Cellular composition of SLE synovial fluid
Subsequently, we were interested in the cellular composition found in SF of SLE patients. SFMC were available from two SLE patients, one with as multiple timepoints as described above and another with cells from two timepoints. These samples were compared with SFMC from three SpA and two age and sex matched seronegative RA patients. All samples were investigated for T-cell phenotypes and when possible also for B cell, monocyte and dendritic cell subsets (Supplementary Table S4).
In SLE SF, lymphocytes consisted mainly of CD3+ T cells, with CD8+ cells being more common in SF than in PB (Fig. 2B, Supplementary Fig. 3A). B cells which were rare (<1%) displayed a memory phenotype, for one patient including age associated CD11c+ CD27+ B cells (Fig. 2B).
Examining the monocyte and dendritic cell (DC) subsets in SLE-SF, 64-67% of the HLA-DR+ cells expressed CD14 without expressing CD16, a sign for classical monocytes (Fig.2B, Supplementary Fig. S3C). Non-monocyte cells represented ~30% of HLA-DR+ cells in SF, and were mostly classical DC (CD11c+, cDC), in patient one mainly cDC1 while the other exhibited equal proportions of cDC1 and cDC2.The frequency of plasmacytoid DC varied between patients from 7-26% (Fig. 2B, Supplementary Fig. S3C).