggest a population of Ly6clo monocytes reside in the murine joint and have a distinct phenotype from blood Lyc6lo monocytes measured by cell surface markers and transcriptional profile. Combined with the finding that NR4A1-/- mice are susceptible to KBxN arthritis, this sub-population of Ly6clo monocytes is likely to have unique pro-inflammatory capabilities.
To cite this abstract in AMA style:Montgomery AB, Homan PJ, Winter DR, Perlman H. The Distinct Profile of Ly6clo Monocytes in the Murine Joint Compared with Those in Circulation Suggests a Unique Role in Inflammatory Arthritis [abstract]. Arthritis Rheumatol. 2018; 70 (suppl 9). https://acrabstracts.org/abstract/the-distinct-profile-of-ly6clo-monocytes-in-the-murine-joint-compared-with-those-in-circulation-suggests-a-unique-role-in-inflammatory-arthritis/. Accessed March 21, 2023.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-distinct-profile-of-ly6clo-monocytes-in-the-murine-joint-compared-with-those-in-circulation-suggests-a-unique-role-in-inflammatory-arthritis/