Background/Purpose: SLE is a disease that disproportionately affects females. The etiology of the sex bias in this disease is unclear. We previously showed that a functional knockout of estrogen receptor alpha (ERaKO) resulted in significantly reduced renal disease and increased survival in murine lupus. The mechanism of this effect, which requires estrogen, is not known.  Interestingly, an ERa-/- (null mutant) mouse is not similarly protected. We and others have demonstrated a role for ERa in dendritic cell (DC) development. Here we show that selective genetic disruption of ERa in DCs of lupus prone mice results in a survival difference, but only in females, who die prematurely compared with intact females.

Methods: Floxed-ERa and Cre-CD11c strains were backcrossed onto the NZM2410 lupus-prone background for 12 generations. Animals were validated by sorting CD11c+ DCs from Flt3L-cultured bone marrow; CrePos/Floxed-ERa mice had mRNA levels of ERa in DCs reduced by ~90%. Urine and blood were collected at select intervals and mice were sacrificed at 52 weeks, or earlier if they had high proteinuria or >10% weight loss. Spleen cells were isolated and flow cytometry was performed to determine number and subset of DC (cDCs: MHCII+/CD11c++/CD11b+; tolerogenic DCs: MHCII+/CD11c++/CD8a+; and pDCs: MHCII+/CD11c+/B220+/SiglecH+).

Results: n=12 CrePos/Floxed-ERa (DC-specific ERaKO) and n=12 CreNeg/Floxed-ERa animals were entered into the study.  There was no significant difference in survival between the 2 groups (males and females).  However, considered separately, survival of female lupus prone mice was significantly different. Median age at death was 30.0 weeks (± 1.807) n=6 for the CrePos and 40.4 weeks (± 3.891) n=7 for the CreNeg females (p<0.042). At 52 weeks: CrePos (DC-specific ERaKO) 0/6 were alive (0%) vs. CreNeg – 3/7 were alive (43%). Preliminary flow cytometry results revealed decreased percent of CD8a+ tolerogenic DCs in CrePos vs. CreNeg/FloxedERa, as well as increased percent of both CD11c++/CD11b+ cDCs and pDCs in CrePos vs. CreNeg/FloxedERa.

Conclusion: Selective deletion of ERa in DCs of lupus-prone mice results in reduced survival, but only in female animals. These mice had fewer tolerogenic DCs and increased numbers of both inflammatory cDCs and pDCs from spleen, which may partially explain the phenotype. This data joins a growing body of evidence that estrogen and ERa play critical roles in modulating immune cell development and function that impact autoimmune disease.