Using scRNA-seq, Rao et al. classified human HF macrophages into three principal subsets: CCR2-HLA-DRhi, CCR2+HLA-DRhi, and TREM2+ macrophages, which correspond to murine Ccr2-MHCIIhi, Ccr2+MHCIIhi, and Trem2+ subsets, respectively 122. The gene discussed is CCR2; the disease is hydrops fetalis.