Malak Kotb

Human Lymphoid and Myeloid Cell Development in NOD/LtSz-scid IL2Rγnull Mice Engrafted with Mobilized Human Hemopoietic Stem Cells

Ethical considerations constrain the in vivo study of human hemopoietic stem cells (HSC). To overcome this limitation, small animal models of human HSC engraftment have been used. We report the development and characterization of a new genetic stock of IL-2R common γ-chain deficient NOD/LtSz-scid (NOD-scid IL2Rγnull) mice and document their ability to support human mobilized blood HSC engraftment and multilineage differentiation. NOD-scid IL2Rγnull mice are deficient in mature lymphocytes and NK cells, survive beyond 16 mo of age, and even after sublethal irradiation resist lymphoma development. Engraftment of NOD-scid IL2Rγnull mice with human HSC generate 6-fold higher percentages of human CD45+ cells in host bone marrow than with similarly treated NOD-scid mice. These human cells include B cells, NK cells, myeloid cells, plasmacytoid dendritic cells, and HSC. Spleens from engrafted NOD-scid IL2Rγnull mice contain human Ig+ B cells and lower numbers of human CD3+ T cells. Coadministration of human Fc-IL7 fusion protein results in high percentages of human CD4+CD8+ thymocytes as well human CD4+CD8− and CD4−CD8+ peripheral blood and splenic T cells. De novo human T cell development in NOD-scid IL2Rγnull mice was validated by 1) high levels of TCR excision circles, 2) complex TCRβ repertoire diversity, and 3) proliferative responses to PHA and streptococcal superantigen, streptococcal pyrogenic exotoxin. Thus, NOD-scid IL2Rγnull mice engrafted with human mobilized blood stem cells provide a new in vivo long-lived model of robust multilineage human HSC engraftment.

DNase Expression Allows the Pathogen Group A Streptococcus to Escape Killing in Neutrophil Extracellular Traps

The innate immune response plays a crucial role in satisfactory host resolution of bacterial infection. In response to chemotactic signals, neutrophils are early responding cells that migrate in large numbers to sites of infection. The recent discovery of secreted neutrophil extracellular traps (NETs) composed of DNA and histones opened a novel dimension in our understanding of the microbial killing capacity of these specialized leukocytes. M1 serotype strains of the pathogen Group A Streptococcus (GAS) are associated with invasive infections including necrotizing fasciitis (NF) and express a potent DNase (Sda1). Here we apply a molecular genetic approach of allelic replacement mutagenesis, single gene complementation, and heterologous expression to demonstrate that DNase Sda1 is both necessary and sufficient to promote GAS neutrophil resistance and virulence in a murine model of NF. Live fluorescent microscopic cell imaging and histopathological analysis are used to establish for the first time a direct linkage between NET degradation and bacterial pathogenicity. Inhibition of GAS DNase activity with G-actin enhanced neutrophil clearance of the pathogen in vitro and reduced virulence in vivo. The results demonstrate a significant role for NETs in neutrophil-mediated innate immunity, and at the same time identify a novel therapeutic target against invasive GAS infection.

Intravenous Immunoglobulin Therapy for Streptococcal Toxic Shock Syndrome—A Comparative Observational Study

Twenty-one consecutive patients with streptococcal toxic shock syndrome (TSS) between December 1994 and April 1995 were treated with a median dose of 2 g of intravenous immunoglobulin (IVIG)/kg (cases) and were compared with 32 patients with streptococcal TSS between 1992 and 1995 who did not receive IVIG therapy (controls). The outcome measure was 30-day survival. Patient plasma was tested for its ability to inhibit T cell activation induced by the infecting strain. The proportion of cases with 30-day survival was higher than that of the controls with 30-day survival (67% vs. 34%, respectively; P = .02). Multivariate analysis revealed that IVIG administration and a lower Acute Physiology and Chronic Health Evaluation II score were associated with survival; the odds ratio for survival associated with IVIG therapy was 8.1 (95% confidence interval, 1.6-45; P = .009). IVIG therapy enhanced the ability of patient plasma to neutralize bacterial mitogenicity and reduced T cell production of interleukin-6 and tumor necrosis factor alpha. IVIG may be an effective adjunctive therapy for streptococcal TSS, possibly because of its ability to neutralize bacterial exotoxins.

Genetic relatedness and superantigen expression in group A streptococcus serotype M1 isolates from patients with severe and nonsevere invasive diseases.

ABSTRACT The relatedness of group A streptococcal (GAS) strains isolated from 35 Canadian patients with invasive disease of different severity was investigated by a variety of molecular methods. All patients were infected with M1T1 strains and, based on clinical criteria, were classified as severe (n = 21) and nonsevere (n = 14) invasive GAS infection cases. All the M1 strains studied had the emm1.0 allele and the same streptococcal pyrogenic exotoxin (Spe) genotype,speA+ speB+ speC speF+speG+ speH smeZ+ ssa. All isolates had the same speA allotype, speA2. The randomly amplified polymorphic DNA banding pattern with two different primers was identical for all strains, and pulsed field gel electrophoresis analysis showed that 33 and 30 isolates had identical banding patterns after DNA digestion with SfiI or SmaI, respectively; the nonidentical isolates differed from the main pattern by only one band. A relatively high degree of polymorphism in specific regions of the sic gene was observed among isolates; however, this polymorphism was not associated with disease severity. Likewise, although the phenotypic expression of SpeA, SpeB, and SpeF proteins varied among the M1T1 isolates, there was no correlation between the amount of Spe expressed and disease severity. Importantly, mitogenic and cytokine responses induced by partially purified bacterial culture supernatants containing a mixture of expressed superantigens were very similar for isolates from severe and nonsevere cases (P > 0.1). Together, the data indicate that highly related invasive M1T1 isolates, some indistinguishable, can cause disease of varying severity in different individuals. These findings underscore the contribution of host factors to the outcome of invasive GAS infections.

Amelioration of the physiologic and biochemical changes of acute pancreatitis using an anti-TNF-α polyclonal antibody☆☆☆

Tumor necrosis factor (TNF) is an inflammatory cytokine that may be an important mediator in the development of the systemic sequelae associated with severe acute pancreatitis. The purpose of this study was to determine whether the neutralization of TNF-alpha with a polyclonal antibody could ameliorate selected biochemical parameters of severe pancreatitis in a rat model. Pancreatitis was induced by an antegrade injection of artificial bile into the bile duct. Forty rats were randomized into 4 groups: no surgery (controls), saline infusion to bile duct (sham), placebo treatment in animals with pancreatitis (placebo + Px), and pretreatment with a polyclonal antibody (PAb) in animals with pancreatitis (PAb + Px). Serum TNF-alpha, amylase, calcium, hematocrit, glucose, and ascites volume were measured 2 hours after bile duct infusion. Pretreatment with the PAb produced a significant improvement in all parameters when compared with pancreatitis animals treated with placebo (p < 0.001). In addition, TNF-alpha, which was elevated in animals with pancreatitis, was reduced significantly in treated animals (p < 0.001). These results suggest that TNF-alpha may be an important mediator in the evolution of the systemic manifestations of severe acute pancreatitis.

The Effect of CYP3A5 and MDR1 Polymorphic Expression on Cyclosporine Oral Disposition in Renal Transplant Patients

Variability in CYP3A (CYP3A4/5) and P‐glycoprotein (human MDR1 gene product) activity underlies interindividual differences in oral cyclosporine (CsA) bioavailability. Racial differences in polymorphic expression of CYP3A5 and MDR1 may explain observed interracial variability in oral bioavailability. Our objective was to evaluate the effect of CYP3A5 and MDR1 polymorphic expression on CsA oral disposition. Steady‐state plasma concentration profiles (n = 19) were sampled in renal transplant recipients receiving concentration‐adjusted CsA maintenance therapy. CsA plasma concentrations were measured by fluorescence polarization immunoassay. CYP3A5 and MDR1 genotypes were determined by real‐time polymerase chain reaction. Noncompartmental pharmacokinetic analysis and nonlinear mixed‐effects modeling (NONMEM) were performed to assess the effect of genotype on CsA pharmacokinetics. MDR1 C3435T genotype was identified as the best predictor of CsA systemic exposure. CsA oral clearance was significantly higher in subjects who carried at least one 3435T allele compared to homozygous wild‐type individuals (40.0 ± 2.2 vs. 26.4 ± 3.1 L/h, p = 0.007). MDR1 C3435T genotype accounted for 43% of the interindividual variability of CsA oral clearance in the study population after accounting for interoccasion variability. The authors were unable to independently assess whether CYP3A5 correlated with any CsA pharmacokinetic parameter since all CYP3A5 nonexpressors were also 3435T allele carriers. MDR1 3435T allele carriers have enhanced oral clearance compared to individuals with the CC genotype. The frequency of the 3435T allele is lower in African Americans compared to Caucasians. Thus, the MDR1 C3435T genotype offers a potential mechanistic basis to explain interracial differences in CsA oral bioavailability. Further studies are needed to explore the relationship between CYP3A5 and MDR1 genotype and phenotype.

Inverse Relation between Disease Severity and Expression of the Streptococcal Cysteine Protease, SpeB, among Clonal M1T1 Isolates Recovered from Invasive Group A Streptococcal Infection Cases

ABSTRACT The streptococcal cysteine protease (SpeB) is one of the major virulence factors produced by group A streptococci (GAS). In this study we investigated if differences exist in SpeB production by clonally related M1T1 clinical isolates derived from patients with invasive infections. Twenty-nine of these isolates were from nonsevere cases and 48 were from severe cases, including streptococcal toxic shock syndrome (STSS) and necrotizing fasciitis (NF) cases. The expression and amount of the 28-kDa SpeB protein produced were determined by quantitative Western blotting, and protease activity was measured by a fluorescent enzymatic assay. A high degree of variation in SpeB expression was seen among the isolates, and this variation seemed to correlate with the severity and/or clinical manifestation of the invasive infection. The mean amount of 28-kDa SpeB protein and cysteine protease activity produced by isolates from nonsevere cases was significantly higher than that from STSS cases (P = 0.001). This difference was partly due to the fact that 41% of STSS isolates produced little or no SpeB compared to only 14% of isolates recovered in nonsevere cases. Moreover, the cysteine protease activity among those isolates that expressed SpeB was significantly lower for STSS isolates than for isolates from nonsevere cases (P = 0.001). Increased SpeB production was also inversely correlated with intact M protein expression, and inhibition of cysteine protease activity blocked the cleavage of the surface M protein. Together, the data support the existence of both an “on-off” and a posttranslational regulatory mechanism(s) controlling SpeB production, and they suggest that isolates with the speB gene in the “off” state are more likely to spare the surface M protein and to be isolated from cases of severe rather than nonsevere invasive infection. These findings may have important implications for the role of SpeB in host-pathogen interactions via regulation of the expression of GAS virulence genes and the severity of invasive disease.

Anti-TNFα therapy improves survival and ameliorates the pathophysiologic sequelae in acute pancreatitis in the rat

BACKGROUND Elevated levels of tumor necrosis factor-alpha (TNFalpha) have been measured in a lethal model acute pancreatitis (AP) and may contribute to the pathophysiologic sequelae of the disease. METHODS To determine the significance of anti-TNFalpha therapy on survival and disease manifestations in a clinically relevant model of AP, a rat model was developed using a retrograde pancreatic ductal infusion of bile. Animals were randomized to no treatment (n = 30) or treatment with anti-TNFalpha antibody 15 minutes prior to induction of AP (n = 30). Five treated and 5 untreated rats were killed at various time periods up to 72 hours to provide temporal characterization of TNFalpha activity in AP. RESULTS A burst Of TNFalpha activity in the serum of untreated pancreatitis animals between 1 and 3 hours after induction of the disease is prevented by pretreatment with anti-TNFalpha antibody. CONCLUSIONS These findings provide a plausible mechanism for the improvement in biochemical and histologic parameters as well as in overall survival in an experimental model of acute pancreatitis in the rat.

Mutational analysis of the group A streptococcal operon encoding streptolysin S and its virulence role in invasive infection

The pathogen group A Streptococcus (GAS) produces a wide spectrum of infections including necrotizing fasciitis (NF). Streptolysin S (SLS) produces the hallmark β‐haemolytic phenotype produced by GAS. The nine‐gene GAS locus (sagA–sagI) resembling a bacteriocin biosynthetic operon is necessary and sufficient  for  SLS  production.  Using  precise,  in‐frame allelic exchange mutagenesis and single‐gene complementation, we show sagA, sagB, sagC, sagD, sagE, sagF and sagG are each individually required for SLS production, and that sagE may further serve an immunity function. Limited site‐directed mutagenesis of specific amino acids in the SagA prepropeptide supports the designation of SLS as a bacteriocin‐like toxin. No significant pleotrophic effects of sagA deletion were observed on M protein, capsule or cysteine protease production. In a murine model of NF, the SLS‐negative M1T1 GAS mutant was markedly diminished in its ability to produce necrotic skin ulcers and spread to the systemic circulation. The SLS toxin impaired phagocytic clearance and promoted epithelial cell cytotoxicity, the latter phenotype being enhanced by the effects of M protein and streptolysin O. We conclude that all genetic components of the sag operon are required for expression of functional SLS, an important virulence factor in the pathogenesis of invasive M1T1 GAS infection.

Host Genetic Variation Affects Resistance to Infection with a Highly Pathogenic H5N1 Influenza A Virus in Mice

ABSTRACT Despite the prevalence of H5N1 influenza viruses in global avian populations, comparatively few cases have been diagnosed in humans. Although viral factors almost certainly play a role in limiting human infection and disease, host genetics most likely contribute substantially. To model host factors in the context of influenza virus infection, we determined the lethal dose of a highly pathogenic H5N1 virus (A/Hong Kong/213/03) in C57BL/6J and DBA/2J mice and identified genetic elements associated with survival after infection. The lethal dose in these hosts varied by 4 logs and was associated with differences in replication kinetics and increased production of proinflammatory cytokines CCL2 and tumor necrosis factor alpha in susceptible DBA/2J mice. Gene mapping with recombinant inbred BXD strains revealed five loci or Qivr (quantitative trait loci for influenza virus resistance) located on chromosomes 2, 7, 11, 15, and 17 associated with resistance to H5N1 virus. In conjunction with gene expression profiling, we identified a number of candidate susceptibility genes. One of the validated genes, the hemolytic complement gene, affected virus titer 7 days after infection. We conclude that H5N1 influenza virus-induced pathology is affected by a complex and multigenic host component.