SummaryMycobacterium ulcerans produces an extracellular cutaneous infection (Buruli ulcer) characterized by immunosuppression. This is in stark contrast to all other pathogenic Mycobacteria species that cause intracellular, granulomatous infections. The unique mycobacterial pathology of M. ulcerans infection is attributed to a plasmid-encoded immunomodulatory macrolide toxin, mycolactone. In this article we explore the role of mycolactone in the virulence of M. ulcerans using mycolactone and genetically defined mycolactone negative mutants. In a guinea pig infection model wild-type (WT) M. ulcerans produces an extracellular infection whereas mycolactone negative mutants produce an intracellular inflammatory infection similar to that of Mycobacterium marinum . Although mycolactone negative mutants are avirulent, they persist for at least 6 weeks. Chemical complementation of M. ulcerans mutants with mycolactone restores WT M. ulcerans pathology. Mycolactone negative mutants are capable of growth within macrophages in vitro whereas macrophages are killed by WT M. ulcerans . The ability of mycolactone to caused delayed cell death via apoptosis has been reported. However, mycolactone also causes cell death via necrosis. In vitro mycolactone has antiphagocytic properties. Neither WT M. ulcerans nor mycolactone negative strains are strong neutrophil attractants. These results suggest that mycolactone is largely responsible for the unique pathology produced by M. ulcerans .

The murine cytomegalovirus CC chemokine homolog MCK-2 (m131-129) is an important determinant of dissemination during primary infection. Reduced peak levels of viremia at day 5 were followed by reduced levels of virus in salivary glands starting at day 7 when mck insertion (RM461) and point (RM4511) mutants were compared to mck-expressing viruses. A dramatic MCK-2-enhanced inflammation occurred at the inoculation site over the first few days of infection, preceding viremia. The data further reinforce the role of MCK-2 as a proinflammatory signal that recruits leukocytes to increase the efficiency of viral dissemination in the host.

Diabetes mellitus results from immune cell invasion into pancreatic islets of Langerhans, eventually leading to selective destruction of the insulin-producing ␤-cells. How this process is initiated is not well understood. In this study, we investigated the regulation of the CXCL1 and CXCL2 genes, which encode proteins that promote migration of CXCR2 ϩ cells, such as neutrophils, toward secreting tissue. Herein, we found that IL-1␤ markedly enhanced the expression of the CXCL1 and CXCL2 genes in rat islets and ␤-cell lines, which resulted in increased secretion of each of these proteins. CXCL1 and CXCL2 also stimulated the expression of specific integrin proteins on the surface of human neutrophils. Mutation of a consensus NF-B genomic sequence present in both gene promoters reduced the ability of IL-1␤ to promote transcription. In addition, IL-1␤ induced binding of the p65 and p50 subunits of NF-B to these consensus B regulatory elements as well as to additional B sites located near the core promoter regions of each gene. Additionally, serine-phosphorylated STAT1 bound to the promoters of the CXCL1 and CXCL2 genes. We further found that IL-1␤ induced specific posttranslational modifications to histone H3 in a time frame congruent with transcription factor binding and transcript accumulation. We conclude that IL-1␤-mediated regulation of the CXCL1 and CXCL2 genes in pancreatic ␤-cells requires stimulus-induced changes in histone chemical modifications, recruitment of the NF-B and STAT1 transcription factors to genomic regulatory sequences within the proximal gene promoters, and increases in phosphorylated forms of RNA polymerase II.

Postmortem succession of human-associated microbial communities ("human microbiome") has been suggested as a possible method for estimating postmortem interval (PMI) for forensic analyses. Here we evaluate human gut bacterial populations to determine quantifiable, time-dependent changes postmortem. Gut microflora were repeatedly sampled from the proximal large intestine of 12 deceased human individuals as they decayed under environmental conditions. Three intestinal bacterial genera were quantified by quantitative PCR (qPCR) using group-specific primers targeting 16S rRNA genes. Bacteroides and Lactobacillus relative abundances declined exponentially with increasing PMI at rates of Nt=0.977e(-0.0144t) (r2=0.537, p<0.001) and Nt=0.019e(-0.0087t) (r2=0.396, p<0.001), respectively, where Nt is relative abundance at time (t) in cumulative degree hours. Bifidobacterium relative abundances did not change significantly: Nt=0.003e(-0.002t) (r2=0.033, p=0.284). Therefore, Bacteroides and Lactobacillus abundances could be used as quantitative indicators of PMI.

IntroductionHuman cytomegalovirus (HCMV) is an opportunistic pathogen of widespread medical importance, causing congenital disease following a primary infection during pregnancy, as well as a wide range of organ-specific diseases following reactivation in immunocompromised patients. 1 Murine CMV (MCMV) has proven to be an excellent model of HCMV infection and disease, providing information on the basic patterns of pathogenesis, latency, immunity, and dissemination. 2-4 Dissemination of HCMV or MCMV requires a population of host mononuclear leukocytes that traverse the bloodstream. [5][6][7] Based on comparisons of wild-type and mutant MCMV-infected mice, MCMV enhances dissemination levels by expressing a pro-inflammatory chemokine-like gene product called MCMV chemokine (MCK). 2,7,8 MCK appears to increase the recruitment of leukocytes to initial sites of infection and to allow a greater number of virus-positive leukocytes to traverse the bloodstream to salivary glands (SGs), 3,7 a site of prolonged replication and shedding. This process likely provides a source of virus for transmission to naive mice. 2 The human pathogen HCMV also encodes chemokine homologs: one CC chemokine homolog (UL128) that may be analogous to MCK, 9 as well as one very potent CXC chemokine (gpUL146/vCXCL1) that is as potent as human interleukin-8 (IL-8) and acts via CXCR2. 10 The carboxyl terminal 81 aa m131 ORF encodes a predicted gene product, MCK-1, 8 that elicits both calcium mobilization and adherence in resident or elicited peritoneal exudate cells (PECs). 11 mRNA splicing adds 199 aa to this chemokine-like domain to make MCK-2 the natural, secreted gene product. 12 Studies on virusinfected mice have suggested that MCK-2 influences levels of viremia as well as patterns of dissemination 11,13 by increasing the inflammatory response at sites of infection. 14 An MCK-2-dependent influx of leukocytes into initial sites of infection is followed by a mononuclear-cell (MNC)-associated viremia that peaks at day 5 after infection 14 and leads to viral seeding of the SGs. 2,15-17 Although MCK-2 is pro-inflammatory and a determinant of both viremia and dissemination 11,14 and was also associated with both natural killer and adaptive immune defects, 13 this chemokinelike function is not involved in immune evasion. On the one hand, MCK-2 control of viremia and dissemination is preserved in mice that lack the ability to mount an adaptive immune response. 2,16 On the other hand, virus replication levels and clearance from inoculated foot pads (FPs) or sites of systemic infection, including 11,16,17,[20][21][22][23] and latency 22,24,25 ; however, these cells also have been implicated in host defense. 20,23,[26][27][28] The differentiation-dependent susceptibility of monocytes and macrophages to MCMV infection 22,23 has led to a consensus view that nonpermissive monocytes may disseminate infection and differentiate into permissive mature cells upon entry into tissues. This pattern is similar to that proposed to explain viral reactivation from lat...