Highlights d Granzyme B + CD8 + T cells accumulate in the brain after traumatic brain injury (TBI) d Brain CD8 + T cells contribute to chronic motor deficits and myelin pathology d Deficiency/depletion of CD8 + T cells promotes neurological recovery following TBI d B cells and autoreactive antibodies appear to play a regulatory role in TBI

Rho-kinase (ROCK) inhibition, broadly utilised in cardiovascular disease, may protect the blood-brain barrier (BBB) during thrombolysis from rt-PA-induced damage. While the use of nonselective ROCK inhibitors like fasudil together with rt-PA may be hindered by possible hypotensive side-effects and inadequate capacity to block detrimental rt-PA activity in brain endothelial cells (BECs), selective ROCK-2 inhibition may overcome these limitations. Here, we examined ROCK-2 expression in major brain cells and compared the ability of fasudil and KD025, a selective ROCK-2 inhibitor, to attenuate rt-PA-induced BBB impairment in an in vitro human model. ROCK-2 was highly expressed relative to ROCK-1 in all human and mouse brain cell types and particularly enriched in rodent brain endothelial cells and astrocytes compared to neurons. KD025 was more potent than fasudil in attenuation of rt-PA- and plasminogen-induced BBB permeation under normoxia, but especially under stroke-like conditions. Importantly, only KD025, but not fasudil, was able to block rt-PA-dependent permeability increases, morphology changes and tight junction degradation in isolated BECs. Selective ROCK-2 inhibition further diminished rt-PA-triggered myosin phosphorylation, shape alterations and matrix metalloprotease activation in astrocytes. These findings highlight ROCK-2 as the key isoform driving BBB impairment and brain endothelial damage by rt-PA and the potential of KD025 to optimally protect the BBB during thrombolysis.

Background Traumatic brain injury (TBI) is known to promote immunosuppression, making patients more susceptible to infection, yet potentially exerting protective effects by inhibiting central nervous system (CNS) reactivity. Plasmin, the effector protease of the fibrinolytic system, is now recognized for its involvement in modulating immune function. Objective To evaluate the effects of plasmin and tranexamic acid (TXA) on the immune response in wild‐type and plasminogen‐deficient (plg−/−) mice subjected to TBI. Methods Leukocyte subsets in lymph nodes and the brain in mice post TBI were evaluated by flow cytometry and in blood with a hemocytometer. Immune responsiveness to CNS antigens was determined by Enzyme‐linked Immunosorbent Spot (ELISpot) assay.  Fibrinolysis was determined by thromboelastography and measuring D‐dimer and plasmin‐antiplasmin complex levels. Results Plg−/− mice, but not plg+/+ mice displayed increases in both the number and activation of various antigen‐presenting cells and T cells in the cLN 1 week post TBI. Wild‐type mice treated with TXA also displayed increased cellularity of the cLN 1 week post TBI together with increases in innate and adaptive immune cells. These changes occurred despite the absence of systemic hyperfibrinolysis or coagulopathy in this model of TBI. Importantly, neither plg deficiency nor TXA treatment enhanced the autoreactivity within the CNS. Conclusion In the absence of systemic hyperfibrinolysis, plasmin deficiency or blockade with TXA increases migration and proliferation of conventional dendritic cells (cDCs) and various antigen‐presenting cells and T cells in the draining cervical lymph node (cLN) post TBI. Tranexamic acid might also be clinically beneficial in modulating the inflammatory and immune response after TBI, but without promoting CNS autoreactivity.

Background Tranexamic acid (TXA) is an antifibrinolytic agent frequently used in elective surgery to reduce blood loss. We recently found it also acts as a potent immune-modulator in patients undergoing cardiac surgery. Methods Patients undergoing lower limb surgery were enrolled into the “Tranexamic Acid in Lower Limb Arthroplasty” (TALLAS) pilot study. The cellular immune response was characterised longitudinally pre- and post-operatively using full blood examination (FBE) and comprehensive immune cell phenotyping by flowcytometry. Red blood cells and platelets were determined in the FBE and levels of T cell cytokines and the plasmin-antiplasmin complex determined using ELISA. Results TXA administration increased the proportion of circulating CD141+ conventional dendritic cells (cDC) on post-operative day (POD) 3. It also reduced the expression of CD83 and TNFR2 on classical monocytes and levels of circulating IL-10 at the end of surgery (EOS) time point, whilst increasing the expression of CCR4 on natural killer (NK) cells at EOS, and reducing TNFR2 on POD-3 on NK cells. Red blood cells and platelets were decreased to a lower extent at POD-1 in the TXA group, representing reduced blood loss. Conclusion In this investigation we have extended our examination on the immunomodulatory effects of TXA in surgery by also characterising the end of surgery time point and including B cells and neutrophils in our immune analysis, elucidating new immunophenotypic changes in phagocytes as well as NK cells. This study enhances our understanding of TXA-mediated effects on the haemostatic and immune response in surgery, validating changes in important functional immune cell subsets in orthopaedic patients.