Background/Purpose: Follicular helper T (T_FH) cells promote humoral responses and serve as a limiting factor for the selection of high affinity germinal center B cells. T_FH cell numbers need to be tightly regulated, and T_FH cell expansion has been associated with autoimmune diseases including SLE. Rho-associated kinases (ROCKs), ROCK1 and ROCK2, are major downstream effectors of the small GTPase RhoA. The ROCKs regulate both gene expression and cytoskeletal reorganization. Increased ROCK activation has been observed in autoimmune disease both in mice and humans, and ROCK inhibition ameliorates autoimmunity in murine models. However, the underlying molecular and cellular mechanisms by which the ROCKs affect autoimmune disease are currently unknown. Here we investigated the role of ROCK2 in T_FH cell expansion under physiological conditions and in autoimmunity by employing mice lacking DEF6 and SWAP-70, which exhibit aberrant ROCK activation, accumulation of T_FH cells, and spontaneously develop a lupus-like disease.

Methods: Mice lacking ROCK2 in T cells were generated by crossing CD4^cre mice with ROCK2^flox/flox mice. The T_FH cell compartment was assessed in CD4^creROCK2^flox/flox mice by immunizing with a T-dependent antigen. To evaluate the effect of T-cell ROCK2 on autoimmune disease CD4^creROCK2^flox/flox mice were crossed with Def6^trap/trapSwap-70^-/- mice (DKO mice), which develop a lupus-like disease primarily in females. Flow cytometry analysis and ELISAs were used to assess T_FH cell expansion and autoantibody production.

Results: The absence of ROCK2 in T cells did not lead to any abnormality in the frequencies or activation state of the T cell compartment at baseline. Lack of T cell ROCK2, however, resulted in a significant decrease in T_FH cell formation upon immunization with a T-dependent antigen. This was associated with a reduction in germinal center B cell and plasma cell formation suggesting that T-cell ROCK2 is essential for T-dependent immune responses. To evaluate the contribution of T-cell ROCK2 to T_FH cell formation in autoimmunity, we analyzed CD4^creROCK2^flox/flox Def6^trap/trapSwap-70^-/- mice (ROCK2ΔT DKO) mice. Upon deletion of T cell ROCK2, the spontaneous increase in T_FH cells observed in DKO mice was significantly reduced. This was associated with decreased GC B cells, plasma cell numbers, and diminished anti-dsDNA autoantibody levels.

Conclusion: Our current study indicates that ROCK2 regulates T_FH cells both during T-dependent immune responses as well as in autoimmune settings further supporting a role for ROCK inhibition as a potential treatment for SLE and other autoimmune diseases that exhibit dysregulation in T_FH cells.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/regulation-of-follicular-helper-t-tfh-cells-by-rock2-rho-associated-coiled-coil-containing-protein-kinase-2/