Rickettsial stimulation of endothelial platelet-activating factor synthesis

Endothelial cells (EC) synthesize platelet-activating factor (PAF) when activated by agents such as ATP or thrombin, and PAF production occurs as a consequence of endothelial phospholipase A activity. Because interactions between Rickettsia prowazekii and a variety of host cells result in the expression of phospholipase A activity, we assessed the relative abilities of uninfected and rickettsia-infected EC to synthesize PAF. Endothelial cells were infected with rickettsiae and examined at 24-h intervals for rickettsial multiplication, EC viability, and PAF synthesis. By 24 h postinfection, 80% of the EC were infected with an average of 10.6 rickettsiae per cell; by 72 h, the rickettsiae were too numerous to count and the numbers of viable EC began to decrease. Both rickettsia-infected and sham-treated EC synthesized PAF when stimulated with either thrombin or ATP, but rickettsia-infected EC synthesized about three times as much PAF in response to cell activation as did their uninfected counterparts. Additionally, unlike their uninfected counterparts, rickettsia-infected EC synthesized significant amounts of PAF in the absence of cell activation; rickettsia-infected EC synthesized as much PAF in the absence of activation as did uninfected EC in response to ATP. In each case, essentially all of the newly synthesized PAF remained with the cell pellet. Finally, EC incubated with high numbers of rickettsiae (1,000 rickettsiae per EC) for 30 min synthesized more PAF when activated with ATP than did their sham-treated activated counterparts.

Serologic characterization of Rocky Mountain spotted fever. Appearance of antibodies reactive with endothelial cells and phospholipids, and factors that alter protein C activation and prostacyclin secretion

Rocky Mountain spotted fever (RMSF) takes its name from the characteristic rash that occurs as a consequence of vasculitis associated with rickettsial invasion of the endothelium. The authors examined sera from 14 patients with serologically confirmed RMSF for the presence of antibodies (IgG and IgM) reactive with human umbilical vein-derived endothelial cells and with the phospholipids cardiolipin (CL) and phosphatidyl serine (PS). Sera from 7 patients (50%) exhibited antiendothelial antibodies, and 10 (71%) patient sera reacted with CL and/or PS. Because such antibodies may interfere with or augment endothelial thrombosis-related activities, acute and convalescent sera were tested for their effects on endothelial PGI2 secretion and protein C activation. Acute sera from two patients and convalescent sera from four patients stimulated protein C activation. Additionally, sera from five acute and nine convalescent cases inhibited basal endothelial PGI2 secretion, but sera from two acute and three convalescent cases stimulated thrombin-dependent PGI2 secretion. These results demonstrated that, in a significant proportion of patients, RMSF was accompanied by the appearance of antibodies that bound to endothelial cells and to phospholipids; some of these antibodies may have altered anticoagulant endothelial functions.

Effects of typhus rickettsiae on peritoneal and alveolar macrophages: rickettsiae stimulate leukotriene and prostaglandin secretion

Monolayers of mouse resident peritoneal macrophages were incubated with typhus rickettsiae, and macrophage secretion of leukotriene B4 (LTB4) was assessed. Macrophages incubated with native rickettsiae, but not those incubated with hemolytically inactivated rickettsiae, secreted significantly more LTB4 than did sham-treated macrophages. Antirickettsial antiserum was opsonic and blocked hemolysis, and macrophages incubated with rickettsiae in the presence of antiserum did not secrete more LTB4 than those incubated with buffer alone. Native rickettsiae also stimulated alveolar macrophages to secrete LTB4 and prostaglandin E2 (PGE2), but inactivated rickettsiae had no effect. Finally, because trifluoperazine did not alter macrophage LTB4 secretion in the presence of rickettsiae, but inhibited PGE2 secretion, it was suggested that the mechanisms by which rickettsiae stimulated production of these autacoids may have differed.

Rickettsial effects on leukotriene and prostaglandin secretion by mouse polymorphonuclear leukocytes

Typhus rickettsiae were incubated with mouse exudative polymorphonuclear leukocytes (PMN), and supernatants were examined for leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) secretion by radioimmunoassay. PMN incubated with native rickettsiae secreted significantly more LTB4 and PGE2 than did those incubated with buffer alone. Autacoid secretion was dependent on both the time of PMN incubation with rickettsiae and the number of rickettsiae present in the incubation suspension. Rickettsial stimulation of LTB4 secretion was associated with rickettsial hemolytic activity; treatments which inactivated the rickettsial hemolysin abolished the ability of rickettsiae to stimulate PMN LTB4 secretion. Trifluoperazine, which did not alter the rate of phagocytosis of rickettsiae by PMN, stimulated rickettsial effects on secretion of both LTB4 and PGE2 but inhibited the PMN LTB4 response to A23187. This suggested that the PMN response to rickettsiae and to the calcium ionophore involved differing mechanisms of activation. Finally, rabbit antirickettsial antiserum, which inhibited rickettsial hemolysis and was opsonic, did not block the effects of rickettsiae on PMN LTB4 secretion.

Endothelial prostaglandin secretion: effects of typhus rickettsiae

Cultured human umbilical vein-derived endothelial cells were incubated with typhus rickettsiae, and supernatants were examined for the presence of prostaglandins I2 (PGI2) and E2 (PGE2). Cells incubated with metabolically active rickettsiae secreted significantly more PGI2 and PGE2 than did those incubated with buffer alone or with killed rickettsiae. The amount of PGI2 secreted was directly related to the number of hemolytically active rickettsiae present; abolishing rickettsial hemolytic activity abolished their effect on PGI2 secretion. Mice injected with a lethal dose of native typhus rickettsiae exhibited a rapid rise in circulating PGI2 levels; mice given hemolytically inactive rickettsiae survived and exhibited no rise in plasma PGI2 levels. Finally, endothelial cells were infected with rickettsiae, and secretion of prostaglandins was monitored during rickettsial multiplication; intracellular accumulation of rickettsiae resulted in endothelial destruction and a dramatic increase in endothelial secretion of PGI2 and PGE2. Therefore, typhus rickettsiae can increase endothelial secretion of arachidonate-derived autocoids.

Evaluation of lupus anticoagulants: antiphospholipid antibodies, endothelium associated immunoglobulin, endothelial prostacyclin secretion, and antigenic protein S levels

Plasma samples from nineteen patients with well characterized lupus anticoagulants (LA) were evaluated using a series of test systems. An ELISA was used to determine if the plasmas contained antiphospholipid antibodies (APA); fifteen of nineteen LA plasmas contained APA, with five exhibiting IgG only, two exhibiting IgM, and eight plasmas containing both IgG and IgM. Anti-phosphatidyl serine (PS) was the predominant IgG specificity and all IgM APA-containing plasmas reacted with phosphatidyl inositol (PI). An ELISA was developed to determine if LA plasmas contained immunoglobulin which would associate with cultured human umbilical cord vein-derived endothelial cells (HUV); ten of nineteen plasmas contained endothelium associated immunoglobulin (EAI). There was significant concordance between the occurrence of EAI and IgM anti-PI. The occurrence of EAI or APA, either singly or in combination, did not correlate with a past history of thrombosis. Patient plasmas were incubated with HUV and examined for effects on HUV prostacyclin (PGI2) secretion; six plasmas significantly stimulated PGI2 secretion and one plasma was inhibitory. Finally, plasma levels of free and total antigenic protein S were determined by EID. Five plasmas contained significantly reduced levels of free antigenic protein S, and total antigenic protein S was reduced in ten plasmas. Patient histories were examined for evidence of thrombotic episodes; six patients had a history of either arterial or venous thrombosis, with five of these six patients having drug-induced LA. Thus, unlike previous studies, drug-induced LA were associated with thrombosis.

Rickettsial interactions with human endothelial cells in vitro: adherence and entry

Rickettsia prowazekii, Madrid E strain, was assessed for its ability to enter endothelial cells derived from the veins of human umbilical cord in vitro. Rickettsial entry increased linearly with multiplicity of infection up to a multiplicity of 500; thereafter, additional rickettsiae adhered, but without a concomitant increase in the number of intracellular rickettsiae. Rickettsial entry required participation both of rickettsiae and endothelial cells; inactivation of rickettsiae with N-ethylmaleimide or Formalin, or of endothelial cells with cytochalasin B or D or NaF greatly reduced rickettsial entry. Because rickettsiae adhered to inactivated endothelial cells, adherence could be examined in the absence of entry. Rickettsial adherence was inhibited by poisons that inhibited rickettsial hemolysis. Calcium ionophore A23187, which did not inhibit endothelial pinocytosis, stimulated rickettsial adherence to endothelial cells, but inhibited rickettsial entry. These results indicated that typhus rickettsiae entered endothelial cells via induced phagocytosis, and that the signal for entry, which was dependent upon rickettsial energy, probably involved formation of a calcium gradient.

Comparative studies on the pattern of infection with Giardia spp. in mongolian gerbils

Mongolian gerbils (Meriones unguiculatus) were inoculated with known numbers of Giardia cysts isolated from humans, beavers and mice. The pattern of cyst release in the feces was studied for a period of 35 days. After a latent period of 5 days, animals infected with G. muris release cysts in their feces every day until day 14. Gerbils infected with human or beaver isolates released cysts in their feces intermittently for 30 days. These results indicated that the mode of cyst release in these animals was characteristic of the parasite, and was independent of the host. Mongolian gerbils acquire complete resistance upon homologous species challenge but demonstrate only partial protection when challenged with a different species of Giardia. We concluded that the Mongolian gerbil model could be useful in epidemiological studies for two reasons: it can be used for determination of cyst viability, and for the identification of the etiological agent.

Bartonella bacilliformis: colonial types and erythrocyte adherence

Bartonella bacilliformis was cultivated on a solid medium, and two bartonella colonial morphologies were differentiated and designated colony types T1 and T2. Although both T1 and T2 bartonellae adhered to human erythrocytes in vitro, approximately twice as many T2 bartonellae adhered as did T1. Maximum adherence required bartonella energy, most likely proton motive force-dependent motility. Bartonellae did not penetrate or lyse erythrocytes in vitro. Bartonellae adhered poorly to alpha- or beta-glucosidase-treated erythrocytes, but pronase or subtilisin treatment of erythrocytes stimulated adherence. This indicates that bartonellae probably adhere to an erythrocyte glycolipid moiety.

Interactions between Rickettsia prowazekii and rabbit polymorphonuclear leukocytes: rickettsiacidal and leukotoxic activities

Rickettsia prowazekii was assessed for in vitro susceptibility to phagocytosis by rabbit polymorphonuclear leukocytes. [alpha-32P]adenosine triphosphate-labeled rickettsiae were used to determine phagocytosis and adsorption quantitatively. R. prowazekii was less susceptible to phagocytosis than were Escherichia coli and Neisseria gonorrhoeae. Although R. prowazekii was similar to E. coli in susceptibility to superoxide and activated halide, few phagocytized rickettsial cells were inactivated after being ingested by polymorphonuclear leukocytes, and rickettsiae were observed free in polymorphonuclear leukocyte cytoplasm. At low ratios of rickettsiae to polymorphonuclear leukocytes, PMN phagocytosis increased as a linear function of time, but at high ratios (multiplicity of infection, 50) rickettsiae were phagocytized during only the first 10 min of incubation. Polymorphonuclear leukocytes were damaged in the presence of high rickettsial multiplicities such that they released lactate dehydrogenase into the medium and lost the ability to phagocytize both rickettsiae and E. coli. The amount of leukotoxic activity in a given rickettsial sample correlated with the relative hemolytic activity of that sample. The rickettsial leukotoxin was probably not a soluble product, was active in the absence of phagocytosis, and was inhibited by inactivation of the rickettsiae or by incubation at 4 degrees C.

Rickettsial hemolysis: rapid method for enumeration of metabolically active typhus rickettsiae

A new assay is described for enumerating biologically active typhus rickettsiae (Madrid E strain), based on adsorption of rickettsiae to erythrocytes in the presence of NaF (which allows adsorption but not lysis) and lysis in the presence of anti-Rickettsia prowazeki immune serum (which allows only a single round of lysis). The number of lysed erythrocytes is then used to estimate the number of active rickettsiae.

Penetration of cultured mouse fibroblasts (L cells) by Rickettsia prowazeki

The association of Rickettsia prowazeki with L cells was examined by using a novel radioactive assay in which [alpha-(32)P]ATP-labeled rickettsiae were incubated with L-cell monolayers. Rickettsial association with the monolayer involved adherence and internalization steps that could be experimentally distinguished. Since R. prowazeki but not L cells possess an ATP-ADP obligate exchange transport system, addition of excess unlabeled ATP resulted in exchange of the labeled ATP from external, adherent rickettsiae but not from internalized rickettsiae. Rickettsial association was temperature dependent and was a linear function of both time and concentration. More than 90% of the biologically active rickettsiae associated with L cells was internalized. Rickettsial internalization required active participation of both rickettsiae and L cells; inactivation of either greatly reduced internalization. Rickettsial adherence to poisoned L cells was a saturable function of time and concentration. Adherence showed less temperature dependence than did internalization, but like rickettsial internalization, the extent of adherence was extremely low at 0 degrees C. The rate and extent of adherence by inactivated and native rickettsiae to inactivated L cells were similar. Although inactive rickettsiae adhered to active and inactive L cells to a similar extent, inactive rickettsiae were internalized poorly by active L cells. These data form the basis for the hypothesis that R. prowazeki are internalized by the host cell through a process of "induced phagocytosis" and that inactivated rickettsiae adhere to the host cell differently from native rickettsiae, failing to trigger the endocytosis mechanism.

Plasmid DNA in virulent and avirulent gonococci

The presence of covalently closed circular (CCC) DNA in virulent and avirulent colonial types of Neisseria gonorrhoeae strain 2686, and of type 3 colonies of strain F62 was investigated. CCC DNA was present in each, and the percentage of plasmid relative to total DNA was similar. The percentage of CCC DNA was similar in cells grown on a solid as compared with a liquid medium and in cells grown in the presence of varying concentrations of glucose. No correlation could be established between the presence of plasmid DNA and virulence of N. gonorrhoeae.

Studies on phytochrome. Two photoreversible chromoproteins from etiolated oat seedlings

1. The photoreversible chromoprotein phytochrome was extracted from etiolated oat seedlings. The final purification step revealed that there were two photoreversible coloured components. 2. The amino acid composition, spectra and Svedberg coefficients of each component are reported.

Studies on phytochrome. Some properties of electrophoretically pure phytochrome

1. Phytochrome was purified from etiolated oat (Avena sativa) seedlings either by gel-filtration chromatography and ion-exchange chromatography or by gel-filtration chromatography and calcium phosphate chromatography. Differences were observed in the spectral properties of phytochrome isolated by the two methods. 2. Electrophoresis of pure phytochrome at pH values between 9.0 and 6.0 showed the tendency of phytochrome to form different molecular species. Studies in the ultracentrifuge did not show a corresponding change in the sedimentation coefficient with the change in pH. 3. Tryptic digestion of electrophoretically pure phytochrome gave 17 peptides and a photoactive core. The amino acid composition of the core is reported and compared with the analysis of whole phytochrome. 4. Some properties of phytochrome isolated from Pisum sativum are compared with those of phytochrome from A. sativa. 5. The properties of phytochrome purified by other workers are compared with our findings.