Implications of the Regulation of Endothelial Glycocalyx Breakdown and Reconstitution in Severe Burn Injury.

INTRODUCTION: Effective initial fluid resuscitation is the cornerstone intervention in the setting of severe burn injury. Critically, few major advances in burn resuscitation have been made since the 1970s, and since that time there has been only modest improvement in overall morbidity and mortality. Recently, investigations regarding the dynamic changes of vascular endothelium, and more specifically the vascular endothelial glycocalyx, in the setting of severe burn injury and resuscitation have offered insight into the possibility of more tightly controlling fluid shifts and understanding the consequences thereof during this critical period. METHODS: We conducted a literature search of the PubMed database using the terms "burn", and "glycocalyx" limited to studies published in the English language over the past 10 y. A total of 31 articles were initially identified. Abstracts and full text were manually reviewed to identify suitable articles. Of the identified articles, 10 were deemed relevant and included within this review, along with additional articles necessary to provide background on glycocalyx structure and function as well as principles of burn injury management. RESULTS: Glycocalyx shedding is a process known to occur early in the setting of severe burn injury and resuscitation. The degree of shedding tends to increase with age and severity of injury. Though the role and regulation of this shedding is incompletely understood, it has direct consequences on vascular unction and permeability and likely coagulation as well. CONCLUSIONS: Here in this research review, we examine what is known regarding the dynamic breakdown and reconstitution of the glycocalyx during burn injury and how it may be impacted by fluid resuscitation strategies. We further explore the need to more completely understand this mechanism and the consequences of its manipulation.

Assessment of Neurological Impairment and Recovery Using Statistical Models of Neurologically Healthy Behavior.

While many areas of medicine have benefited from the development of objective assessment tools and biomarkers, there have been comparatively few improvements in techniques used to assess brain function and dysfunction. Brain functions such as perception, cognition, and motor control are commonly measured using criteria-based, ordinal scales which can be coarse, have floor/ceiling effects, and often lack the precision to detect change. There is growing recognition that kinematic and kinetic-based measures are needed to quantify impairments following neurological injury such as stroke, in particular for clinical research and clinical trials. This paper will first consider the challenges with using criteria-based ordinal scales to quantify impairment and recovery. We then describe how kinematic-based measures can overcome many of these challenges and highlight a statistical approach to quantify kinematic measures of behavior based on performance of neurologically healthy individuals. We illustrate this approach with a visually-guided reaching task to highlight measures of impairment for individuals following stroke. Finally, there has been considerable controversy about the calculation of motor recovery following stroke. Here, we highlight how our statistical-based approach can provide an effective estimate of impairment and recovery.

Emergency department visit patterns in the recently discharged, violently injured patient: Retrospective cohort review.

BACKGROUND: Analysis of the costs associated with emergency department (ED) visits after discharge for violent injury could highlight subgroups for the development of cost-effective interventions to support healing and prevent treatment failures in violently injured patients. METHODS: A retrospective cohort review was conducted of all patients with return ED visits within 90 days of discharge after treatment for a violent injury occurring between July 1, 2016, and June 30, 2018. Hospital costs were calculated for each incidence and analyzed against demographic and injury type variables to identify trends. RESULTS: 218 return ED visits were identified. Hospital costs showed a high frequency of low-cost visits. For more complex visits, distinct cost patterns were observed for Black and LatinX males compared to White males as a function of age. CONCLUSIONS: Analysis of hospital cost per visit identified trends among different subgroups. Underlying etiologies presumably vary between groups, but hypothesis-driven further investigation and needs assessment is required. Understanding the driving forces behind these cost trends may aid in developing effective interventions.

The hidden mortality of pediatric firearm violence.

INTRODUCTION: Firearms and motor vehicle collisions (MVC) are leading causes of mortality in children. We hypothesized that firearm injuries would have a higher mortality than MVCs in children and a higher level of resource utilization METHODS: Trauma patients <18 years old at a Level 1 pediatric trauma center sustaining gunshot wounds (GSW) or MVCs 2009-2019 were included. The primary outcome was mortality. The secondary outcome was immediate surgery. The California Department of Public Health's Overall Injury Surveillance tool was queried for patients <18 with GSW or MVC 2006-2015 to compare statewide case fatality rates (CFRs), and analyze proportions of GSWs by intent: assault, self-inflicted, and unintentional. RESULTS: Of 13,840 pediatric trauma patients at our institution, 295 GSWs (2.1%) and 4467 MVCs (32.3%) were included. Mortality was higher for GSWs (7.5% vs. 0.8%, p<0.0001). GSW patients were more likely to require immediate surgery (34.4% vs. 11.2%, p<0.0001). On multivariable analysis, GSW patients were 7.8-times more likely to die than MVC patients (OR 7.83, 95% CI 3.68-16.66, p<0.0001), adjusted for age, sex, and injury severity. Statewide, there were 10,790 pediatric GSWs with 1586 deaths (CFR 14.7%) vs. 710 deaths in 261,363 children in MVCs (CFR 0.3%, p<0.0001). The GSW CFR rose (13.4% to 16.5%, p = 0.05) while the MVC CFR decreased (0.5% to 0.2%, p<0.0001) in 2015 vs. 2006. CONCLUSION: Firearm violence in pediatric patients is significantly more lethal than MVCs and is resource intensive. The case fatality rate for pediatric firearm violence is rising. Resources must be directed at preventing pediatric firearm injuries. LEVEL OF EVIDENCE: Prognosis study, Level II.

Viscoelastic Coagulation Monitor (VCMVet) Reference Intervals and Sex Differences in Mature Adult Mice.

INTRODUCTION: Viscoelastic coagulation tests are useful to assess coagulation status in the clinical setting and to aid in understanding underlying pathophysiological mechanisms that affect coagulation status. Such tests also are useful for coagulation research. Because mouse models are widely used to study molecular mechanisms in fine detail, a simple viscoelastic coagulation test requiring small blood volumes would be convenient for such studies in mice. METHODS: We tested viscoelastic coagulation properties of normal healthy adult mice using a novel veterinary clinical point-of-care device, Viscoelastic Coagulation Monitor (VCM Vet™; Entegrion Corp.). Fresh whole blood was collected from 63 healthy mature adult C57 black 6N mice, with ultimately 54 mice, equal numbers of male and females, used to determine reference intervals (RIs) for VCM test parameters. RESULTS: RIs were determined for equal numbers of male and female mice: clot time: 43.0-353.0 s; clot formation time: 49.4-137.6 s; alpha angle: 54.4-62.2°; A10: 25.0-49.6 VCM units; A20: 31.0-56.5 VCM units; maximum clot firmness: 37.6-62.8 VCM units; Lysis Index 30 (Li30): 99.8-100.0%; and Li45: 99.7-100.0%. Significant differences were found between male and female subgroups, where females had higher mean A10 and A20 and median MCF values, indicating greater clot firmness in female versus male mice. CONCLUSION: VCM Vet is a feasible viscoelastic coagulation test device for studies with mature adult mice, including studying inherent sex differences in coagulation parameters. Inherent differences in coagulability of male and female mice warrant further investigation to determine if such differences underlie greater coagulopathic, hemorrhagic, or thromboembolic risk during trauma or other pathophysiologic conditions.

P-selectin antibody treatment after blunt thoracic trauma prevents early pulmonary arterial thrombosis without changes in viscoelastic measurements of coagulation.

INTRODUCTION: Previously, in a murine model of blunt thoracic trauma, we provided evidence of primary pulmonary thrombosis associated with increased expression of the cell adhesion molecule, P-selectin. In this study, mice are treated with P-selectin blocking antibody after injury to investigate the clinical viability of this antibody for the prevention of pulmonary thrombosis. In addition, viscoelastic testing is performed to investigate if P-selectin inhibition has a detrimental impact on normal hemostasis. METHODS: A murine model of thoracic trauma was used. Mice were divided into sham control and experimental injury groups. Thirty minutes after trauma, mice were treated with the following: P-selectin blocking antibody, isotype control antibody, low-dose heparin, high-dose heparin, or normal saline. At 90 minutes, whole blood was collected for characterization of coagulation by viscoelastic coagulation monitor (VCM Vet; Entegrion, Durham, NC). Mean clotting time, clot formation time, clot kinetics (α angle), and maximum clot firmness were compared between each treatment group. RESULTS: Mice that received P-selectin antibody 30 minutes after blunt thoracic trauma had four- to fivefold less (p < 0.001) arterial fibrin accumulation than those that received the isotype control. In both sham and trauma groups, compared with vehicle (normal saline) alone, no statistical difference was noted in any coagulation parameters after injection with P-selectin antibody, isotype control, or low-dose heparin. In addition, blinded histopathological evaluation yielded no difference in hemorrhage scores between injured mice treated with P-selectin blocking antibody and those treated with isotype antibody control. CONCLUSION: This study supports the clinical use of P-selectin blocking antibody for the prevention of pulmonary thrombosis by confirming its efficacy when given after a blunt thoracic trauma. In addition, we demonstrated that the administration of P-selectin antibody does not adversely affect systemic coagulation as measured by viscoelastic testing, suggesting that P-selectin antibody can be safely given during the acute posttraumatic period.

High Versus Low Volume Fluid Resuscitation Strategies in a Porcine Model (Sus scrofa) of Combined Thermal and Traumatic Brain Injury.

BACKGROUND: Combined burn and traumatic brain injury (TBI) treatment priorities may not align due to opposing fluid resuscitation paradigms used in treating burns and TBI. We developed a porcine model of combined thermal injury/TBI and compared an "aggressive" fluid resuscitation strategy using the Parkland formula and a "restrictive" resuscitation strategy using the modified Brooke formula. METHODS: Twenty-eight swine were deeply anesthetized and received a 40% total body surface area full-thickness burn injury and TBI. Swine were then randomized to receive restrictive or aggressive resuscitation for 8 h after which time animals were euthanized and necropsy was performed. Volume of brain injury was assessed after analyzing segmental slices of brain tissue. RESULTS: There were no differences between the restrictive and aggressive resuscitation groups in blood pressure, heart rate, central venous pressure, intra-cranial pressure (ICP), or serum lactate levels after 8 h of resuscitation. Urine output was higher in the aggressive resuscitation group. The restrictive group had a significantly higher serum blood urea nitrogen (BUN) compared with baseline and compared with the aggressive group. There was no significant difference in size of brain injury between groups. CONCLUSIONS: Both restrictive and aggressive resuscitation demonstrated adequate resuscitation at 8 h postinjury. Increased serum BUN in the restrictive group may be an indicator of early acute kidney injury, despite adequate urine output. Resuscitation strategy did not appear to affect ICP or the size of brain injury.

Donor Characteristics, Recipient Outcomes, and Histologic Findings of Kidney Allografts With Diffuse Donor-derived Glomerular Fibrin Thrombi.

BACKGROUND: Limited data are available on whether donor kidneys with diffuse glomerular fibrin thrombi (GFT) are safe to use. In this study, the clinicopathologic characteristics of allografts with diffuse donor-derived GFT were examined. METHODS: All deceased donor kidney transplant implantation biopsies from our institution between July 2011 and February 2018 with diffuse GFT were included. A control group for comparison consisted of all cases with implantation biopsies obtained during the study period without diffuse GFT. Clinical data were extracted from electronic medical records for all study patients, including donor information. RESULTS: Twenty-four recipients received kidneys with diffuse GFT from 16 deceased donors. All donors died from severe head trauma. On average, 79% of glomeruli contained fibrin thrombi. Nineteen cases had subsequent biopsy; all revealed resolution of GFT. Compared with the control group, kidneys with diffuse GFT had longer cold ischemia time (34 versus 27 h), were more frequently pumped using machine perfusion (100% versus 81%), and recipients experienced a higher frequency of delayed graft function (58% versus 27%). Only 2 grafts with diffuse GFT failed within the first year. Overall graft survival was similar between the diffuse GFT group and control group. CONCLUSIONS: Deceased donor kidneys with diffuse GFT appear to be safe to use given that nearly 92% of recipients in this cohort who received such allografts experienced good clinical outcomes. Histologically, GFT demonstrated rapid resolution following transplantation. Interestingly, diffuse GFT only occurred in donors who suffered severe head trauma in this cohort, which may be a predisposing factor.

P-Selectin Is Critical for De Novo Pulmonary Arterial Thrombosis Following Blunt Thoracic Trauma.

BACKGROUND: Thromboembolic events within the pulmonary arterial vasculature are a troublesome complication of severe blunt thoracic trauma. Mechanisms underlying these events are currently in question as pulmonary thromboembolic events in this particular trauma population tend to be diagnosed more rapidly, more frequently and without an associated systemic thrombosis. This study investigates the role of P-selectin in thrombus formation through the use of in vivo blocking antibodies. We hypothesize that P-selectin plays a pivotal role in de novo pulmonary arterial thrombosis following blunt thoracic trauma. METHODS: A murine weight-drop model of lateral blunt thoracic trauma was used. Wild-type mice in the experimental group were given blocking antibodies against P-selectin prior to the trauma. All mice were euthanized at 24 hours for evaluation with hematoxylin-eosin staining or immunofluorescent staining for fibrin and P-selectin. RESULTS: Injured mice that did not receive the P-selectin antibody showed a robust fourfold to fivefold increase in fibrin accumulation in both coup and contrecoup tissues (fluorescence per um of arterial wall) compared to uninjured sham mice. In contrast, mice pretreated with P-selectin blocking antibody showed no significant increase in fibrin accumulation on either side of the lungs after blunt thoracic trauma. No difference in mean fibrin deposition was found between sham controls that received the P-selectin-blocking antibody and those that received an isotype control antibody. CONCLUSION: P-selectin expression increases at the pulmonary arterial luminal surface following blunt thoracic trauma. In addition, P-selectin-blocking in vivo prevents pulmonary arterial fibrin accumulation after blunt thoracic trauma, confirming that P-selectin is necessary for de novo pulmonary arterial thrombosis after traumatic injury.

Nonocclusive mesenteric ischemia in patients with methamphetamine use.

BACKGROUND: Data suggest that methamphetamine may increase the risk of nonocclusive mesenteric ischemia (NOMI). We describe patterns of presentation and outcomes of patients with methamphetamine use who present with NOMI to a single institution. METHODS: This is an observational study of patients from January 2015 to September 2017 with methamphetamine use who presented with NOMI at an academic medical center in Northern California. We summarize patient comorbidities, clinical presentation, operative findings, pathologic findings, hospital course, and survival. RESULTS: Ten patients with methamphetamine use and severe NOMI were identified. One patient was readmitted with a perforated duodenal ulcer, for a total of 11 encounters. Most presented with acute (n = 3) or acute-on-chronic (n = 4) abdominal pain. Distribution of ischemia ranged from perforated duodenal ulcer (n = 3), ischemia of the distal ileum (n = 1), ischemia of entire small bowel (n = 2), and patchy necrosis of entire small bowel and colon (n = 5). Six patients died, three within 1 week of admission and three between 3 months and 8 months. CONCLUSION: Methamphetamine use may be associated with significant microvascular compromise, increasing the risk of mesenteric ischemia. Providers in areas with high prevalence of methamphetamine use should have a high index of suspicion for intestinal ischemia in this patient population. Patients with methamphetamine use admitted for trauma or other pathology may be at particular risk of ischemia and septic shock, especially in the setting of dehydration. Use of vasoconstrictors in this patient population may also exacerbate intestinal ischemia. LEVEL OF EVIDENCE: Therapeutic Case series study, level V.

Pulmonary Arterial Thrombosis in a Murine Model of Blunt Thoracic Trauma.

Pulmonary thromboembolic events cause significant morbidity and mortality after severe trauma. Clinically, these lesions are believed to be emboli arising secondary to deep venous thrombosis (DVT) in the lower extremities. Recently, this notion has been challenged by clinical studies, showing that pulmonary clots arise after trauma in the absence of DVT. This suggests that pulmonary blood clots arise in situ via de novo thrombosis. In the present study, we characterize a murine weight-drop model of lateral blunt thoracic trauma. Our model demonstrates severe unilateral lung contusion injury with low (10%) mortality in the absence of extrapulmonary injury, after impact with a 50-g weight dropped from 45 cm height (657 J/m). At 24 h after injury, immunofluorescence and histological evidence revealed early pulmonary arterial thrombosis in the form of eccentric accumulation of fibrin and CD41 positive eosinophilic proteinaceous material, on both coup and contrecoup lung lobes of injured mice, indicating early thrombotic events both within and outside of the area of primary lung injury. Our model is ideal in that lateral impact enables greater impact energy to be applied to achieve significant lung contusion without significant mortality or extrapulmonary injury, and the model has additional translational value in creating thrombosis analogous to pulmonary embolism observed clinically after blunt thoracic trauma. To our knowledge, this is the first demonstration of de novo pulmonary thrombosis in a clinically translational model of blunt thoracic trauma, and supports challenges to current assumptions about the origin of pulmonary blood clots in the wake of severe traumatic injury.

Pelvic angioembolization in trauma - Indications and outcomes.

INTRODUCTION: Pelvic stabilization with angioembolization (AE) is steadily supplanting operative management for the treatment of pelvic hemorrhage in trauma. We aimed to provide a brief review of the indications, effectiveness and complications associated with AE for pelvic injuries. METHODS: We conducted a literature search using the terms "trauma," "angioembolization," and "pelvis" limited to studies published in the English language. Abstracts and full text were manually reviewed to identify suitable articles. RESULTS: The current brief review is based on content from articles published in the last 10 years related to pelvic AE for retroperitoneal hemorrhage after trauma. DISCUSSION: Pelvic injuries often require complex management because the high energy transfer causes concomitant injuries. Outcomes for hemodynamically unstable patients may be better with AE than with operative management. CONCLUSION: Pelvic AE is the most effective intervention for management of hemorrhage associated with pelvic fracture in both hemodynamically stable and unstable patients. It can be used as the primary definitive intervention or in conjunction with operative management in the setting of concomitant intra-abdominal injury.

Angioembolization for solid organ injury: A brief review.

INTRODUCTION: Non-operative management is the standard of care for blunt solid organ injuries in stable patients. Angioembolization is an important technique that improves success rates of non-operative management. We aimed to provide a brief review of the indications, effectiveness and complications associated with angioembolization for solid organ injuries. METHODS: We conducted a literature search of the PubMed database using the terms "trauma", "angioembolization", and "solid organ embolization" limited to studies published in the English language. Abstracts and full text were manually reviewed to identify suitable articles. RESULTS: The current brief review is based on content from the more recently published articles related to angioembolization for solid organ injuries after trauma. DISCUSSION: Angioembolization is appropriate for hemodynamically stable patients with contrast extravasation on CT scan or high-grade injury to a solid organ. Non-operative management success rates have improved with the adoption of angioembolization. The complications associated with angioembolization are acceptable in the context of avoiding a laparotomy, and are often related to the severity of the injury. CONCLUSION: Angioembolization is a natural extension of the move towards non-operative management for solid organ injuries. Randomized controlled trials are required to fully characterize the indications and efficacy of its use.

Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss.

Weight loss is accompanied by several metabolic adaptations that work together to promote rapid, efficient regain. We employed a rodent model of regain to examine the effects of a regular bout of treadmill exercise on these adaptations. Obesity was induced in obesity-prone rats with 16 wk of high-fat feeding and limited physical activity. Obese rats were then weight reduced (approximately 14% of body wt) with a calorie-restricted, low-fat diet and maintained at that reduced weight for 8 wk by providing limited provisions of the diet with (EX) or without (SED) a daily bout of treadmill exercise (15 m/min, 30 min/day, 6 days/wk). Weight regain, energy balance, fuel utilization, adipocyte cellularity, and humoral signals of adiposity were monitored during eight subsequent weeks of ad libitum feeding while the rats maintained their respective regimens of physical activity. Regular exercise decreased the rate of regain early in relapse and lowered the defended body weight. During weight maintenance, regular exercise reduced the biological drive to eat so that it came closer to matching the suppressed level of energy expenditure. The diurnal extremes in fuel preference observed in weight-reduced rats were blunted, since exercise promoted the oxidation of fat during periods of feeding (dark cycle) and promoted the oxidation of carbohydrate (CHO) later in the day during periods of deprivation (light cycle) . At the end of relapse, exercise reestablished the homeostatic steady state between intake and expenditure to defend a lower body weight. Compared with SED rats, relapsed EX rats exhibited a reduced turnover of energy, a lower 24-h oxidation of CHO, fewer adipocytes in abdominal fat pads, and peripheral signals that overestimated their adiposity. These observations indicate that regimented exercise altered several metabolic adaptations to weight reduction in a manner that would coordinately attenuate the propensity to regain lost weight.

Homeostatic proliferation plus regulatory T-cell depletion promotes potent rejection of B16 melanoma.

PURPOSE: To investigate the antitumor efficacy of T-cell anergy reversal through homeostatic proliferation and regulatory T-cell (Treg) depletion in a clinically relevant murine adoptive immunotherapy model. EXPERIMENTAL DESIGN: B16 melanoma cells were engineered to express the model SIYRYYGL (SIY) antigen to enable immune monitoring. Tumor-specific T cells expanded in tumor-challenged wild-type hosts but became hyporesponsive. To examine whether lymphopenia-induced homeostatic proliferation could reverse tumor-induced T-cell anergy, total splenic T cells were transferred into lymphopenic RAG2-/- mice or control P14/RAG2-/- mice. Tumor growth was measured, and SIY-specific immune responses were monitored using ELISPOT and SIY/K(b) tetramers. To determine whether Treg depletion could synergize with homeostatic proliferation, RAG2-/- mice received total or CD25-depleted T cells, followed or preceded by B16.SIY challenge. This approach was further investigated in wild-type mice lymphodepleted with sublethal total body irradiation. RESULTS: Adoptive transfer of total splenic T cells into RAG2-/- mice moderately affected the growth rate of B16.SIY. As Treg expansion occurred in tumor-bearing mice, CD25+ T cells were depleted from total T cells before adoptive transfer. Interestingly, transfer of CD25-depleted T cells into RAG2-/- mice resulted in potent rejection of B16 melanoma in both prophylactic and short-term preimplanted tumor settings and was associated with maintained T-cell effector function. Using a clinically applicable approach, wild-type mice were lymphodepleted using sublethal total body irradiation, which similarly supported tumor rejection upon transfer of CD25-depleted T cells. CONCLUSIONS: Our results indicate that combined CD25 depletion and homeostatic proliferation support a potent antitumor immune response--an approach with potential for clinical translation.

A planar 3DOF robotic exoskeleton for rehabilitation and assessment.

A new robotic exoskeleton for the upper-limb has been designed and constructed. Its primary purpose is to act as a proof-of-concept prototype for a more sophisticated rehabilitation and assessment device that is currently in development. Simultaneously, it is intended to extend the capabilities of an existing planar exoskeleton device. The robot operates in the horizontal plane and provides independent control of a user's shoulder, elbow and wrist joints using a cable-driven actuation system. The novel component of the design is a curved track and carriage which allows the mechanism that drives the shoulder joint to be located away from the user, underneath their arm. This paper describes the design of the robot, and provides an initial indication of its performance.

Homeostatic proliferation as an isolated variable reverses CD8+ T cell anergy and promotes tumor rejection.

Although recent work has suggested that lymphopenia-induced homeostatic proliferation may improve T cell-mediated tumor rejection, there is little direct evidence isolating homeostatic proliferation as an experimental variable, and the mechanism by which improved antitumor immunity occurs via homeostatic proliferation is poorly understood. An adoptive transfer model was developed in which tumor-specific 2C/RAG2(-/-) TCR transgenic CD8+ T cells were introduced either into the lymphopenic environment of RAG2(-/-) mice or into P14/RAG2(-/-) mice containing an irrelevant CD8+ TCR transgenic population. RAG2(-/-), but not P14/RAG2(-/-) recipients supported homeostatic proliferation of transferred T cells as well as tumor rejection. Despite absence of tumor rejection in P14/RAG2(-/-) recipients, 2C cells did become activated, as reflected by CFSE dilution and CD44 up-regulation. However, these cells showed poor IFN-gamma and IL-2 production upon restimulation, consistent with T cell anergy and similar to the hyporesponsiveness induced by administration of soluble peptide Ag. To determine whether homeostatic proliferation could uncouple T cell anergy, anergic 2C cells were transferred into RAG(-/-) recipients, which resulted in vigorous homeostatic proliferation, recovery of IL-2 production, and acquisition of the ability to reject tumors. Taken together, our data suggest that a major mechanism by which homeostatic proliferation supports tumor rejection is by maintaining and/or re-establishing T cell responsiveness.

Mathematical models of proprioceptors. I. Control and transduction in the muscle spindle.

We constructed a physiologically realistic model of a lower-limb, mammalian muscle spindle composed of mathematical elements closely related to the anatomical components found in the biological spindle. The spindle model incorporates three nonlinear intrafusal fiber models (bag(1), bag(2), and chain) that contribute variously to action potential generation of primary and secondary afferents. A single set of model parameters was optimized on a number of data sets collected from feline soleus muscle, accounting accurately for afferent activity during a variety of ramp, triangular, and sinusoidal stretches. We also incorporated the different temporal properties of fusimotor activation as observed in the twitchlike chain fibers versus the toniclike bag fibers. The model captures the spindle's behavior both in the absence of fusimotor stimulation and during activation of static or dynamic fusimotor efferents. In the case of simultaneous static and dynamic fusimotor efferent stimulation, we demonstrated the importance of including the experimentally observed effect of partial occlusion. The model was validated against data that originated from the cat's medial gastrocnemius muscle and were different from the data used for the parameter determination purposes. The validation record included recently published experiments in which fusimotor efferent and spindle afferent activities were recorded simultaneously during decerebrate locomotion in the cat. This model will be useful in understanding the role of the muscle spindle and its fusimotor control during both natural and pathological motor behavior.

Cross-priming of T cells to intracranial tumor antigens elicits an immune response that fails in the effector phase but can be augmented with local immunotherapy.

Central nervous system (CNS) tumors are thought to be poorly immunogenic. However, whether defective anti-tumor immunity is a consequence of a relative failure of T cell priming versus a deficient effector phase of the anti-tumor immune response is not clear. We utilized a well-defined model system of B16 melanoma expressing the model antigen SIY-GFP to evaluate tumor antigen cross-priming and tumor rejection from the CNS versus subcutaneous compartments. We observed that B16-SIY cells implanted in the CNS were capable of inducing T cell priming as measured by IFN-gamma ELISPOT in the spleen. Cross-priming occurred in the absence of detectable systemic dissemination of the tumor. Despite the induction of a T cell response, CNS tumors grew progressively and were fatal, whereas the same tumor implanted in the flank was rejected. To study the effector phase of the immune response in more detail, in vitro primed 2C/RAG2-/- TCR transgenic CD8+ cells, which recognize the SIY peptide, were adoptively transferred. In addition, the CNS microenvironment was modulated by intracranial delivery of IL-2. While mice that received primed 2C cells alone showed an increase in survival, co-administration of intracranial IL-2 led to a marked prolongation of survival, with 20% of mice surviving at least 120 days. Our results demonstrate that CD8+ T cell cross-priming does indeed occur in response to a CNS tumor, but that manipulation of the brain tumor microenvironment may be necessary to support the effector phase of the anti-tumor immune response.