Rabbit Model for Superantigen-Mediated Lethal Pulmonary Disease.

Staphylococcus aureus is a highly significant cause of serious human infections in the USA. Many of these illnesses are mediated by interactions between the host immune system and staphylococcal superantigens (SAgs). Several of these severe staphylococcal infections are initiated in the lungs, making this an important site to study. Here, we describe the rabbit model for investigating the role of staphylococcal SAgs in pulmonary-associated lethal infection and intoxication.

Differential Induction of Type I and Type III Interferons by Swine and Human Origin H1N1 Influenza A Viruses in Porcine Airway Epithelial Cells.

Interferons (IFNs) have been shown to inhibit influenza A virus (IAV) replication and play an essential role in controlling viral infection. Here we studied the kinetics and magnitude of induction of type I and type III IFN transcripts by primary porcine airway epithelial cells (pAECs) in response to swine and human origin IAV. We observed that swine influenza viruses (SIV) replicate more efficiently than the human pandemic influenza A/California/2009 (pH1N1 CA/09) in pAECs. Interestingly, we also found significant difference in kinetics of IFN-ß, IFN-λ1 and IFN-λ3 gene expression by these viruses. While there was delay of up to 12 hours post infection (h p.i.) in induction of IFN genes in pAECs infected with swine IAV A/Sw/Illinois/2008 (H1N1 IL/08), human pH1N1 CA/09 rapidly induced IFN-ß, IFN-λ1 and IFN-λ3 gene expression as early as 4 h p.i. However, the magnitude of IFN-ß and IFN-λ3 induction at 24 h p.i. was not significantly different between the viral strains tested. Additionally, we found that swine H1N1 IL/08 was less sensitive to dsRNA induced antiviral response compared to human pH1N1 CA/09. Our data suggest that the human and swine IAVs differ in their ability to induce and respond to type I and type III interferons in swine cells. Swine origin IAV may have adapted to the pig host by subverting innate antiviral responses to viral infection.

Activated CD8+ T lymphocytes inhibit neural stem/progenitor cell proliferation: role of interferon-gamma.

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.

Modulation of neural stem/progenitor cell proliferation during experimental Herpes Simplex encephalitis is mediated by differential FGF-2 expression in the adult brain.

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 days post infection (p.i.). However, by 15 days p.i. the nestin(+) population decreased significantly below levels observed in uninfected brains and remained depressed through 30 days p.i. This initial increase in NSC population occurred concurrently with increased brain cell proliferation, which peaked at 3 days p.i. On closer examination, we found that while actively proliferating Sox2(+) NSCs increased in number at 6 days p.i., proliferating DCX(+) neuroblasts contributed to the increased response at 3 days p.i. However, overall proliferation decreased steadily from 15 days 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 days p.i. and was robustly down-regulated at 15 days 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 days 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.

Staphylococcal superantigens cause lethal pulmonary disease in rabbits.

BACKGROUND: The Centers for Disease Control and Prevention (CDC) and others reported that methicillin-resistant S. aureus (MRSA) are significant causes of serious human infections, including pulmonary illnesses. We investigated the role played by superantigens in lung-associated lethal illness in rabbits. METHODS: A rabbit model was established to investigate the potential role played by superantigens, staphylococcal enterotoxin B (SEB), staphylococcal enterotoxin C (SEC), and toxic shock syndrome toxin-1 (TSST-1). Rabbits received intrabronchial community-associated (CA) MRSA strains USA200 (TSST-1(+)), MW2 (SEC(+)), c99-529 (SEB(+)), or purified superantigens. Some rabbits were preimmunized against superantigens or treated with soluble high-affinity T cell receptors (Vß-TCR) to neutralize SEB and then challenged intrabronchially with CA-MRSA or superantigens. RESULTS: Rabbits challenged with CA-MRSA or superantigens developed fatal, pulmonary illnesses. Animals preimmunized against purified superantigens, or treated passively with Vß-TCRs and then challenged with CA-MRSA or superantigens, survived. Lung histological analysis indicated that nonimmune animals developed lesions consistent with necrotizing pneumonia after challenge with CA-MRSA or purified superantigens. Superantigen-immune animals or animals treated with soluble Vß-TCRs did not develop pulmonary lesions. CONCLUSIONS: Superantigens contribute to lethal pulmonary illnesses due to CA-MRSA; preexisting immunity to superantigens prevents lethality. Administration of high-affinity Vß-TCR with specificity for SEB to nonimmune animals protects from lethal pulmonary illness resulting from SEB(+) CA-MRSA and SEB.

Extreme pyrexia and rapid death due to Staphylococcus aureus infection: analysis of 2 cases.

We describe unusual Staphylococcus aureus infections in 2 patients. The infections were 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.