Background/Purpose: Rho GTPases, such as RhoA, are emerging as important regulators of lymphocyte biology owing to their ability to be rapidly activated downstream of a broad range of signals. Two of the major effectors of RhoA signaling are the Rho Kinases (ROCKs), ROCK1 and ROCK2, a pair of serine-threonine kinases that have been previously implicated in the control of cell adhesion, migration, proliferation/survival, and gene expression. Despite the fundamental reliance of T and B cells on these processes, the precise involvement of the ROCKs in lymphocyte biology is yet to be elucidated. Our laboratory previously identified a role for ROCK2 in the differentiation of T_H17 cells through the phosphorylation of IRF4. This ROCK2-pIRF4 pathway drives the production of key effector cytokines, such as IL-21, and is deregulated in several autoimmune models. While previous studies have focused on the role of ROCK2 in the T cell compartment, ROCK2 is expressed in other immune cell types, including B cells, leading us to hypothesize that ROCK2 may play a broad role in immunoregulation and T-B collaborations.

Methods: To assess the role of B-cell ROCK2 in T cell-dependent responses, WT mice or mice with B cell-specific deletion of ROCK2 were immunized with a T-dependent antigen and differentiation of germinal center (GC) B cells and plasmablasts/plasma cells (PB/PCs) was monitored by FACS. The molecular mechanisms employed by ROCK2 to promote B cell differentiation was further examined by FACS-sorting B cell populations from spleens of immunized mice followed by qPCR and immunoblot analyses. Total and antigen-specific antibody responses were assessed by ELISA.

Results: We found that ROCK2 is activated in GC B cells and in PB/PCs following immunization and that ROCK2 activity is also induced in vitro upon stimulation with T-cell derived signals such as aCD40 and IL-21. Mice with B cell-specific deletion of ROCK2 exhibited no abnormalities in their mature B cell compartments at baseline, yet showed marked decreases in total and antigen-specific antibody titers in response to immunization with a TD antigen. These decreased humoral responses corresponded with diminished germinal center formation and maintenance following antigen challenge. Residual germinal centers in ROCK2-deficient mice revealed skewed frequencies of GC subpopulations, reduced proliferation, and attenuated class switching to IgG1.

Conclusion: Our study demonstrates that ROCK2 is activated in B cells following immunization with a TD antigen and is required for optimal GC maintenance and function. These findings thus uncover a previously unknown B cell-intrinsic role for ROCK2 in promoting humoral responses and further support the notion that targeting ROCK2 activity may provide therapeutic benefit for the treatment of diseases marked by aberrant B cell responses.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-rho-kinase-family-member-rock2-promotes-germinal-center-responses-and-is-required-for-optimal-humoral-immunity/