Pyelonephritogenic diffusely adhering Escherichia coli EC7372 harboring Dr-II adhesin carries classical uropathogenic virulence genes and promotes cell lysis and apoptosis in polarized epithelial caco-2/TC7 cells

Typical and Atypical Enteroaggregative Escherichia coli Are Both Virulent in the Galleria mellonella Model

Enteroaggregative Escherichia coli (EAEC) is an emerging pathotype responsible for acute and persistent diarrhea. It can be classified as typical and atypical strains, respectively, based on the presence or absence of the AggR regulon, suggesting a higher virulence for typical EAEC. This study aims to evaluate in the Galleria mellonella model if there are differences in the virulence profiles among clinical strains of typical and atypical EAEC, prototype strains EAEC C1096, 042 and its aggR mutant. The clinical EAEC strains (n = 20) were analyzed for the presence of 22 putative virulence factors of EAEC or extraintestinal E. coli by PCR, as well as phenotypic characteristics of virulence (enzymes, siderophore, and biofilm). The survival of the larvae was analyzed after inoculation of 10⁴-10⁷ CFU/larva; the monitoring of bacterial growth in vivo and hemocyte quantification was determined after inoculation of the prototype strains (10⁵ CFU/larva) at different periods after infection. The strains of typical and atypical EAEC presented the same virulence profile for the larva, regardless of the amount or type of genes and phenotypic aspects of virulence analyzed. In addition, the EAEC 042 aggR mutant strain showed a significant reduction in the mortality of the inoculated larvae compared to the wild-type strain. In conclusion, the results obtained herein demonstrate that the virulence of EAEC seems to be related to the AggR regulon, but not exclusively, and atypical EAEC strains may be as virulent as typical ones in vivo in the G. mellonella model.

Pathoadaptive Mutations in Uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) are opportunistic human pathogens that primarily circulate as part of commensal intestinal microbiota. Though they have the ability to survive and proliferate in various urinary tract compartments, the urinary tract is a transient, occasional habitat for UPEC. Because of this, most of the UPEC traits have originally evolved to serve in intestinal colonization and transmission. Some of these bacterial traits serve as virulence factors - they are critical to or assist in survival of UPEC as pathogens, and the structure and/or function may be specialized for the infection. Other traits could serve as anti-virulence factors - they represent liability in the urinary tract and are under selection to be lost or inactivated during the infection. Inactivation, variation, or other changes of the bacterial genes that increase the pathogen's fitness during the infection are called pathoadaptive mutations. This chapter describes examples of pathoadaptive mutations in UPEC and provides rationale for their further in-depth study.

Pathogenesis of human diffusely adhering Escherichia coli expressing Afa/Dr adhesins (Afa/Dr DAEC): current insights and future challenges

The pathogenicity and clinical pertinence of diffusely adhering Escherichia coli expressing the Afa/Dr adhesins (Afa/Dr DAEC) in urinary tract infections (UTIs) and pregnancy complications are well established. In contrast, the implication of intestinal Afa/Dr DAEC in diarrhea is still under debate. These strains are age dependently involved in diarrhea in children, are apparently not involved in diarrhea in adults, and can also be asymptomatic intestinal microbiota strains in children and adult. This comprehensive review analyzes the epidemiology and diagnosis and highlights recent progress which has improved the understanding of Afa/Dr DAEC pathogenesis. Here, I summarize the roles of Afa/Dr DAEC virulence factors, including Afa/Dr adhesins, flagella, Sat toxin, and pks island products, in the development of specific mechanisms of pathogenicity. In intestinal epithelial polarized cells, the Afa/Dr adhesins trigger cell membrane receptor clustering and activation of the linked cell signaling pathways, promote structural and functional cell lesions and injuries in intestinal barrier, induce proinflammatory responses, create angiogenesis, instigate epithelial-mesenchymal transition-like events, and lead to pks-dependent DNA damage. UTI-associated Afa/Dr DAEC strains, following adhesin-membrane receptor cell interactions and activation of associated lipid raft-dependent cell signaling pathways, internalize in a microtubule-dependent manner within urinary tract epithelial cells, develop a particular intracellular lifestyle, and trigger a toxin-dependent cell detachment. In response to Afa/Dr DAEC infection, the host epithelial cells generate antibacterial defense responses. Finally, I discuss a hypothetical role of intestinal Afa/Dr DAEC strains that can act as "silent pathogens" with the capacity to emerge as "pathobionts" for the development of inflammatory bowel disease and intestinal carcinogenesis.

Pathogenesis of human enterovirulent bacteria: lessons from cultured, fully differentiated human colon cancer cell lines

Hosts are protected from attack by potentially harmful enteric microorganisms, viruses, and parasites by the polarized fully differentiated epithelial cells that make up the epithelium, providing a physical and functional barrier. Enterovirulent bacteria interact with the epithelial polarized cells lining the intestinal barrier, and some invade the cells. A better understanding of the cross talk between enterovirulent bacteria and the polarized intestinal cells has resulted in the identification of essential enterovirulent bacterial structures and virulence gene products playing pivotal roles in pathogenesis. Cultured animal cell lines and cultured human nonintestinal, undifferentiated epithelial cells have been extensively used for understanding the mechanisms by which some human enterovirulent bacteria induce intestinal disorders. Human colon carcinoma cell lines which are able to express in culture the functional and structural characteristics of mature enterocytes and goblet cells have been established, mimicking structurally and functionally an intestinal epithelial barrier. Moreover, Caco-2-derived M-like cells have been established, mimicking the bacterial capture property of M cells of Peyer's patches. This review intends to analyze the cellular and molecular mechanisms of pathogenesis of human enterovirulent bacteria observed in infected cultured human colon carcinoma enterocyte-like HT-29 subpopulations, enterocyte-like Caco-2 and clone cells, the colonic T84 cell line, HT-29 mucus-secreting cell subpopulations, and Caco-2-derived M-like cells, including cell association, cell entry, intracellular lifestyle, structural lesions at the brush border, functional lesions in enterocytes and goblet cells, functional and structural lesions at the junctional domain, and host cellular defense responses.

Aflatoxin, fumonisin and Shiga toxin-producing Escherichia coli infections in calves and the effectiveness of Celmanax®/Dairyman's Choice™ applications to eliminate morbidity and mortality losses

Mycotoxin mixtures are associated with Shiga toxin-producing Escherichia coli (STEC) infections in mature cattle. STEC are considered commensal bacteria in mature cattle suggesting that mycotoxins provide a mechanism that converts this bacterium to an opportunistic pathogen. In this study, we assessed the mycotoxin content of hemorrhaged mucosa in dairy calves during natural disease outbreaks, compared the virulence genes of the STECs, evaluated the effect of the mucosal mycotoxins on STEC toxin expression and evaluated a Celmanax^®/Dairyman’s Choice™ application to alleviate disease. As for human infections, the OI-122 encoded nleB gene was common to STEC genotypes eliciting serious disease. Low levels of aflatoxin (1–3 ppb) and fumonisin (50–350 ppb) were detected in the hemorrhaged mucosa. Growth of the STECs with the mycotoxins altered the secreted protein concentration with a corresponding increase in cytotoxicity. Changes in intracellular calcium indicated that the mycotoxins increased enterotoxin and pore-forming toxin activity. A prebiotic/probiotic application eliminated the morbidity and mortality losses associated with the STEC infections. Our study demonstrates: the same STEC disease complex exists for immature and mature cattle; the significance of the OI-122 pathogenicity island to virulence; the significance of mycotoxins to STEC toxin activity; and, finally, provides further evidence that prebiotic/probiotic applications alleviate STEC shedding and mycotoxin/STEC interactions that lead to disease.

Different types of cell death induced by enterotoxins

The infection of bacterial organisms generally causes cell death to facilitate microbial invasion and immune escape, both of which are involved in the pathogenesis of infectious diseases. In addition to the intercellular infectious processes, pathogen-produced/secreted enterotoxins (mostly exotoxins) are the major weapons that kill host cells and cause diseases by inducing different types of cell death, particularly apoptosis and necrosis. Blocking these enterotoxins with synthetic drugs and vaccines is important for treating patients with infectious diseases. Studies of enterotoxin-induced apoptotic and necrotic mechanisms have helped us to create efficient strategies to use against these well-characterized cytopathic toxins. In this article, we review the induction of the different types of cell death from various bacterial enterotoxins, such as staphylococcal enterotoxin B, staphylococcal alpha-toxin, Panton-Valentine leukocidin, alpha-hemolysin of Escherichia coli, Shiga toxins, cytotoxic necrotizing factor 1, heat-labile enterotoxins, and the cholera toxin, Vibrio cholerae. In addition, necrosis caused by pore-forming toxins, apoptotic signaling through cross-talk pathways involving mitochondrial damage, endoplasmic reticulum stress, and lysosomal injury is discussed.

Enterotoxigenic Escherichia coli modulates host intestinal cell membrane asymmetry and metabolic activity

Enterotoxigenic Escherichia coli (ETEC) is a common cause of travelers' and postweaning diarrhea in humans and swine, respectively. The extent to which ETEC damages host cells is unclear. Experiments are presented that probe the ability of porcine ETEC isolates to induce apoptosis and cell death in porcine intestinal epithelial cells. Quantification of host phosphatidylserine exposure following ETEC infection suggested that ETEC induced changes in plasma membrane asymmetry, independent of the expression of the heat-labile enterotoxin. Significant host cell death was not observed. ETEC infection also caused a drastic inhibition of host esterase activity, as measured by calcein fluorescence. While ETEC infection resulted in activation of host caspase 3, terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling of DNA double-strand breakage, indicative of late stages of apoptosis, was not observed. Camptothecin-induced apoptosis markedly increased subsequent ETEC adherence. Transfer of cell-free supernatants from apoptotic cells to bacterial inocula prior to infection of naïve cells increased the transcriptional activity of the regulatory region upstream of the K88ac operon and promoted subsequent adherence to host cells.

Emergence and outbreaks of CTX-M beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae strains in a Tunisian hospital

Sixty-two isolates of Enterobacteriaceae (35 Escherichia coli and 27 Klebsiella pneumoniae isolates) producing CTX-M-type beta-lactamases were collected between March 2000 and June 2003 in different wards of Charles Nicolle Hospital in Tunis (Tunisia). Sequencing identified the bla(CTX-M-15) determinant in 55 isolates and bla(CTX-M-16) in 7 isolates. The CTX-M-15-producing strains were isolated in several wards and consisted mainly of two successive clonal groups of E. coli and a major clonal group of K. pneumoniae. The second clonal group of E. coli belonged to phylogenetic group B2 and harbored more virulence factors than the first clonal group. Among the 22 transconjugants or electroporants obtained with selected E. coli and K. pneumoniae CTX-M-15-producing strains, a predominant plasmid restriction pattern was obtained with 17 isolates. The four CTX-M-16-producing strains of E. coli yielded the same pulsed-field gel electrophoresis (PFGE) pattern, while the three CTX-M-16-producing strains of K. pneumoniae yielded two different PFGE patterns. All of the CTX-M-16-producing isolates were recovered in the pediatric ward and had the same plasmid restriction pattern.

The secreted autotransporter toxin, Sat, functions as a virulence factor in Afa/Dr diffusely adhering Escherichia coli by promoting lesions in tight junction of polarized epithelial cells

Afa/Dr diffusely adhering Escherichia coli (DAEC) strains are responsible for urinary tract and intestinal infections. Both in intestine and kidney, the epithelial cells forming epithelium are sealed by junctional domains. We provide evidence that the Secreted autotransporter toxin, Sat, belonging to the subfamily of serine protease autotransporters of Enterobacteriaceae (SPATEs), acts as a virulence factor in Afa/Dr DAEC by promoting lesions in the tight junctions (TJs) of polarized epithelial Caco-2/TC7 cells. Southern blot analysis reveals that the prototype strains of the subclass-1 and subclass-2 typical Afa/Dr DAEC strains, hybridize with a sat probe. Using the wild-type IH11128 strain, the recombinant E. coli AAEC185 strain that expresses Sat, the recombinant E. coli that expresses both Dr adhesin and Sat, we report that Sat in monolayers of cultured enterocyte-like Caco-2/TC7 cells, induces rearrangements of the TJs-associated proteins ZO-1, ZO-3 and occludin, and increases the formation of domes as the result of an increase in the paracellular permeability without affecting the transepithelial electrical resistance of the cell monolayers. Moreover, we observe that Sat-induced disassembly of TJs-associated proteins is dependent on the serine protease motif. Finally, an analysis of the prevalence of the sat gene in three collections of Afa/Dr DAEC strains collected from the stools of children with and without diarrhoea, and from the urine of patients with urinary tract infection (UTI) shows that: (i) the sat gene is highly prevalent in UTI-associated Afa/Dr DAEC strains (88% positive), (ii) the sat gene is generally absent from Afa/Dr DAEC strains collected from the stools of children without diarrhoea (16% positive); whereas (iii) it is present in about half of the strains collected from the stools of children with diarrhoea (46% positive).

Essential oils--their antimicrobial activity against Escherichia coli and effect on intestinal cell viability

Essential oils are known to possess antimicrobial activity against a wide spectrum of bacteria. The main objective of this study was to evaluate possible harmful effects of four commonly used essential oils and their major components on intestinal cells. Antimicrobial activity of selected plant extracts against enteroinvasive Escherichia coli was dose dependent. However, doses of essential oils with the ability to completely inhibit bacterial growth (0.05%) showed also relatively high cytotoxicity to intestinal-like cells cultured in vitro. Lower doses of essential oils (0.01%) had only partial antimicrobial activity and their damaging effect on Caco-2 cells was only modest. Cell death assessment based on morphological and viability staining followed by fluorescence microscopy showed that essential oils of cinnamon and clove and their major component eugenol had almost no cytotoxic effect at lower doses. Although essential oil of oregano and its component carvacrol slightly increased the incidence of apoptotic cell death, they showed extensive antimicrobial activity even at lower concentrations. Relatively high cytotoxicity was demonstrated by thyme oil, which increased both apoptotic and necrotic cell death incidence. In contrast, its component thymol showed no cytotoxic effect as well as greatly-reduced ability to inhibit visible growth of the chosen pathogen in the doses used. On the other hand, the addition of all essential oils and their components at lower doses, with the exception of thyme oil, to bacterial suspension significantly reduced the cytotoxic effect of E. coli on Caco-2 cells after 1h culture. In conclusion, it is possible to find appropriate doses of essential oils showing both antimicrobial activity and very low detrimental effect on intestinal cells.

Mechanisms of renal damage owing to infection

Urinary tract infection (UTI) is a common bacterial illness in children. It is known to be associated with an increased risk of permanent renal cell damage and scarring which may lead to generation of pathological conditions such as hypertension, pre-eclampsia during pregnancy, renal insufficiency, and end-stage kidney disease. The pathophysiology of renal scarring is still obscure, which makes the prevention of renal damage difficult. During acute infection, there are numerous factors that may contribute to tissue damage. Inflammatory responses are activated by host defense mechanisms as well as by specific bacterial virulence factors. Understanding of these complex mechanisms would be helpful to better identify children at high risk of developing renal scarring following UTI.

E. colivirulence factor hemolysin induces neutrophil apoptosis and necrosis/lysis in vitro and necrosis/lysis and lung injury in a rat pneumonia model

Enteric gram-negative bacilli, such as Escherichia coli are the most common cause of nosocomial pneumonia. In this study a wild-type extraintestinal pathogenic strain of E. coli (ExPEC)(CP9) and isogenic derivatives deficient in hemolysin (Hly) and cytotoxic necrotizing factor (CNF) were assessed in vitro and in a rat model of gram-negative pneumonia to test the hypothesis that these virulence factors induce neutrophil apoptosis and/or necrosis/lysis. As ascertained by in vitro caspase-3/7 and LDH activities and neutrophil morphology, Hly mediated neutrophil apoptosis at lower E. coli titers (1 × 105–6cfu) and necrosis/lysis at higher titers (≥1 × 107cfu). Data suggest that CNF promotes apoptosis but not necrosis or lysis. We also demonstrate that annexin V/7-amino-actinomycin D staining was an unreliable assessment of apoptosis using live E. coli. The use of caspase-3/7 and LDH activities and neutrophil morphology supported the notion that necrosis, not apoptosis, was the primary mechanism by which neutrophils were affected in our in vivo gram-negative pneumonia model using live E. coli. In addition, in vivo studies demonstrated that Hly mediates lung injury. Neutrophil necrosis was not observed when animals were challenged with purified lipopolysaccharide, demonstrating the importance of using live bacteria. These findings establish that Hly contributes to ExPEC virulence by mediating neutrophil toxicity, with necrosis/lysis being the dominant effect of Hly on neutrophils in vivo and by lung injury. Whether Hly-mediated lung injury is due to neutrophil necrosis, a direct effect of Hly, or both is unclear.

Pathogenesis of Afa/Dr diffusely adhering Escherichia coli

Over the last few years, dramatic increases in our knowledge about diffusely adhering Escherichia coli (DAEC) pathogenesis have taken place. The typical class of DAEC includes E. coli strains harboring AfaE-I, AfaE-II, AfaE-III, AfaE-V, Dr, Dr-II, F1845, and NFA-I adhesins (Afa/Dr DAEC); these strains (i) have an identical genetic organization and (ii) allow binding to human decay-accelerating factor (DAF) (Afa/Dr(DAF) subclass) or carcinoembryonic antigen (CEA) (Afa/Dr(CEA) subclass). The atypical class of DAEC includes two subclasses of strains; the atypical subclass 1 includes E. coli strains that express AfaE-VII, AfaE-VIII, AAF-I, AAF-II, and AAF-III adhesins, which (i) have an identical genetic organization and (ii) do not bind to human DAF, and the atypical subclass 2 includes E. coli strains that harbor Afa/Dr adhesins or others adhesins promoting diffuse adhesion, together with pathogenicity islands such as the LEE pathogenicity island (DA-EPEC). In this review, the focus is on Afa/Dr DAEC strains that have been found to be associated with urinary tract infections and with enteric infection. The review aims to provide a broad overview and update of the virulence aspects of these intriguing pathogens. Epidemiological studies, diagnostic techniques, characteristic molecular features of Afa/Dr operons, and the respective role of Afa/Dr adhesins and invasins in pathogenesis are described. Following the recognition of membrane-bound receptors, including type IV collagen, DAF, CEACAM1, CEA, and CEACAM6, by Afa/Dr adhesins, activation of signal transduction pathways leads to structural and functional injuries at brush border and junctional domains and to proinflammatory responses in polarized intestinal cells. In addition, uropathogenic Afa/Dr DAEC strains, following recognition of beta(1) integrin as a receptor, enter epithelial cells by a zipper-like, raft- and microtubule-dependent mechanism. Finally, the presence of other, unknown virulence factors and the way that an Afa/Dr DAEC strain emerges from the human intestinal microbiota as a "silent pathogen" are discussed.

A specific genetic background is required for acquisition and expression of virulence factors in Escherichia coli

In bacteria, the evolution of pathogenicity seems to be the result of the constant arrival of virulence factors (VFs) into the bacterial genome. However, the integration, retention, and/or expression of these factors may be the result of the interaction between the new arriving genes and the bacterial genomic background. To test this hypothesis, a phylogenetic analysis was done on a collection of 98 Escherichia coli/Shigella strains representing the pathogenic and commensal diversity of the species. The distribution of 17 VFs associated to the different E. coli pathovars was superimposed on the phylogenetic tree. Three major types of VFs can be recognized: (1) VFs that arrive and are expressed in different genetic backgrounds (such as VFs associated with the pathovars of mild chronic diarrhea: enteroaggregative, enteropathogenic, and diffusely-adhering E. coli), (2) VFs that arrive in different genetic backgrounds but are preferentially found, associated with a specific pathology, in only one particular background (such as VFs associated with extraintestinal diseases), and (3) VFs that require a particular genetic background for the arrival and expression of their virulence potential (such as VFs associated with pathovars typical of severe acute diarrhea: enterohemorragic, enterotoxigenic, and enteroinvasive E. coli strains). The possibility of a single arrival of VFs by chance, followed by a vertical transmission, was ruled out by comparing the evolutionary histories of some of these VFs to the strain phylogeny. These evidences suggest that important changes in the genome of E. coli have occurred during the diversification of the species, allowing the virulence factors associated with severe acute diarrhea to arrive in the population. Thus, the E. coli genome seems to be formed by an "ancestral" and a "derived" background, each one responsible for the acquisition and expression of different virulence factors.

Prevalence of secreted autotransporter toxin gene among diffusely adheringEscherichia coliisolated from stools of children

In this report, we analyzed the prevalence of the sat gene in 336 Escherichia coli samples collected from stools of children with and without diarrhea in Brazil and in 100 uropathogenic E. coli strains. The results show a high correlation between diffusely adhering E. coli (DAEC) and the presence of sat (44%) in intestinal isolates. DAEC strain FBC114 expresses a 107-kDa protein, which showed 98% homology with Sat.

Uropathogenic Escherichia coli toxins induce caspase-independent apoptosis in renal proximal tubular cells via ERK signaling

BACKGROUND

Pyelonephritis is a risk factor for renal tubular epithelial cell damage. Recent studies have shown that Escherichia coli and/or its toxins may stimulate apoptotic cell death in renal tubular cells, but the underlying molecular mechanisms remain to be elucidated.

METHODS

Confluent LLC-PK(1) cells were exposed to E. coli toxins from overnight cultures of the uropathogenic O6K13H1 (O6) and the nonpathogenic W3110. The cell death was studied with morphological and biological assay.

RESULTS

E. coli soluble toxins from uropathogenic O6:K13:H1(O6) strain were found to induce apoptosis in a dose- and time-dependent manner in LLC-PK1 cells. The expression of FasR and the phosphorylation of ERK1/2 were significantly upregulated by O6 soluble toxins in a time-dependent manner. Cell death was completely inhibited by two specific ERK1/2 inhibitors, but not by a broad caspase inhibitor, zVAD-fmk, implicating a caspase-independent pathway via ERK. Moreover, we found that lysophosphatidic acid could trigger a survival signal through G-proteins and PI3K.

CONCLUSION

We demonstrate that apoptosis induced by uropathogenic E. coli toxins is dependent on ERK1/2. Caspases, although being activated, are not necessary for cell death, and they act after the ERK signaling at which point cells become committed to cell death or can be rescued.

Representational difference analysis between Afa/Dr diffusely adhering Escherichia coli and nonpathogenic E. coli K-12

Diffusely adhering Escherichia coli strains harboring Afa/Dr adhesins (Afa/Dr DAEC) have been associated with diarrhea and urinary tract infections (UTIs). The present work is the first extensive molecular study of a Afa/Dr DAEC strain using the representational difference analysis technique. We have searched for DNA sequences present in strain C1845, recovered from a diarrheagenic child, but absent from a nonpathogenic K-12 strain. Strain C1845 harbors part of a pathogenicity island (PAI(CFT073)) and several iron transport systems found in other E. coli pathovars. We did not find genes encoding factors known to subvert host cell proteins, such as type III secretion system or effector proteins. Several C1845-specific sequences are homologous to putative virulence genes or show no homology with known sequences, and we have analyzed their distribution among Afa/Dr and non-Afa/Dr clinical isolates and among strains from the E. coli Reference Collection. Three C1845-specific sequences (MO30, S109, and S111) have a high prevalence (77 to 80%) among Afa/Dr strains and a low prevalence (12 to 23%) among non-Afa/Dr strains. In addition, our results indicate that strain IH11128, an Afa/Dr DAEC strain recovered from a patient with a UTI, is genetically closely related to strain C1845.

Stereo-isomer specific induction of renal cell apoptosis by synthetic muramyl dipeptide (N-acetylmuramyl-L-alanyl-D-isoglutamine)

The cytotoxicity of bacterial cell wall components, muramyl dipeptide (synthetic N-acetylmuramyl-L-alanyl-D-isoglutamine; L,D-MDP) and lipopolysaccharide (LPS), was investigated in several kidney cell lines. MDP and LPS were toxic to rabbit and monkey kidney cells, MDP was toxic to canine kidney cells, but not to human or porcine kidney cells. Notably, L,D-MDP was >100-fold more cytotoxic/microg than the D,D-MDP and L,L-MDP, as well as LPS. L,D-MDP and analogs containing L,D-MDP were the most widely cytotoxic of the MDP tested. The MDP-induced cytotoxicity was characterized as apoptosis by DAPI staining and DNA laddering. The acute rabbit kidney (RK13) cell apoptosis (cell death in < 5 h) induced by apical or basal application of MDP was associated with glutamate (Glu) release, decreased gamma-glutamyltranspeptidase (GGT) and acidosis and was suppressed by Indomethacin, Naproxen and Curcumin. The cytotoxic activity of L,D-MDP was decreased significantly by 24 h incubation in human sera. Aged (> 2 year-old) rabbits that apparently failed to quickly clear and excrete a uveitogenic dose of MDP within 24 h died in I week. The results indicate that minute amounts (5 ng/ml) of MDP containing L-alanyl-D-isoglutamine can induce renal cell apoptosis in vitro and support MDP-induced kidney cytotoxicity in rabbits. Also, the results indicate that MDP in sera can be detected utilizing the RK13 cell bioassay and that failure to rapidly clear and excrete L,D-MDP is associated with uveitis and death in aged rabbits.

Glycosylphosphatidylinositol-anchored receptor-mediated bacterial endocytosis

An increasing number of pathogens or their toxins appear to utilize glycosylphosphatidylinositol(GPI)-anchored receptors to trigger entry into immune and other host cells. Since these receptors have no transmembrane and intracellular moieties, how endocytosis is initiated is unclear. Recently, CD48 on mast cell membranes was shown to trigger endocytosis of bacteria via a route that avoids fusion with lysosomes and by a mechanism involving discrete cellular entities called caveolae. The localization of CD48 within caveolae appears to be a prerequisite for caveolae-mediated bacterial entry.