Modulation of complement fixation and the phlogistic capacity of group A, B, and D streptococci by human lysozyme acting on their cell walls

Enterococcus faecium and Pediococcus acidilactici deteriorate Enterobacteriaceae-induced depression and colitis in mice

Gut dysbiosis is closely associated with the outbreak of inflammatory bowel disease (IBD) and psychiatric disorder. The Enterobacteriaceae population was higher in the feces of patients with inflammatory bowel disease (IBD-F) than in those of healthy control volunteers (HC-F). The Enterococcaceae and Lactobacillaceae populations were higher in the feces of IBD patients with depression (IBD/D+-F) vs. the feces of IBD patients without depression (IBD/D--F). Therefore, we examined the effects of Klebsiella oxytoca, Escherichia coli, Cronobacter sakazakii, Enterococcus faecium, and Pediococcus acidolactici overpopulated in IBD/D+-F and their byproducts LPS and exopolysaccharide (EPS) on the occurrence of depression and colitis in mice. Oral gavages of Klebsiella oxytoca, Escherichia coli, and Cronobacter sakazakii belonging to Enterobacteriaceae, singly or together, caused dose-dependently colitis and depression-like behaviors in germ-free and specific-pathogen-free mice. Although Enterococcus faecium and Pediococcus acidolactici did not significantly cause colitis and depression-like behaviors, they significantly deteriorated Klebsiella oxytoca- or Escherichia coli-induced colitis, neuroinflammation, and anxiety/depression-like behaviors and increased blood LPS, corticosterone, and IL-6 levels. The EPSs from Enterococcus faecium and Pediococcus acidolactici also worsened Klebsiella oxytoca LPS-induced colitis, neuroinflammation, and depression-like behaviors in mice and increased the translocation of fluorescein isothiocyanate-conjugated LPS into the hippocampus. However, Bifidobacterium longum, which was lower in IBD/D+-F vs. IBD/D--F, or its EPS suppressed them. In conclusion, Enterococcus faecium and Pediococcus acidolactici, known as a probiotic strain, and their EPSs may be a risk factor for the outbreak of depression and IBD.

Curvature of synthetic and natural surfaces is an important target feature in classical pathway complement activation

The binding of Abs to microbial surfaces followed by complement activation constitutes an important line of defense against infections. In this study, we have investigated the relationship between complement activation and the binding of human IgM Abs to surfaces with different curvatures. IgM Abs to dextran were shown to activate complement potently on dextran-coated particles having a diameter around 250 nm, whereas larger (600 nm) particles were less potent activators. This selectivity regarding particle dimension was also found for complement activation by colloidal substances of microbial origin. Peptidoglycan (PGN) is the major chemical component in the cell wall of Gram-positive bacteria. Fragments of purified PGN with sizes of approximately 100 nm promoted complement activation effectively through the classical pathway. By contrast, larger or smaller fragments of PGN did not activate complement strongly. A careful analysis of PGN fragments released during planctonic growth of Staphylococcus aureus showed that these include curvatures that would permit strong IgM-mediated complement activation, whereas the curvature of intact cells would be less effective for such activation. Consistently, we found that the suspended PGN fragments were strong activators of complement through the classical pathway. We suggest that these fragments act as decoy targets for complement activation, providing protection for S. aureus against the host immune response to infection.

Phlogistic properties of peptidoglycan-polysaccharide polymers from cell walls of pathogenic and normal-flora bacteria which colonize humans

PG-PS polymers which can induce experimental chronic inflammation in joints and other tissues can be isolated from the cell walls of human pathogens, such as group A streptococci, as well as from certain indigenous bacterial species which colonize the human intestinal tract. The structural and biological properties that are required for cell wall fragments to express this remarkable activity are still not well defined, but polymer size, resistance to tissue enzymes, and capacity to sustain activation of complement, macrophages, neutrophils, and T cells are properties associated with the most active preparations. There is increasing evidence that PG-PS structures with arthropathogenic activity occur in the human intestinal lumen and that these polymers can be translocated systemically. These observations support the concept that PG-PS, derived from a variety of bacterial species, can be part of the etiology of rheumatoid arthritis and other chronic inflammatory diseases. Since the PG component provides a common element to which all individuals are exposed, it follows that susceptibility is related to efficiency of disposal of bacterial cell wall debris, as well as to cytokine networks and immune cell function (51).

A major surface protein on group A streptococci is a glyceraldehyde-3-phosphate-dehydrogenase with multiple binding activity

The surface of streptococci presents an array of different proteins, each designed to perform a specific function. In an attempt to understand the early events in group A streptococci infection, we have identified and purified a major surface protein from group A type 6 streptococci that has both an enzymatic activity and a binding capacity for a variety of proteins. Mass spectrometric analysis of the purified molecule revealed a monomer of 35.8 kD. Molecular sieve chromatography and sodium dodecyl sulfate (SDS)-gel electrophoresis suggest that the native conformation of the protein is likely to be a tetramer of 156 kD. NH2-terminal amino acid sequence analysis revealed 83% homology in the first 18 residues and about 56% in the first 39 residues with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of eukaryotic or bacterial origin. This streptococcal surface GAPDH (SDH) exhibits a dose-dependent dehydrogenase activity on glyceraldehyde-3-phosphate in the presence of beta-nicotinamide adenine dinucleotide both in its pure form and on the streptococcal surface. Its sensitivity to trypsin on whole organism and its inability to be removed with 2 M NaCl or 2% SDS support its surface location and tight attachment to the streptococcal cell. Affinity-purified antibodies to SDH detected the presence of this protein on the surface of all M serotypes of group A streptococcal tested. Purified SDH was found to bind to fibronectin, lysozyme, as well as the cytoskeletal proteins myosin and actin. The binding activity to myosin was found to be localized to the globular heavy meromyosin domain. SDH did not bind to streptococcal M protein, tropomyosin, or the coiled-coil domain of myosin. The multiple binding capacity of the SDH in conjunction with its GAPDH activity may play a role in the colonization, internalization, and the subsequent proliferation of group A streptococci.

Stimulation of complement component C3 synthesis in macrophagelike cell lines by group B streptococci

Complement levels and complement activation are key determinants in streptococcus-induced inflammatory responses. Activation of macrophage functions, such as complement synthesis, by group B streptococci (GBS) was examined as a possible component of GBS-induced chronic inflammation. Using an enzyme-linked immunosorbent assay, secreted C3 from mouse macrophagelike cell lines (PU5-1.8 and J774A.1) was monitored after cultivation with GBS. Whole, heat-killed GBS (1 to 10 CFU per macrophage) of both type Ia and III strains induced 25 to 300% increases in secreted C3 in both cell lines after a 24-h cultivation. GBS-treated cell lines exhibited increases in secreted lysozyme (10%) and in cellular protein (25 to 50%). Inhibition of macrophage phagocytosis by cytochalasin B inhibited GBS stimulation of C3. Purified cell walls of GBS type III strain 603-79 (1 to 10 micrograms/ml) also enhanced C3 synthesis. Local enhancement of macrophage C3 production by ingested streptococci or by persistent cell wall antigens may serve to promote chronic inflammatory responses.

Effect of acetylation on arthropathic activity of group A streptococcal peptidoglycan-polysaccharide fragments

Purified group A streptococcal peptidoglycan-polysaccharide (PG-PS) fragments were either de-O-acylated, or acetylated and then de-O-acylated to yield N-acetylated PG-PS. Native PG-PS was poorly degraded, N-acetylated PG-PS was extensively degraded, and de-O-acylated PG-PS was only slightly degraded by hen egg white lysozyme. N-acetylated PG-PS was also extensively degraded by human lysozyme and partially degraded by rat serum or rat liver extract. After a single intraperitoneal injection of rats with a sterile, aqueous suspension, all PG-PS preparations induced acute arthritis. The acute arthritis induced by N-acetylated PG-PS was significantly more severe than that induced by native PG-PS; that induced by de-O-acylated PG-PS was of intermediate severity. After the acute reaction, rats injected with native PG-PS developed chronic relapsing erosive synovitis which remained severe for the duration of the experiment (83 days). In contrast, joint inflammation induced by N-acetylated PG-PS resolved within 6 weeks with little evidence of recurrent disease. Chronic arthritis induced by de-O-acylated PG-PS was of intermediate severity. In another assay of arthropathic activity, the arthritis in all rat ankle joints, which had been injected directly with native PG-PS, could be reactivated 3 weeks later by the intravenous injection of a small dose of PG. In contrast, only 50% of the joints initially injected with de-O-acylated PG-PS and none of the joints injected with N-acetylated PG-PS could be reactivated. These studies support the concepts that the resistance of PG-PS to muralytic digestion is crucial for chronic arthropathic activity and that the nature and degree of PG acetylation are important molecular determinants of the phlogistic activities of PG-PS polymers.