Mediterranean spotted fever due to infection by Rickettsia conorii, is characterized by a general vasculitis. This vasculitis is thought to be due to a direct injury to endothelial cells induced by R. conoryi However, production and activity of cytokines on endothelial cells is an important pathway in inflammation, and part of the underlying mechanism of vasculitis. In the present studies, human umbilical vein endothelial cells (HUVEC) infected with R. conorii actively secrete high levels of IL-8 and IL-6 (P < 0.002, and P < 0.03, respectively, compared with uninfected cells). IL-la, IL1j3, or TNFa were not detected in the culture supernates.Nevertheless, IL-6 and IL-8 production was due, in a large part, to a cell-associated form of IL-la expressed on R. conorii-infected HUVEC, since production of these cytokines was suppressed by 80% (P = 0.0001) and 85% (P < 0.04) by the addition of IL-1 receptor antagonist, or anti-IL-la antibodies (60% inhibition, P < 0.01 and 65% inhibition, P < 0.05, respectively) and IL-la was measured after lysis of R. conorii-infected HUVEC but not in uninfected cells (P < 0.01). Rickettsial lipopolysaccharide does not seem to be involved, since polymyxin B did not reduce cytokine secretion. On the contrary, infection by intracellular R. conorii appears to be necessary to induce IL-la and subsequently IL-8, since formalin-fixed R. conorii did not induce cytokine production. These observations demonstrate that R. conorii-infected HUVEC secrete IL-6 and IL-8 via the induction of cell-associated IL-la, providing a possible mechanism for the vasculitis observed in Mediterranean spotted fever. (J. Clin. Invest. 1995Invest. . 96:2839Invest. -2844

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One-hundred serum samples from 41 patients suffering from Mediterranean spotted fever (MSF) were tested by microimmunofluorescence (MIF) and Western blot (WB; immunoblot). Immunoglobulin G (IgG), IgM, and IgA antibody-specific responses to the high-molecular-mass species-specific protein antigens (115 kDa and 135 kDa) of Rickettsia conorii, as well as to cross-reactive lipopolysaccharide (LPS) antigens, were observed. The WB assay detected IgM-type antibodies earlier than did the MIF assay. These antibodies were often directed against nonspecific LPS and may have a questionable positive predictive value. In addition, an IgG reaction to a 60-kDa protein was observed in four cases of malignant forms of MSF but was never observed in cases of mild forms. This reaction could be correlated with a marker of the severity of the development of MSF. From a previous MIF survey of blood donors, 9 negative, 11 IgG-positive, and 6 IgM-positive serum samples were selected for comparison by WB. Sera negative by MIF were also negative by WB. MIF IgG-positive sera showed a specific response to R. conorii in the WB assay, but the six serum samples from this seroepidemiological study positive for IgM by MIF were almost all negative by the WB assay. One was positive for IgM against the LPS but was considered a false positive. The WB is shown to provide a new tool for serodiagnosis.

Leukocyte adherence to the endothelium is an essential component of the inflammatory response during rickettsial infection. In vitro, Rickettsia conorii infection of endothelial cells enhances the expression of adhesive molecules E-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) in a time- and dose-dependent manner. Rickettsial lipopolysaccharide does not seem to be involved, because polymyxin B does not reduce their expression. The intracellular presence of the organism and de novo host protein synthesis are required for expression of cell adhesive molecules, since rickettsial inactivation by formol and pretreatment of cells with cycloheximide inhibits an increase in expression. The contribution of interleukin-1alpha (IL-1alpha) to this endothelial adhesive phenotype was shown by inhibitory experiments 8 and 24 h after infection with IL-1 receptor antagonist and IL-1alpha blocking antibodies. Enhanced adherence of mononuclear cells to infected endothelial cells involved VCAM-1- and ICAM-1-dependent mechanisms at the late phase of the inflammatory response. This endothelial adhesive phenotype may constitute a key pathophysiologic mechanism in R. conorii-induced vascular injury.

The entry of rickettsiae into eukaryotic cells is mediated by an induced phagocytosis, but rickettsiae have never been observed in a closed phagocytic vacuole. In this study, Rickettsia conorii entry into Vero cells was observed by transmission electron microscopy during a period of 3 to 20 min after bacterium-cell contact. The entry occurred within 3 min after bacterium-cell contact, and R. conorii was observed in the process of engulfment, within a phagocytic vacuole, or free in the cytosol. Escape from the phagosome is a very rapid step since phagosome lysis was only occasionally observed. By 12 min, 90% of bacteria were internalized and half were free in the cytosol. This report confirms that rickettsiae penetrate nonphagocytic cells by induced phagocytosis and is the first demonstration of rickettsiae within a complete phagocytic vacuole.

A case-control study of three cases of Legionella pneumophila pneumonia identified transesophageal echocardiography (TEE) as a risk factor. Patient isolates and environmental strains from water used for rinsing TEE probes were identical by pulsed-field gel electrophoresis. This is the first report of endoscopy as a potential source of legionellosis.

Mediterranean spotted fever, a tick-borne rickettsiosis caused by Rickettsia conorii, may lead to small-vessel or deep-vein thrombosis. In order to evaluate the role of endothelial cell alteration in this lesion, we infected human endothelial cells derived from umbilical veins with R. conorii. We report the induction of two previously unreported prothrombotic mechanisms in rickettsial disease: (i) a progressive decline in thrombomodulin antigen and (ii) early expression of tissue factor, and, as described for R. rickettsii infection, later release of von Willebrand factor from Weibel-Palade bodies. Thrombomodulin expression in infected endothelial cells, measured by the thrombin-dependent activation of protein C or flow cytometric analysis, decreased steadily between 4 and 24 h after inoculation with rickettsiae. R. conorii infection induced tissue factor expression, measured by clotting assay and flow cytometric analysis, which was detectable 2 h postinoculation, reached its maximum 4 h postinoculation, and progressively decreased thereafter. Infection resulted in a relatively late release ofvon Willebrand factor antigen into the culture medium. A double-label immunofluorescence assay for the simultaneous evaluation of von Willebrand factor and R. conorii showed that the depletion of cytoplasmic von Willebrand factor stored in Weibel-Palade bodies was due to a direct effect of the intracellular R. conorii. These disturbances of endothelial function observed with R. conorii-infected cells may provide a paradigm for the elucidation of thrombotic pathobiology with Mediterranean spotted fever.

Eikenella corrodens, a slowly growing gram-negative bacillus that is a normal inhabitant of dental plaque, has been recognized as an infrequent cause of invasive disease. To date, only one case of pancreatic abscess due to E. corrodens in association with other bacteria from the oropharynx has been described. We report herein two cases of pancreatic abscess due to E. corrodens. In one case E. corrodens and Escherichia coli were found in the abscess specimens; in the other case no other pathogen was associated with E. corrodens. In addition, we review descriptions from the literature of abdominal infections caused by E. corrodens.