Role of antibodies in the opsonization of Yersinia spp

Passive immunization with monoclonal antibodies specific for lipopolysaccharide (LPS) O-side chain protects mice against intravenous Yersinia enterocolitica serotype O:3 infection

Passive immunization with monoclonal antibodies specific for the lipopolysaccharide (LPS) O-side chain protected mice against intravenously given lethal doses of Yersinia enterocolitica O:3 bacteria. On the other hand, passive immunization with monoclonal antibody specific for the LPS core oligosaccharide did not protect mice. Neither antibody was able to protect mice against orally given lethal doses of bacteria. These results indicate that the O-side chain functions as an important antigenic structure during infection, and that immunity to it probably offer protection also in the in vivo situation.

Role of Yops in inhibition of phagocytosis and killing of opsonized Yersinia enterocolitica by human granulocytes

The virulence plasmid of Yersinia enterocolitica codes for the production of the outer membrane protein YadA and the secretion of several proteins, called Yops, which may play a role in the interaction between granulocytes and this bacterium. We investigated whether the expression of YadA or the secretion of Yops affected the phagocytosis and killing of opsonized Y. enterocolitica by human granulocytes. The rates of phagocytosis and killing of Y. enterocolitica by granulocytes in suspension in the presence of rabbit Yersinia antibodies and complement were determined by microbiological assays. In addition, noningested cell-adherent bacteria were differentiated from ingested yersiniae by immunofluorescence microscopy. Plasmid-bearing opsonized Y. enterocolitica was able to inhibit phagocytosis and killing by human granulocytes. The inhibition of phagocytosis was specific for the plasmid-bearing strain of Y. enterocolitica, since granulocytes were still able to phagocytose and kill Staphylococcus aureus in the presence of Y. enterocolitica. Plasmid-cured Y. enterocolitica was readily phagocytosed and killed by these cells. To investigate the role of YadA or Yops in the inhibition of phagocytosis by granulocytes, the phagocytosis of mutant strains unable to express YadA or to secrete Yops was studied. A Y. enterocolitica mutant unable to secrete Yops lost its ability to inhibit phagocytosis; a mutant expressing only YadA was readily ingested by granulocytes. These results indicate that after attachment of opsonized Y. enterocolitica to granulocytes, Yops play an important role in inhibiting the ingestion of Y. enterocolitica by human granulocytes.

Adhesion protein YadA of Yersinia species mediates binding of bacteria to fibronectin

The interaction between fibronectin and Yersinia strains was studied. Wild-type Y. enterocolitica strains expressing the virulence-plasmid-encoded adhesion protein YadA adhered strongly to fibronectin-coated coverslips, while their plasmid-cured variants expressed weaker binding. The cloned yadA gene of Y. enterocolitica or Y. pseudotuberculosis conferred fibronectin-binding ability both to Escherichia coli and to Y. psuedotuberculosis strains lacking the YadA protein. The YadA protein did not mediate binding to isolated fragments of fibronectin or to soluble fibronectin.

Clinical manifestations of Yersinia pseudotuberculosis infection in children

The clinical manifestations of infection were analysed during an outbreak of 34 cases of Yersinia pseudotuberculosis serotype Ia infection. The diagnosis was based on the results of enzyme immunoassay and verified by stool culture in five cases. The first four patients were pupils from the same school, and information on any signs and symptoms of infection was obtained by questionnaire from pupils of the school. A blood sample was obtained from 101 children. Strong IgM and IgG antibody responses to Yersinia pseudotuberculosis Ia were found in 13 (25%) of the 52 pupils who reported signs and symptoms of infection and in 9 (18%) of the 49 with no manifestations of infection. The vigorous immune response also resulted in effective opsonization of the causative microorganism. The most common symptoms were fever and abdominal pain. Three children operated on because of suspected appendicitis were found to have mesenteric lymphadenitis. Only one patient developed reactive arthritis. Analysis showed that a remarkable proportion of Yersinia pseudotuberculosis infections may be subclinical, and that individual Yersinia pseudotuberculosis strains may have different capacities to cause postinfection complications.

Serum opsonic capacity against Yersinia enterocolitica O:3 in yersiniosis patients with or without reactive arthritis

The opsonic capacity of 45 sera from patients with reactive arthritis after Yersinia enterocolitica O:3 infection and of 45 matched sera from yersiniosis patients without post-infection complications was studied at 1-3 months, 5-8 months and 12-20 months after the onset of the infection. Antibody-mediated opsonization of virulence-plasmid-containing Y. enterocolitica O:3 was studied by measuring complement-fixation on opsonized bacteria and opsonophagocytic function of the polymorphonuclear leucocytes (PMN). The PMN response against bacteria pre-opsonized by heat-inactivated sera was measured by using a chemiluminescence (CL) assay. The fixation of complement Clq and C3 on bacteria was determined by flow cytometry using fluorescein-conjugated Clq- and C3c-antisera. All the sera were strongly opsonic at the onset of the infection, and this capacity persisted in most of the patients still at the end of the follow-up. No difference was observed in complement-fixing capacity between the sera of the two groups, but the sera from arthritic patients showed stronger augmentation of PMN CL response at the early phase of the infection (P = 0.005 in the presence of complement, P = 0.04 in the absence of complement). These results suggest that enhanced opsonic capacity may play a role in the development of Yersinia-triggered reactive arthritis by leading to strong activation of the PMN and, consequently, to release of inflammatory mediators.

The role of infectious agents in the spondylarthropathies

The clinical similarities of the spondylarthropathies and their frequent association with both HLA B27 and microbial infections suggest common pathogenetic mechanisms. The latter may include deposition of immune complexes containing bacterial antigens. or cross-reactivity of such antigens with host target tissue or responding cell antigens. Enteric bacteria, chlamydia and mycoplasma are all candidate etiologic agents, but proof is difficult because they are often found as normal flora, although only genetically susceptible individuals may acquire disease, and many patients have been treated with antibiotics before they can be studied. Nonetheless, a role for endogenous bacteria in reactive arthritis at least seems certain, and should stimulate further investigation into similar pathogenetic mechanisms in other chronic arthritides.