Background/Purpose: Toll-like receptors (TLRs) dependent on Unc93b1 and cytosolic sensors dependent on STING detect microbial and endogenous nucleic acids to initiate inflammatory responses that resolve infection, but also contribute to autoimmune diseases. In the DNase II^-/- IFNaR^-/- (double knock out, DKO) mouse model, DNA accrual results in STING-dependent inflammatory arthritis as well as Unc93b1-dependent autoimmune manifestations, including ANA production, extramedullary hematopoiesis, and splenomegaly. While the role of hematopoietic cells in driving autoimmunity is well established, the contribution of stromal elements to disease pathogenesis is just beginning to be appreciated. Here we utilized bone marrow chimeras to determine the contribution of hematopoietic vs. radioresistant host cells to autoimmune manifestations in DKO mice.

Methods: Lethally irradiated Het (DNase II^+/- IFNaR^-/-) or DKO mice were reconstituted with Het or DKO stem cells to generate four experimental groups: Het (donor)→Het (recipient), DKO→DKO, Het→DKO and DKO→Het. Additionally, Unc93b1^-/- DNase II^-/- IFNaR^-/-triple KO (Unc93b1 TKO) mice were used to generate DKO→Unc93b1 TKO and Unc93b1 TKO→DKO chimeras. Complete hematopoietic repopulation by donor BM cells in all groups was verified by flow cytometry using appropriate markers. Inflammation was assessed by clinical scoring (scale of 1-12), histologic scoring in ankle joints (scale of 1-4), and by measuring matrix metalloproteinase 3 (MMP-3) protein levels in the sera. Splenomegaly, ANA production, and extramedullary hematopoiesis were evaluated as other indicators of disease.

Results: As expected, Het→Het chimeras showed no evidence of arthritis while DKO→DKO mice showed significant inflammation in distal joints. Remarkably, neither the DKO→Het nor Het→DKO mice developed any clinical or histologic signs of arthritis over a 10-month period. Serum MMP3, a surrogate marker for inflammation, reflected the arthritis scores and further confirmed absence of inflammation in the DKO→Het and Het→DKO chimeras. The massive splenomegaly and extramedullary hematopoiesis observed in DKO mice were absent in the Het→Het chimeras and present in DKO→DKO mice. Surprisingly however, the Het→DKO and DKO→Het mice failed to develop splenomegaly or extramedullary hematopoiesis. Furthermore, autoimmune manifestations dependent on Unc93b1 were present in the DKO→Unc93b1 TKO mice but absent in Unc93b1 TKO→DKO chimeras.

Conclusion: These data reveal that both hematopoietic and radioresistant host cells must be DNase II-deficient in order for STING-dependent inflammatory arthritis to develop. Additional features of autoimmunity in these mice known to depend on Unc93b1, and therefore on endosomal TLRs, also require DNase II deficiency in both donor and host compartments, but require functional TLRs only in hematopoietic cells. These findings point to a critical interplay between endosomal and cytosolic nucleic acid receptors in the development of systemic autoimmunity, and suggest that targeting both hematopoietic and non-hematopoietic cells may be advantageous in autoimmune settings.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/synergy-between-hematopoietic-and-radioresistant-stromal-cells-is-required-for-autoimmune-manifestations-of-dnase-ii-deficient-mice/