A heat-stable component of Bartonella henselae upregulates intercellular adhesion molecule-1 expression on vascular endothelial cells.

Bartonella henselae upregulated the expression of intercellular adhesion molecule-1 (ICAM-1) on human umbilical vein endothelial cells (HUVECs). The induction level of ICAM-1 depended on the inoculation bacterial dose. ICAM-1 expression began increasing 4 h after infection and reached a sustained peak beginning at 12 h after B. henselae infection; this time course was similar to that of lipopolysaccharide (LPS) of Escherichia coli. The stimulatory effect was abolished when live B. henselae were separated from HUVECs by a filter membrane. The nonpiliated strain, which is unable to invade endothelial cells, induced ICAM-1 expression to the same extent as the piliated strain. Inactivation of B. henselae by ultraviolet (UV) irradiation, heat (56 degrees C, 30 min), or sonication did not alter its stimulatory activity. Polymyxin B, which strongly inhibited the effect of LPS, did not exert any influence on the stimulatory activity of B. henselae. Furthermore, the effect of sonicated B. henselae was not inhibited even by boiling, which was also the case with LPS. Our data suggest that some heat-stable component of B. henselae binds to the endothelial cell surface, inducing ICAM-1 expression. Though the participation of LPS could not be completely ruled out, we suppose that some unidentified heat-stable proteins, lipids, or polysaccharides may be the stimulatory factor(s). The ability of B. henselae to enhance the expression of adhesion molecules on endothelial cells may be an important mechanism in the pathogenesis of B. henselae infection.

Live Bartonella henselae enhances endothelial cell proliferation without direct contact.

The proliferation of human umbilical vein endothelial cells (HUVECs) cocultivated with live B. henselae was enhanced in a bacterial dose-dependent manner, and the stimulatory effect was specific to vascular endothelial cells. The inactivation of B. henselae by UV or heat treatment abolished its stimulatory activity, suggesting that live bacteria is necessary for the growth stimulation effect. To investigate the role of direct contact, live B. henselae were separated from HUVECs by a filter membrane (Millicell-CM insert). Even under this condition, an enhanced proliferation of HUVECs was observed. However, no morphological changes in the HUVECs were apparent compared to the B. henselae -infected cells. Furthermore, we isolated a nonpiliated strain of B. henselae that is unable to attach to and enter into endothelial cells. The nonpiliated strain possessed the ability to stimulate the proliferation of cocultivated HUVECs the same as the piliated strain. Moreover, the culture supernatants of B. henselae were also able to induce HUVEC proliferation. Our results indicate that the stimulation of HUVEC proliferation by B. henselae is mediated by soluble factor(s) secreted from the bacteria.

B cell epitope mapping of the bacterial superantigen staphylococcal enterotoxin B: the dominant epitope region recognized by intravenous IgG.

We showed that i.v. IgG contains Abs against a major group of bacterial superantigens, and that they can inhibit superantigen-elicited T cell activation. The B cell epitope region of the superantigen and the inhibitory mechanism have remained unknown. To analyze the dominant B cell epitopes on the bacterial superantigen SEB (staphylococcal enterotoxin B), we constructed fusion proteins of SEB deletion mutants, and the reactivities of these recombinant proteins to i.v. IgG and healthy human sera were evaluated by means of immunoblotting. Intravenous IgG and healthy human sera mostly recognized the C-terminal fragment (amino acid (aa) 133-239). The C-terminally truncated protein (aa 1-228) and the truncated mutant delta 225-234 lost reactivity, while the truncated protein (aa 1-234) did not, suggesting that the region (aa 225-234) is the dominant B cell epitope. The mutant, in which residues 226-229 of SEB were exchanged for residues 209-212 of streptococcal pyrogenic exotoxin A, reduced the reactivity with the C-terminal region-specific IgG purified by affinity chromatography. The C-terminal region-specific IgG inhibited SEB-elicited T cell activation, suggesting that this Ab that recognizes the epitope functions as the humoral defensive factor against SEB in humans. Furthermore, the assumed epitope region was homology to the residues (aa 32-41) of human thymopoietin, containing the biologic active site.

Mitral regurgitation may be related with previous streptococcal infection.

UNLABELLED: We measured anti M protein antibody (AMPA) titres in children with idiopathic mitral regurgitation (MR), streptococcal infection, rheumatic fever (RF), post-streptococcal acute glomerulonephritis (AGN) and normal healthy children. We investigated the association of MR with streptococcal infection and whether high AMPA titres can be used as persisting evidence of previous streptococcal infection. AMPA titres were measured with an enzyme-linked immunosorbent assay. We found significantly higher antibody titres in patients with MR and in streptococcal infection, RF, and AGN than in healthy controls. In the MR group (n = 15), 54% patients had AMPA titres above the 90th percentile value that was found in normal controls. An elevated AMPA titre persisted for a long period even when the anti-streptolysin O titres had declined to normal in RF patients. Our data suggest that the high AMPA titres in MR should be further investigated to clarify the probable association with previous streptococcal infection. CONCLUSION: High AMPA titre is a risk factor for developing complications after streptococcal infection. Our serological evidence suggests that in some patients, MR may be related to previous streptococcal infection.

Antigenic specificity of lymphocytes isolated from valvular specimens of rheumatic fever patients.

T cell lines were established from both valvular specimens and peripheral blood lymphocytes from seven patients with well documented rheumatic heart disease. These cell lines were stimulated with either PHA or streptococcal antigens. Proliferation assays revealed that both valvular and peripheral blood T cell lines reacted to cell wall (CW) and cell membrane (CM) antigens obtained from rheumatic fever associated group A streptococci and not to nephritogenic strains. None of the cell lines reacted to M protein, myosin or other mammalian cytoskeletal proteins. The unique reactivity of rheumatic fever T cell lines only to cellular structures obtained from rheumatogenic strains suggests that these lines react to epitopes specific for antigens obtained from these strains.