Background The CDC et al. reported methicillin-resistant S. aureus (MRSA) are significant causes of serious human infections, including pulmonary illnesses. We investigated the role of superantigens (SAgs) in lung-associated lethal illness in rabbits. Methods A rabbit model was established to investigate the potential role of SAgs, staphylococcal enterotoxin (SE) B and SEC, and toxic shock syndrome toxin-1 (TSST-1). Rabbits received intra-bronchial community-associated (CA) MRSA strains USA200 (TSST-1+), MW2 (SEC+), or c99-529 (SEB+), or purified SAgs. Some rabbits were pre-immunized against SAgs or treated with soluble high-affinity T cell receptors (Vβ-TCR) to neutralize SEB and then challenged intra-bronchially with CA-MRSA or SAgs. Results Rabbits challenged with CA-MRSA or SAgs developed fatal, pulmonary illnesses. Animals pre-immunized against purified SAgs, or treated passively with Vβ-TCRs, and then challenged with CA-MRSA or SAgs, survived. Lung histology indicated non-immune animals developed lesions consistent with necrotizing pneumonia after challenge with CA-MRSA or purified SAgs. SAg immune animals or animals treated with soluble Vβ-TCRs did not develop pulmonary lesions. Conclusions SAgs contribute to lethal pulmonary illneses due to CA-MRSA; pre-existing immunity to SAgs prevents lethality. Administration of high-affinity Vβ-TCR with specificity for SEB to non-immune animals protects from lethal pulmonary illness due to SEB+ CA-MRSA and SEB.

Despite the high prevalence and devastating outcome, there remain a few options for treatment of ischemic stroke. Currently available treatments are limited by a short time window for treatment and marginal efficacy when used. We have tested a human umbilical cord blood-derived stem cell line that has been shown to result in a significant reduction in stroke infarct volume as well as improved functional recovery following stroke in the rat. In the present study we address the mechanism of action and compared the therapeutic efficacy of high- versus low-passage nonhematopoietic umbilical cord blood stem cells (nh-UCBSCs). Using the middle cerebral arterial occlusion (MCAo) model of stroke in Sprague-Dawley rats, we administered nh-UCBSC by intravenous (IV) injection 2 days following stroke induction. These human cells were injected into rats without any immune suppression, and no adverse reactions were detected. Both behavioral and histological analyses have shown that the administration of these cells reduces the infarct volume by 50% as well as improves the functional outcome of these rats following stroke for both high- and low-passaged nh-UCBSCs. Flow cytometry analysis of immune cells present in the brains of normal rats, rats with ischemic brain injury, and ischemic animals with nh-UCBSC treatment confirmed infiltration of macrophages and T cells consequent to ischemia and reduction to normal levels with nh-UCBSC treatment. Flow cytometry also revealed a restoration of normal levels of microglia in the brain following treatment. These data suggest that nh-UCBSCs may act by inhibiting immune cell migration into the brain from the periphery and possibly by inhibition of immune cell activation within the brain. nh-UCBSCs exhibit great potential for treatment of stroke, including the fact that they are associated with an increased therapeutic time window, no known ill-effects, and that they can be expanded to high numbers for, and stored for, treatment.

The ability of neural stem/progenitor cells (NSCs) to self-renew, migrate to damaged sites, and differentiate into neurons has renewed interest in using them in therapies for neurodegenerative disorders. Neurological diseases, including viral infections of the brain, are often accompanied by chronic inflammation, whose impact on NSC function remains unexplored. We have previously shown that chronic neuroinflammation, a hallmark of experimental herpes simplex encephalitis (HSE) in mice, is dominated by brain-infiltrating activated CD8 T-cells. In the present study, activated CD8 lymphocytes were found to suppress NSC proliferation profoundly. Luciferase positive (luc+) NSCs co-cultured with activated, MHC-matched, CD8+ lymphocytes (luc−) showed two- to five-fold lower luminescence than co-cultures with un-stimulated lymphocytes. On the other hand, similarly activated CD4+ lymphocytes did not suppress NSC growth. This differential lymphocyte effect on proliferation was confirmed by decreased BrdU uptake by NSC cultured with activated CD8 T-cells. Interestingly, neutralizing antibodies to interferon-gamma (IFN-γ) reversed the impact of CD8 lymphocytes on NSCs. Antibodies specific to the IFN-γ receptor-1 subunit complex abrogated the inhibitory effects of both CD8 lymphocytes and IFN-γ, indicating that the inhibitory effect of these cells was mediated by IFN-γ in a receptor-specific manner. In addition, activated CD8 lymphocytes decreased levels of nestin and Sox2 expression in NSCs while increasing GFAP expression, suggesting possible induction of an altered differentiation state. Furthermore, NSCs obtained from IFN-γ receptor-1 knock-out embryos were refractory to the inhibitory effects of activated CD8+ T lymphocytes on cell proliferation and Sox2 expression. Taken together, the studies presented here demonstrate a role for activated CD8 T-cells in regulating NSC function mediated through the production of IFN-γ. This cytokine may influence neuro-restorative processes and ultimately contribute to the long-term sequelae commonly seen following herpes encephalitis.

Neural stem cells (NSCs) respond to inflammatory cues induced during brain injury and are thought to be involved in recovery from brain damage. Little is known about NSC response during brain infections. The present study evaluated NSC proliferation during Herpes Simplex Virus-1 brain infection. Total numbers of nestin(+) NSCs increased significantly in infected brains at 6 d post infection (p.i.). However, by 15 d p.i. the nestin(+) population decreased significantly below levels observed in uninfected brains and remained depressed through 30 d p.i.. This initial increase in NSC population occurred concurrently with increased brain cell proliferation, which peaked at 3 d p.i.. On closer examination, we found that while actively proliferating Sox2(+) NSCs increased in number at 6 d p.i., proliferating DCX(+) neuroblasts contributed to the increased response at 3 d p.i.. However, overall proliferation decreased steadily from 15 d p.i. to below control levels. To determine the mechanisms involved in altering NSC proliferation, neurotrophin and growth factor expression profiles were assessed. FGF-2 gene expression increased at 5 d p.i. and was robustly down-regulated at 15 d p.i. (>1000 fold), which was further confirmed by increased FGF-2 immunostaining around the lateral ventricles. Furthermore, supplementing infected animals with recombinant FGF-2, at 15 d p.i., significantly increased the number of proliferating brain cells. These findings demonstrate that the temporal changes in NSC proliferation are mediated through the regulation of FGF-2 and that the NSC niche may benefit from supplementation with FGF-2 during HSV-1 brain infection.

Unusual Staphylococcus aureus infections in two patients are described. The infections are characterized by extreme pyrexia and rapid death. Both causative organisms produced a deletion mutant form of toxic shock syndrome toxin-1 and variant enterotoxin C which may have caused pyrexia and death.