lipid-a and Typhoid-Fever

Modification of a lipid A moiety in Gram-negative bacterial LPS to a less acylated form is thought to facilitate bacterial evasion of host innate immunity, thereby enhancing pathogenicity. The contribution of less-acylated lipid A to interactions of whole bacterial cells with host cells (especially in humans) remains unclear. Mutant strains of Salmonella enterica serovar Typhimurium with fewer acylated groups were generated. The major lipid A form in wild-type (WT) and the mutant KCS237 strain is hexa-acylated; in mutant strains KCS311 and KCS324 it is penta-acylated; and in KCS369 it is tetra-acylated. WT and KCS237 formalin-killed and live bacteria, as well as their LPS, strongly stimulated production of pro-inflammatory cytokines in human U937 cells; this stimulation was suppressed by TLR4 suppressors. LPS of other mutants produced no agonistic activity, but strong antagonistic activity, while their formalin-killed and live bacteria preparations had weak agonistic and no antagonistic activity. Moreover, these less-acylated mutants had increased resistance to phagocytosis by U937 cells. Our results indicate that a decrease of one acyl group (from six to five) is enough to allow Salmonella to evade human innate immunity and that the antagonistic activity of less-acylated lipid A is not utilized for this evasion.

Topics: Acetylation; Antibodies, Blocking; Cytokines; Humans; Immune Evasion; Immunity, Innate; Inflammation Mediators; Lipid A; Macrophage Activation; Macrophages; Mutation; Salmonella typhi; Toll-Like Receptor 4; Typhoid Fever; U937 Cells

Humoral and cellular immune responses to Salmonella typhi have been studied in nine children with typhoid fever. By using dot immunobinding assay, anti-O-polysaccharide chain and antilipid A antibody titers have been evaluated during the course of the disease. Anti-O-polysaccharide chain antibody titers are lower at the first week and increase up to the third week of the infection. On the other hand, antilipid A antibody levels, which are already higher at the beginning of the disease, progressively augment during the following weeks. Concerning cellular immunity to S. typhi, antibacterial activity mediated by typhoid peripheral mononuclear cells has been determined. Results show this function to be depressed in the initial phase of typhoid, increasing with the time. Together, these data bring new insight on immunity in typhoid patients.

Topics: Antibodies, Bacterial; Antibody-Dependent Cell Cytotoxicity; Child; Child, Preschool; Female; Humans; Immunity, Cellular; Leukocytes, Mononuclear; Lipid A; Male; Polysaccharides, Bacterial; Salmonella typhi; Typhoid Fever

The ability of blood sera obtained from healthy persons and typhoid patients to induce agglutination of red blood cells sensitized with chemotype Re glycolipid has been studied. The blood sera of healthy persons have been shown to possess low endotoxin-binding activity (the reciprocal titer amounts to 21.6 +/- 3.7). In typhoid patients with a severe clinical course of the disease the titers are slightly elevated (49.8 +/- 12.8), in patients with a moderate course a sharp elevation of the titers is observed (240.3 +/-32.8), and in chronic carriers the titers are at a medium level (119 +/- 24.7). The highest titers (288 +/- 72.2) were observed during the first 2 weeks in a moderately severe course of the disease, and by the end of the disease these titers dropped (143.1 +/0 27.4). The endotoxin-binding activity of the sera was inhibited by glycolipid Re and dextran sulfate. The activity of the sera decreased after treatment with 2-mercaptoethanol. The conclusion on a protective role played by antibodies to glycolipid Re and by proteins binding glycolipid and other polyanions has been made on the basis of the data obtained in this study.

Topics: Animals; Antibodies, Bacterial; Carrier State; Endotoxins; Erythrocyte Aggregation; Glycolipids; Hemagglutination Tests; Humans; Lipid A; Rabbits; Typhoid Fever

Present laboratory tests for human typhoid vaccines use an intraperitoneal route of challenge given 7 days after injection of increasing doses of standard and test vaccines by the same route. In studies reported here, groups of B6D2 mice were vaccinated intraperitoneally with 2 x 10(8) acetone-killed Salmonella typhi Ty2, with the Vi antigen-free variant O-901, or with Yersinia enterocolitica and Serratia marcescens suspensions. Other groups of mice received 200 mug of purified S. typhi or S. marcescens endotoxin, or their corresponding purified lipid A components. All of the vaccinated mice (except for saline- or thioglycolate-injected controls) exhibited increased protection against the lethal intraperitoneal challenge with S. typhi Ty2. Serial quantitative bacterial counts carried out on peritoneal washouts and on homogenates of the draining mediastinal lymph nodes indicated the development of an antibacterial response by the vaccinated host which was not observed in the control animals. Mice receiving purified endotoxin (lipopolysaccharide) exhibited varying degrees of protection, both in terms of increased host survival and the amount of inactivation of the challenge population in vivo. The response seen when the antigenically unrelated S. marcescens lipopolysaccharide was injected was little different from that seen when the acetone-killed S. typhi Ty2 whole-cell vaccine was used. This suggests that nonspecific inactivation of the intraperitoneal challenge contributes substantially to the immune response seen in mice vaccinated intraperitoneally with specific typhoid antigens.

Topics: Animals; Humans; Immunization; Injections, Intraperitoneal; Injections, Intravenous; Lipid A; Mice; Mice, Inbred C57BL; Mice, Inbred DBA; Salmonella typhi; Serratia marcescens; Time Factors; Typhoid Fever; Typhoid-Paratyphoid Vaccines; Yersinia