Lymphocyte apoptosis plays a central role in the pathophysiology of sepsis. Lymphocyte apoptosis was examined in mice with defective death receptor pathways due to transgenic expression of a dominant negative mutant of Fas-associated death domain (FADD-DN) or Bid-/- and in mice with defective mitochondrial-mediated pathways due to loss of Bim-/-, Puma-/-, or Noxa-/-. FADD-DN transgenic and Bid-/- mice had significant albeit incomplete protection, and this protection was associated with increased survival. Surprisingly, splenic B cells were also protected in FADD-DN mice although transgene expression was confined to T cells, providing evidence for an indirect protective mechanism. Bim-/- provided virtually complete protection against lymphocyte apoptosis whereas Puma-/- and Noxa-/- mice had modest or no protection, respectively. Bim-/- mice had improved survival, and adoptive transfer of splenocytes from Bim-/- mice into Rag 1-/- mice demonstrated that this was a lymphocyte intrinsic effect. The improved survival was associated with decreased interleukin (IL) -10 and IL-6 cytokines. Collectively, these data indicate that numerous death stimuli are generated during sepsis, and it therefore appears unlikely that blocking a single "trigger" can inhibit apoptosis. If siRNA becomes practical therapeutically, proapoptotic proteins would be potential targets.

Traumatic brain injury (TBI) results in rapid recruitment of leukocytes into the injured brain. Monocytes constitute a significant proportion of the initial infiltrate and have the potential to propagate secondary brain injury or generate an environment of repair and regeneration. Monocytes are a diverse population of cells (classical, intermediate and non-classical), with distinct functions, however, the recruitment order of these subpopulations to the injured brain is largely remains unknown. Thus, we examined which monocyte subpopulations are required for the generation of early inflammatory infiltrate within the injured brain, and whether their depletion attenuates secondary injury or neurocognitive outcome. Global monocyte depletion correlated with significant improvements in brain edema, motor coordination, and working memory, and abrogated neutrophil infiltration into the injured brain. However, targeted depletion of classical monocytes alone had no effect on neutrophil recruitment to the site of injury, implicating the non-classical monocyte in this process. In contrast, mice that have markedly reduced numbers of non-classical monocytes (CX3CR1−/−) exhibited a significant reduction in neutrophil infiltration into the brain after TBI as compared to control mice. Our data suggest a critical role for non-classical monocytes in the pathology of TBI in mice, including important clinical outcomes associated with mortality in this injury process.

Apoptosis is a key pathogenic mechanism in sepsis that induces extensive death of lymphocytes and dendritic cells, thereby contributing to the immunosuppression that characterizes the septic disorder. Numerous animal studies indicate that prevention of apoptosis in sepsis improves survival and may represent a potential therapy for this highly lethal disorder. Recently, novel cell-penetrating peptide constructs such as HIV-1 TAT basic domain and related peptides have been developed to deliver bioactive cargoes and peptides into cells. In the present study, we investigated the effects of sepsis-induced apoptosis in Bcl-xL transgenic mice and in wild-type mice treated with an antiapoptotic TAT-Bcl-xL fusion protein and TAT-BH4 peptide. Lymphocytes from Bcl-xL transgenic mice were resistant to sepsis-induced apoptosis, and these mice had a ∼3-fold improvement in survival. TAT-Bcl-xL and TAT-BH4 prevented Escherichia coli-induced human lymphocyte apoptosis ex vivo and markedly decreased lymphocyte apoptosis in an in vivo mouse model of sepsis. In conclusion, TAT-conjugated antiapoptotic Bcl-2-like peptides may offer a novel therapy to prevent apoptosis in sepsis and improve survival.

Background The complex alterations that occur in peripheral immunity after traumatic brain injury (TBI) have been poorly characterized to date. The purpose of this study was to determine the temporal changes in the peripheral immune response after TBI in a murine model of closed head injury. Methods C57Bl/6 mice underwent closed head injury via a weight drop technique (n=5) vs. sham injury (n=3) per time point. Blood, spleen, and thymus were collected and immune phenotype, cytokine expression, and antibody production were determined via flow cytometry and multiplex immunoassays at 1, 3, 7, 14, 30, and 60 days post injury. Results TBI results in acute and chronic changes in both the innate and adaptive immune response. TBI resulted in a striking loss of thymocytes as early as 3 days post-injury (2.1×107 TBI vs. 5.6×107 sham, p=0.001). Similarly, blood monocyte counts were markedly diminished as early as 24 hours post-TBI (372/dl TBI vs. 1359/dl sham, p=0.002) and remained suppressed throughout the first month post-injury. At 60 days post-injury monocytes were polarized towards an anti-inflammatory (M2) phenotype. TBI also resulted in diminished IL-12 expression from day 14 post-injury throughout the remainder of the observation period. Conclusion TBI results in temporal changes in both the peripheral and central immune systems culminating in an overall immune suppressed phenotype and anti-inflammatory milieu. Level of Evidence Level 1 prospective randomized controlled animal experiment.

Microglia are the resident innate immune cells of the brain. Although embryologically and functionally distinct, they are morphologically similar to peripheral monocyte-derived cells resulting in a poor ability to discriminate between the two cell types. The purpose of this study was to develop a rapid and reliable method to simultaneously characterize, quantify, and discriminate between whole populations of myeloid cells from the brain in a murine model of traumatic brain injury (TBI). Male C57BL/6 mice underwent TBI (n=16) or sham injury (n=14). Brains were harvested at 24 hours post injury. Multiparameter flow cytometry and sequential gating analysis was performed allowing for discrimination between microglia and infiltrating leukocytes as well as for the characterization and quantification of individual subtypes within the infiltrating population. The proportion of infiltrating leukocytes within the brain increased with the severity of injury and the predominate cell types within the infiltrating population were monocyte-derived (p=0.01). Additionally, the severity of injury altered the overall makeup of the infiltrating monocyte-derived cells. In conclusion, we describe a flow cytometry based technique for gross discrimination between infiltrating leukocytes and microglia as well as the ability to simultaneously characterize and quantify individual myeloid subtypes and their maturation states within these populations.