## 2 Materials and Methods  
**Mice.** BALB/c wildtype mice were obtained from the National Cancer Institute (Wilmington, MA) and Jackson labs (Bar Harbor, ME). Nr4a1-GFP reporter mice were originally described by [PERSON] et al. [20] and were backcrossed onto the BALB/c background for >12 generations. All mouse experiments were approved by the UCSF Institutional Animal Care and Use Committee, and animals received humane care in accordance with the criteria outlined in the Guide for the Care and Use of Laboratory Animals. Mice were euthanized by decapitation (pups < 7 days old) or carbon dioxide inhalation (pups \(\geq\) 7 days of age).  
**Creation of single-cell suspensions from fetal and neonatal livers.** The liver and bone marrow were isolated from euthanized mice. To create single-cell suspensions, livers were weighed upon extraction and washed in cold PBS over ice for 5 min. Using sterile fine surgical scissors, livers were cut into small pieces to facilitate mechanical dissociation in cold PBS (for pups at 3 days of life) and in 2.5 mg/mL Liberale (Roche, Indianapolis, IN, USA, 0540119001) homogenization buffer (for pups at 14 days of life). Once the liver was completely homogenized, the cell suspension was passed through a 100 \(\upmu\)m cell strainer to remove any undigested tissue or debris and to create SCS. Neonatal bone marrow was extracted by harvesting the sacral spine, pelvic bone, both femurs and tibas from each pup and washing them in cold PBS over ice for 5 min followed by crushing the bones using a pestle and mortar and washing the cells using cold PBS once the bones were completely crushed. Washed cells were then passed through a 100 \(\upmu\)m cell strainer to remove any undigested bone or debris and to create an SCS. Both the liver and BM SCS were then incubated in 1 mL of ACK Lysis buffer (Gibco, Waltham, MA, USA, A10492-01) over ice to remove red blood cells, followed by manual cell counting to determine cell count and viability. Cells were also stained using Ghost Live/Dead stain (Tonbo, San Diego, CA, USA, 13-0870-T100) to determine cell viability in analysis.  
**Flow cytometry.** Liver and bone marrow single-cell suspensions were stained using the following antibodies: Cd11c, clone N418 (Biolegend, San Diego, CA, USA, 117339); Ly6C, clone HK1.4 (Biolegend, 128035); MHCII, clone M5/114.15.2 (eBioscience, Waltham, MA, USA, 48-5321-82); Cd45, clone 30-F11 (eBioscience, 56-0451-82); Cd11b, clone M1/70 (eBioscience, 47-0112-82); Cd64, clone X54-5/7.1 (BD Biosciences, Franklin Lakes, NJ, USA, 741024); Ly6g, clone 1A8 (BD Biosciences, 560601); Fc block Cd16/Cd32, clone 2.4G2 (BD Biosciences, 553142); Lyeg, RB6-Sc5 (Tonbo, San Diego, CA, USA, 60-5931); Ghost(Tonbo, 13-0870-T100). Flow cytometric data were acquired on a BD LSRII Fortsessa X20 and analyzed using FlowJo (v10.8.1 Franklin Lakes, NJ, USA).  
**Postnatal model of perinatal inflammation.** Rhesus rotavirus (RRV) and Cercopithe-cus aethiops kidney epithelial (MA104) cells were obtained from Dr. [PERSON] (Stanford University, Palo Alto, CA, USA). The virus was grown and ittered in MA104 cells. To induce postnatal hepatic inflammation, P0 pups were injected intraperitoneallyally with \(1.5\times 10^{6}\) focus-forming units (ffu) 24 h after delivery. Controls were injected with PBS using the same technique.  
**Data analysis.** To compare the two groups, the unpaired t-test with [PERSON]'s correction, the non-parametric Mann-Whitney test, and the Chi-square test were used, respectively, for normally distributed variables, non-normally distributed variables, and proportions. A one-way ANOVA with [PERSON]'s multiple comparisons test was used to compare multiple groups. Myeloid populations after Ab-mediated depletion were quantified by dividing the number of live cells of interest by organ weight. Graphpad Prism 9.0 (San Diego, CA, USA) was used to generate graphs and perform statistical analysis.