Rickettsia conorii infection stimulates the expression of ISG15 and ISG15 protease UBP43 in human microvascular endothelial cells.

Rickettsia conorii, an obligate intracellular bacterium and the causative agent of Mediterranean spotted fever, preferentially infects microvascular endothelial cells of the mammalian hosts leading to onset of innate immune responses, characterized by the activation of intracellular signaling mechanisms, release of pro-inflammatory cytokines and chemokines, and killing of intracellular rickettsiae. Our recent studies have shown that interferon (IFN)-ß, a cytokine traditionally considered to be involved in antiviral immunity, plays an important role in the autocrine/paracrine regulation of host defense mechanisms and control of R. conorii growth in the host endothelial cells. Here, we show that R. conorii infection induces the expression of ISG15 (an interferon-stimulated gene coding a protein of 17kD) and UBP43 (an ISG15-specific protease) at the levels of mRNA and protein and report the evidence of ISGylation of as yet unidentified target proteins in cultured human microvascular endothelium. Infection-induced expression of ISG15 and UBP43 requires intracellular replication of rickettsiae and production of IFN-ß, because treatment with tetracycline and presence of an antibody capable of neutralizing IFN-ß activity resulted in near complete attenuation of both responses. Inhibition of R. conorii-induced ISG15 by RNA interference results in significant increase in the extent of rickettsial replication, whereas UBP43 knockdown yields a reciprocal inhibitory effect. In tandem, these results demonstrate the stimulation of interferon-ß-mediated innate immune mechanisms capable of perturbing the growth and replication of pathogenic rickettsiae and provide first evidence for ISG15-mediated post-translational modification of host cellular proteins during infection with an intracellular bacterium.

Selective modulation of antioxidant enzyme activities in host tissues during Rickettsia conorii infection.

The involvement of oxidative mechanisms in the pathogenesis of rickettsiosis was investigated using infection of C3H/HeN mice with sub-lethal and lethal infectious doses of Rickettsia conorii, the causative agent of Mediterranean spotted fever. Microscopic examination of tissues at 48 and 96 h post-infection revealed characteristic pathologic features and the presence of rickettsiae in the endothelium of infected tissues. Activities of key antioxidant enzymes, namely glutathione peroxidase, glutathione reductase, glucose-6-phosphate dehydrogenase, and superoxide dismutase, at these times exhibited a pattern of differential and selective modulation in brain, lungs, and testes of mice infected with viable organisms, whereas heat-inactivated or sonically disrupted rickettsiae had no effect. Of these, most significant changes were evident in the lungs of infected animals. Adaptive alterations in oxidant-scavenging enzymes occurred in apparent correlation with the dose and duration of infection. Treatment with an antioxidant, alpha-lipoic acid, protected against infection-induced oxidative injury via regulation of antioxidant enzyme activities and maintenance of reduced glutathione levels. These results suggest the involvement of regulatory enzymes of glutathione redox and superoxide scavenging systems in the antioxidant response during in vivo infection, the extent of which varies with the titer of viable rickettsiae in different organs of the host.

[Changes in plasma lipoproteins in Mediterranean boutonneuse fever]. / Modifications des lipoprotéines plasmatiques au cours de la fièvre boutonneuse méditerranéenne.

We report 25 cases of boutonneuse fever with, in the acute phase, an increase of plasma transaminases, triglycerides and apoprotein B levels, a decrease of total, HDL and LDL cholesterol and a decrease of apoprotein A. These changes disappeared 1 to 4 weeks after the beginning of treatment. They might be due to a reduced activity of lecithin-cholesterol acetyltransferase and lipoprotein lipase, probably caused by the hepatic and vascular disorders frequently found in this disease.

[Enzymatic parameters in boutonneuse fever. II. Behavior and significance of lactic dehydrogenase]. / Studio di alcuni parametri enzimatici in corso di febbre bottonosa. II-Comportamento e significato della latticodeidrogenasi.

Serum levels of Lactic dehydrogenase (LDH) were determined at weekly intervals, in 52 patients with Boutonneuse Fever: 33 adults (23 uncomplicated and 10 complicated cases) and 19 children (no complication occurred in these patients). In the first week of illness, LDH was increased in 86 and 100% of adults (uncomplicated and complicated cases respectively) and in 89% of children. Mean values were 419 and 472 U/l for adults (uncomplicated and complicated) and 423 for children (normal values until 240 U/l). In total (adults plus children), in the first week, pathological findings were observed in 90% of patients. In the second week, LDH was increased in 53 and 100% for adults, and 66% for children. Mean values were 252 and 306 for adults, and 291 U/l for children. The significance of this increase is related to the pathophysiology of rickettsial diseases. Rickettsiae cause endothelial injury with platelet aggregation, activation of inflammation as well as coagulation mechanisms and subsequently damage of various organ systems at various degree (from silent to evident forms). From a general point of view LDH increase appears in part of platelet origin, at first stage of illness, in part from other organ systems involved in the vasculitic process.

[Hepatic involvement in boutonneuse fever (author's transl)]. / La afección hepática en la fiebre botonosa.

Boutonneuse fever is a rickettsioses which is endemic in the Mediterranean countries. Since 1972 we have had the chance to study eight observations os this disease (6 in the last year) and our attention has been drawn by the constant hepatic involvement. This was biological in all cases and histopathologic in the five patients submitted to a liver biopsy. Functional liver tests showed an elevation of SGOT and SGPT in six patients, as well as of the alkaline phosphatase and/or gamma-GT in five. No signs of hepatocellular insufficiency were detected and posterior controls demonstrated a complete normalization of the analytical parameters. As regards the histopathologic findings the most important was the fibrous enlargement of the porta spaces with slight infiltration by round cells, hyperplasia of the Kupffer's cells, and accumulations of histiocytes and lymphocytes. In no patient did we observed epithelioid granulomas. The authors conclude that the hepatic involvement in boutonneuse fever is benign but very constant, which means that it ought to be known about and that it has no defined histopathologic patterns.

The liver in boutonneuse fever.

Hepatic lesions were studied for the first time in 13 cases of boutonneuse fever (Mediterranean exanthematous fever). The glutamic-oxalacetic transaminases were raised in eight patients, the glutamic-pyruvic transaminases showed an increase in 10 patients, alkaline phosphatases in seven of the 10 patients investigated, and conjugate bilirubin showed moderate increases in three patients. Five patients were studied histologically; this study showed lesions of a granulomatous type, similar to those described in Q fever, in three patients, fatty degeneration with marked alcoholism in another patient, and a normal liver in the last patient. Two of the three patients with granulomatous lesions showed a moderate increase in alkaline phosphatases. After this report boutonneuse fever must be included among the infectious conditions that can produce granulomas within the liver.