Abstract Body: Impaired uterine vascular remodeling is a hallmark of preeclampsia, a hypertensive disorder of pregnancy with global impact on maternal-fetal health. Obesity is a major risk factor for preeclampsia and may play a role in uteroplacental vascular dysfunction. However, the pathology behind this is not fully understood. The Blood Pressure High 5 (BPH/5) mouse is an established model of obesity and superimposed preeclampsia. Pregnant BPH/5 mice spontaneously develop poor uteroplacental vascular remodeling, placental dysfunction, hypertension, and fetal compromise. BPH/5 mice also have significantly more perivascular adipose tissue (PVAT) around uterine arteries (utPVAT). While utPVAT is relatively uncharacterized, other PVATs modulate vascular function and have rich immune cell populations, which are altered in obesity. Thus, this study investigated the hypothesis that utPVAT immune profiles differ between BPH/5 and normotensive BPN/3 mice pre-pregnancy and during late gestation. To address this hypothesis, adult (8-12 weeks) virgin and strain-matched timed-mated BPN/3 and BPH/5 females were used. Day of copulation was defined as embryonic day (e) 0.5. Flow cytometry was performed on the stromal vascular fractions of utPVAT from non-pregnant (NP) and late-gestation (e18.5) BPN/3 and BPH/5 females (n=6/group). Notably, both prior to pregnancy and in late gestation the utPVAT environment in BPN/3 mice is eosinophil-rich, whereas BPH/5 utPVAT is macrophage-rich. There were a number of strain differences in utPVAT immune cell composition of NP females in which the most notable differences were a decreased percentage of eosinophils (NP BPN/3: 28.9 ± 1.7% vs. NP BPH/5: 15.8 ± 1.7%, p<0.01) and an increased percentage of macrophages (NP BPN/3: 8.7 ± 0.4% vs. NP BPH/5: 34.8 ± 2.5%, p<0.0001). Pregnancy caused changes in utPVAT immune cell composition in both strains. Specifically, pregnancy decreased the percentage of utPVAT eosinophils in e18.5 BPH/5 (e18.5 BPH/5: 6.7 ± 1.3 vs. NP BPH/5: 15.8 ± 1.7%, p<0.05), but not BPN/3, mice. Pregnancy also decreased the percentage of utPVAT dendritic cells and NK cells in both strains (p<0.05). Therefore, disrupted utPVAT immune profile predates pregnancy in the preeclamptic-like BPH/5 mouse. Future studies will focus on underlying mechanisms, translatability, and therapeutic potential of these findings in the context of preeclampsia.