Figure 5. Monocytes are poised to differentiate into GVHD macrophages.

(A) Comparison of PBMCs of healthy control, transplant patients without GVHD, and patients with GVHD. CD3^–CD4⁺HLA-DR⁺ monocyte and DC populations were divided into CD14⁺ classical monocytes and CD14^–CD16^– DCs, including CD123⁺CD11c^lo pDC, CD141⁺ cDC1, and CD1c⁺ cDC2. Representative examples of 10 experiments are shown. Frequencies of gated CD14⁺ monocytes and CD1c⁺ cDC2 are indicated as percentages of HLA-DR⁺ cells. (B) Ratio of CD14⁺ monocytes to CD1c⁺ cDC2 in blood of GVHD patients (n = 15), BMT controls (n = 16), and healthy controls (n = 15) analyzed by flow cytometry, as shown in A. Data are represented as mean + SEM. *P < 0.05; **P < 0.01, 1-way ANOVA and Tukey’s multiple comparison tests. (C) Genes differentially expressed between healthy control monocytes and GVHD classical monocytes (upregulated in red and downregulated in purple) at fold difference in log₂ gene expression of greater than 1.3 and P < 0.05. Cells sorted from n = 6 GVHD and n = 3 HC individuals. (D) Radial plot showing mean expression of chemokine genes in whole skin from patients with GVHD (red line; n = 10) and healthy controls (blue line; n = 6). Expression of the corresponding receptors by monocyte, T cell, or both is indicated. (E) Correlation between blood CD14⁺ monocyte frequency and CD11c⁺CD14⁺ content of GVHD dermis in paired blood and skin samples from 10 patients with GVHD. Statistical test by linear regression.