ABSTRACT: Human peripheral blood monocytes (Mo) consist of subsets distinguished by expression of CD16 (FCGRIII) and chemokine receptors. Classical CD16- Mo express CCR2 and migrate in response to CCL2, while a minor CD16+ Mo subset expresses CX3CR1 and migrates into tissues expressing CX3CL1. CD16+ Mo produce pro-inflammatory cytokines and are expanded in certain inflammatory conditions including HIV infection. To gain insight into the developmental relationship and functions of CD16+ and CD16- Mo, we examined transcriptional profiles of these Mo subsets in peripheral blood from healthy individuals. Of 16,328 expressed genes, 2,759 genes were differentially expressed and 228 and 250 were >2-fold upregulated and downregulated, respectively, in CD16+ compared to CD16- Mo. CD16+ Mo were distinguished by upregulation of dendritic cell (DC) (SIGLEC10, CD43, RARA) and macrophage (MF) (CSF1R/CD115, MafB, CD97, C3aR) markers together with transcripts relevant for DC-T cell interaction (CXCL16, ICAM-2, LFA-1), cell activation (LTB, TNFRSF8, LST1, IFITM1-3, HMOX1, SOD-1, WARS, MGLL), and negative regulation of the cell cycle (CDKN1C, MTSS1), whereas CD16- Mo were distinguished by upregulation of myeloid (CD14, MNDA, TREM1, CD1d, C1qR/CD93) and granulocyte markers (FPR1, GCSFR/CD114, S100A8-9/12). Differential gene expression in CD16+ and CD16- Mo was confirmed by quantitative real time RT-PCR (i.e., CD16, C3AR1, C1QR1, ICAM-2, CSF1R, CSF3R, CDKN1C, TNFRSF1, and LTB) and flow cytometry (i.e., CSF1R, CSF3R, C1QR1, C3AR1, CD1d, CD43, CXCL16, and CX3CR1). Furthermore, increased expression of RARA and KLF2 transcripts in CD16+ Mo coincided with absence of cutaneous lymphocyte associated antigen (CLA) expression, indicating potential imprinting for non-skin homing. These results suggest that CD16+ and CD16- Mo originate from a common myeloid precursor, with CD16+ Mo having a more MF- and DC-like transcription program suggesting a more advanced stage of differentiation. Distinct transcriptional programs, together with their recruitment into tissues via different mechanisms, also suggest that CD16+ and CD16- Mo give rise to functionally distinct DC and MF in vivo. Experiment Overall Design: Total Mo were isolated by negative selection using magnetic immunobeads (Monocyte Isolation Kit II, Miltenyi). CD16+ and CD16- Mo fractions were further isolated using CD16 magnetic immunobeads (Miltenyi). Total RNA from Mo pellets was isolated by Trizol extraction and purified using RNeasy columns (Qiagen). The quality of RNA was assessed by visualization of intact bands corresponding to 18S and 28S rRNA on formaldehyde agarose gels. Total RNA (10 µg) from matched CD16+ and CD16- Mo samples isolated from 4 different healthy donors was quality tested using an Agilent 2100 Bioanalyzer chip, reverse transcribed, and hybridized on the GeneChip Human Genome U133 Plus 2.0 Array (Affymetrix), which includes 54,000 probe sets on a single array (i.e., 47,000 transcripts and variants, including 38,500 well-characterized human genes). Primary data analysis performed using GeneSpring software (Biopolymer core facility, Harvard Medical School) generated Excel spreadsheets with relative gene expression values for the 4 matched CD16+ and CD16- Mo subsets.
