Yersinia Outer Membrane Proteins Research Articles

Seroepidemiological survey of pathogenic Yersinia in domestic pigs in Chiba Prefecture, Japan.

This study aimed to investigate the prevalence of antibodies against pathogenic Yersinia such as Y. enterocolitica and Y. pseudotuberculosis in domestic pigs. A total of 650 serum samples from pigs in nine regions of the Chiba Prefecture in Japan, were tested using plasmid-encoded Yersinia outer membrane protein (Yops) antigen ELISA. The cutoff value was calculated using 20 pathogenic Yersinia-free pig serum samples. According to the cutoff value, 246 (37.8%) pigs from seven regions were considered seropositive for pathogenic Yersinia during the study period. These results indicate that pathogenic Yersinia is widespread in pigs in Chiba, which may become the source of human yersiniosis in this region.

TAK1 inhibition elicits mitochondrial ROS to block intracellular bacterial colonization

Mitogen-activated protein kinase kinase kinase 7 (MAP3K7), known as TAK1, is an intracellular signaling intermediate of inflammatory responses. However, a series of mouse Tak1 gene deletion analyses have revealed that ablation of TAK1 does not prevent but rather elicits inflammation, which is accompanied by elevation of reactive oxygen species (ROS). This has been considered a consequence of impaired TAK1-dependent maintenance of tissue integrity. Contrary to this view, here we propose that TAK1 inhibition-induced ROS are an active cellular process that targets intracellular bacteria. Intracellular bacterial effector proteins such as Yersinia's outer membrane protein YopJ are known to inhibit TAK1 to circumvent the inflammatory host responses. We found that such TAK1 inhibition induces mitochondrial-derived ROS, which effectively destroys intracellular bacteria. Two cell death-signaling molecules, caspase 8 and RIPK3, cooperatively participate in TAK1 inhibition-induced ROS and blockade of intracellular bacterial growth. Our results reveal a previously unrecognized host defense mechanism, which is initiated by host recognition of pathogen-induced impairment in a host protein, TAK1, but not directly of pathogens.

TAK1 Inhibition Elicits Mitochondrial ROS to Block Intracellular Bacterial Colonization

Mitogen activated protein kinase kinase kinase 7 (MAP3K7), known as TAK1, is an intracellular signaling intermediate of inflammatory responses. However, a series of mouse Tak1 gene deletion analysis has revealed that ablation of TAK1 does not prevent but rather elicits inflammation, which is accompanied by elevation of reactive oxygen species (ROS). These have been considered as consequences of non-physiological loss of TAK1. Contrary to this view, here we propose that TAK1 inhibition-induced ROS are an active cellular process that targets intracellular bacteria. Intracellular bacterial effector proteins such as Yersinia's outer membrane protein YopJ are known to inhibit TAK1 to circumvent the inflammatory host responses. We found that such TAK1 inhibition particularly induces mitochondrial-derived ROS, which effectively destroys intracellular bacteria. Our results reveal a previously unrecognized host defense mechanism linking inhibition of inflammatory signaling with mitochondrial ROS.

Yersinia pestis and plague: an updated view on evolution, virulence determinants, immune subversion, vaccination and diagnostics

Plague is a vector-borne disease caused by Yersinia pestis. Transmitted by fleas from rodent reservoirs, Y. pestis emerged less than 6000 years ago from an enteric bacterial ancestor through events of gene gain and genome reduction. It is a highly remarkable model for the understanding of pathogenic bacteria evolution, and a major concern for public health as highlighted by recent human outbreaks. A complex set of virulence determinants, including the Yersinia outer membrane proteins (Yops), the broad range protease Pla, pathogen-associated molecular patterns (PAMPs) and iron capture systems play critical roles in the molecular strategies that Y. pestis employs to subvert the human immune system, allowing unrestricted bacterial replication in lymph nodes (bubonic plague) and in lungs (pneumonic plague). Some of these immunogenic proteins as well as the capsular antigen F1 are exploited for diagnostic purposes, which are critical in the context of the rapid onset of death in the absence of antibiotic treatment (less than a week for bubonic plague and less than 48 h for pneumonic plague). In here, we review recent research advances on Y. pestis evolution, virulence factors function, bacterial strategies to subvert mammalian innate immune responses, vaccination and problems associated to pneumonic plague diagnosis.

Assessment of the efficacy of an autogenous vaccine against Yersinia pseudotuberculosis in young Merino sheep

AIMSTo assess the efficacy of an autogenous vaccine against Yersinia pseudotuberculosis III in preventing clinical disease and deaths due to yersiniosis in young Merino sheep, and to determine the effect of vaccination on the prevalence of faecal shedding of pathogenic Yersinia spp., daily liveweight gain, and development of antibodies to Yersinia spp. following vaccination and natural exposure.METHODSIn six groups (three groups each from two farms) of young Merino sheep, 148–150 animals were systematically allocated to be vaccinated twice with an autogenous, formalin- killed bacterin vaccine containing Y. pseudotuberculosis serotype III or to remain non-vaccinated. All vaccinated and non-vaccinated sheep were run together in their original groups throughout the trial. Faecal and blood samples were collected, and liveweight measured, at the time of vaccination and subsequently over a 6-month period to determine faecal shedding of Y. enterocolitica and Y. pseudotuberculosis, seroprevalence of antibodies to Yersinia outer membrane proteins (YOP) and changes in liveweight.RESULTSNone of the six trial groups experienced an outbreak of clinical yersiniosis during the study period. On Farm A, the prevalence of shedding of either or both Yersinia spp. was <40% on all but one sampling occasions. On Farm B the prevalence of shedding of both Yersinia spp. peaked at 98%, 96 days after vaccination. Mean liveweight and daily liveweight gain at the end of the study were similar in vaccinated and non-vaccinated groups on both farms (p>0.1), as was the prevalence of faecal shedding of Yersinia spp. (p>0.2), and the proportion of animals that became seropositive for antibodies to YOP following vaccination (p>0.1).CONCLUSIONS AND CLINICAL RELEVANCEThis vaccine had, at most, limited effects on seroconversion and, under the conditions of this study, had no demonstrable impact on liveweight, mean daily liveweight gain or faecal shedding of Yersinia spp. Further studies are needed to determine the efficacy of this vaccine during outbreaks of yersiniosis or following experimental challenge with pathogenic Yersinia spp..

Comparison of Lipopolysaccharide and Protein Immunogens from Pathogenic Yersinia enterocolitica Bio-serotype 1B/O:8 and 2/O:9 using SDS-PAGE

ObjectiveYersinia enterocolitica is an extracellular pathogen and its related antigens interact with the host immune system. We investigated the difference in immunological characteristics between a highly pathogenic and poorly pathogenic strain of Y. enterocolitica. MethodsWe used SDS-PAGE and western blotting to characterize lipopolysaccharide (LPS), Yersinia outer membrane proteins (Yops), membrane proteins, and whole-cell proteins from poorly pathogenic Y. enterocolitica bio-serotype 2/O:9, isolated from China, and highly pathogenic bio-serotype 1B/O:8, isolated from Japan. ResultsThese two strains of Y. enterocolitica had different LPS immune response patterns. Comparison of their Yops also showed differences that could have accounted for their differences in pathogenicity. The membrane and whole-cell proteins of both strains were similar; immunoblottting showed that the 35 kD and perhaps the 10 kD proteins were immunogens in both strains. ConclusionThe major antigens of the two strains eliciting the host immune response were the LPS and membrane proteins, as shown by comparing protein samples with reference and purified preparations.

Development of a test system for the serodiagnosis of yersiniases by an immunoblot test

The pseudotuberculosis pathogen Y. pseudotuberculosis and the enteric yersiniasis pathogen Y. enterocolitica may cause both acute and chronic diseases. Widely practically used diagnostic methods are effective in the acute period of the diseases whereas diagnosis verification in the protracted and chronic course of yersiniases remains an urgent problem. For solution of this problem, the authors have developed a cost-effective test system for the serodiagnosis of yersiniases by an immunoblot test, by applying the recombinant proteins of recombinant Yersinia outer membrane proteins, such as YopH (51 kD), YopM (44 kD), YopD (35 kD), and YopE (23 kD). As compared to indirect hemagglutination test, agglutination test, and enzyme immunoassay, the immunoblot test has a high sensitivity and a high specificity and may be promising mainly in diagnosing the chronic forms of Yersinia infection.

Relevance of Yersinia Outer Membrane Proteins in Collagenous and Lymphocytic Colitis

Relevance of Yersinia Outer Membrane Proteins in Collagenous and Lymphocytic Colitis

The Effects of Low-Shear Mechanical Stress on Yersinia pestis Virulence

Manned space exploration has created a need to evaluate the effects of spacelike stress on pathogenic and opportunistic microbes astronauts could carry with them to the International Space Station and beyond. Yersinia pestis (YP) causes bubonic, septicemic, and pneumonic plague and is capable of killing infected patients within 3-7 days. In this study, low-shear modeled microgravity (LSMMG), a spacelike stress, was used to physically stress YP; and its effects on proliferation, cold growth, and type III secretion system (T3SS) function were evaluated. YP was grown to saturation in either LSMMG or normal gravity (NG) conditions prior to being used for RAW 246.7 cell infections, HeLa cell infections, and Yop secretion assays. A mutant strain of YP (ΔyopB) that lacks the ability to inject Yersinia outer membrane proteins (Yops) into the host cell was used as a negative control in cell infection experiments. Our experimental results indicate that YP cultivated under LSMMG resulted in reduced YopM production and secretion compared to its NG-grown counterpart. Similarly, NG-grown YP induced more cell rounding in HeLa cells than did the LSMMG-grown YP, which suggests that LSMMG somehow impairs T3SS optimum function. Also, LSMMG-grown YP used to infect cultured RAW 246.7 cells showed a similar pattern of dysfunction in that it proliferated less than did its NG-grown counterpart during an 8-hour infection period. This study suggests that LSMMG can attenuate bacterial virulence contrary to previously published data that have demonstrated LSMMG-induced hypervirulence of other Gram-negative enterics.

Seroepidemiological Survey of Pathogenic Yersinia in Breeding Squirrel Monkeys in Japan

To investigate the prevalence of antibodies to pathogenic Yersinia in breeding squirrel monkeys, the serum samples of 252 squirrel monkeys from 9 zoological gardens in Japan were tested by ELISA using plasmid-encoded Yersinia outer membrane protein (Yops) as the antigen. The cutoff value was calculated by using the serum samples of the squirrel monkeys from Suriname, where no prevalence of pathogenic Yersinia have been reported. According to the cutoff value, 164 of 252 (65.1%) squirrel monkeys were considered positive against pathogenic Yersinia. These positive monkeys belonged to 8 of the 9 zoological gardens, and the percentage of the seropositive monkeys ranged from 22.2 to 89.4%. Furthermore, in one zoological garden, the positive rate of the squirrel monkeys which were over 1 year old (95.7%) was significantly higher than those which were under 1 year old (23.3%). These results suggested that pathogenic Yersinia is highly prevalent among breeding monkeys in Japan.

Characterization of immune responses to Yersinia pestis infection: resistant versus susceptible mice(129.29)

Abstract We have previously reported that inbred B10.T(6R) mice are resistant to Yersinia pestis infection, compared to susceptible strains, e.g. Swiss Webster mice; the mean LD50's for B10.T(6R) females is 14000 CFU's, compared to Swiss Webster females, at 22 CFU's. Interestingly, B10.T(6R) mice demonstrated a more robust pro-inflammatory response early in infection, and a lesser anti-inflammatory response later on, when compared to susceptible Swiss Webster mice. Significantly higher levels of TNF-alpha were detected in B10.T(6R) on day 1 while TNF-alpha responses were delayed in Swiss Webster mice. Conversely, IL-10 levels were not changed in B10.T(6R) mice while IL-10 levels increased significantly in Swiss Webster mice. Yersinia outer membrane proteins (YOP) are translocated into the host cell's cytoplasm via a type three secretion system. After contact with a eukaryotic cell, YOPs then interact with cellular components to disrupt the host's immune response and induce the production of suppressive cytokines, e.g. IL-10. We postulate that the resistant B10.T(6R) strain of mice are able to overcome initial infection with Y. pestis through higher levels of pro-inflammatory cytokines and decreased levels of immune suppressive cytokines later in infection.

Cross-reaction between Yersinia outer membrane proteins and anti-Borreli antibodies in sera of patients with Lyme disease

Diagnosis of Yersinia infections accompanied by reactive arthritis could be complicated by cross-reaction with other arthritogenic bacteria. The possible cross-reaction between Yersinia antigens and anti-Borrelia antibodies in blood sera of patients with Lyme disease was studied. The occurrence of specific IgA, IgG and IgM antibodies was analyzed in serum samples from 30 patients with Yersinia-triggered reactive arthritis, 30 patients with Lyme disease and five samples from healthy blood donors. For anti-Borrelia IgG antibodies, cross-reaction was detected with YopH, YopB, V-ag, YopD, YopN, YopP and YopE, and for IgA with YopD. For IgM, no cross-reaction was detected. Owing to cross-reactivity with Borrelia, the diagnosis of Yersinia-triggered reactive arthritis should be based on a combination of serological and clinical findings.

Too early to dismiss Yersinia enterocolitica infection in the aetiology of Graves’ disease: evidence from a twin case–control study

Yersinia enterocolitica (YE) infection has long been implicated in the pathogenesis of Graves' disease (GD). The association between YE and GD could, however, also be due to common genetic or environmental factors affecting the development of both YE infection and GD. This potential confounding can be minimized by investigation of twin pairs discordant for GD. To examine whether YE infection is associated with GD. We first conducted a classical case-control study of individuals with (61) and without (122) GD, and then a case-control study of twin pairs (36) discordant for GD. Immunoglobulin (Ig)A and IgG antibodies to virulence-associated Yersinia outer membrane proteins (YOPs) were measured. The prevalence of YOP IgA and IgG antibodies. Subjects with GD had a higher prevalence of YOP IgA (49%vs. 34%, P = 0.054) and YPO IgG (51%vs. 35%, P = 0.043) than the external controls. The frequency of chronic YE infection, reflected by the presence of both IgA and IgG YOP antibodies, was also higher among cases than controls (49%vs. 33%, P = 0.042). Similar results were found in twin pairs discordant for GD. In the case-control analysis, individuals with GD had an increased odds ratio (OR) of YE infection: IgA 1.84 (95% CI 0.99-3.45) and IgG 1.90 (95% CI 1.02-3.55). In the co-twin analysis, the twin with GD also had an increased OR of YE infection: IgA 5.5 (95% CI 1.21-24.81) and IgG 5.0 (95% CI 1.10-22.81). The finding of an association between GD and YE in the case-control study and within twin pairs discordant for GD supports the notion that YE infection plays an aetiological role in the occurrence of GD, or vice versa. Future studies should examine the temporal relationship of this association in more depth.

Role of TNFRp55 in Yersinia enterocolitica O:3-induced arthritis: triggering bacterial antigens and articular immune response

The pathogenesis of reactive arthritis (ReA), an aseptic synovitis that follows an extra-articular infection, is incompletely known. We studied the impact of tumour necrosis factor receptor (TNFR) p55 deficiency on the progression to ReA after oral Yersinia enterocolitica O:3 infection, the Yersinia antigens triggering articular inflammation and a possible articular TNFRp55-mediated mechanism that protects against ReA. Wild-type C57BL/6 and TNFRp55-/- mice were orogastrically infected with Y. enterocolitica O:3 and monitored for survival and arthritis development. The bacterial load was determined in mesenteric lymph nodes (MLNs), the spleen and joints. Interferon (IFN)-gamma, TNF-alpha and IL-10 mRNA expression in MLN and joints were analysed by reverse transcription-polymerase chain reaction (RT-PCR). Articular antibodies to Yersinia antigens, TNF-alpha protein and nitric oxide (NO) levels were assessed. Acute arthritis was evaluated after joint injection of Yersinia antigens. The survival rate was 60% in TNFRp55-/- mice. They showed impaired bacterial clearance in MLN, the spleen and joints, and excessive mRNA expression of pro-inflammatory cytokines in MLN. Clinical and histological examinations revealed that TNFRp55-/- mice developed severe arthritis. Moreover, augmented articular outer membrane protein (OMP)-specific antibodies and TNF-alpha but impaired NO levels were detected in TNFRp55-/- mice. Synovial inflammatory response was detected by joint OMP injection. TNFRp55-mediated immune mechanisms prevent ReA development after oral infection with Y. enterocolitica O:3. Yersinia OMPs are the relevant antigens triggering ReA. NO induction through TNFRp55 signalling could have a local antibacterial function to prevent ReA. This study could contribute to ReA-specific therapeutic studies.

605. Long-Term Protection Afforded by a Single Administration of an Ad-Based Anti-Y. pestis Vaccine Against a Lethal Respiratory Challenge with Y. pestis

The aerosol form of the bacterium Yersinia pestis causes the pneumonic plague, a virulent and rapidly fatal disease that develops within days post-infection. In the context of a bioterror threat, an ideal anti-plague vaccine should elicit rapid, robust and long-acting protective immunity after a single dose. At present, no plague vaccines are available for use in the USA. One candidate for developing a subunit vaccine is the Yersinia pestis V antigen, a protein that influences the function of the Yersinia outer membrane proteins (Yops) virulence factors and has local anti-inflammatory effects in the host.

67. Protective Immunity Against Yersinia pestis in Mice Immunized with an Ad-Based Vaccine Vector Expressing the Y. pestis F1 and V Antigens

The aerosol form of the bacterium Yersinia pestis causes the pneumonic plague, an extremely virulent and rapidly fatal disease that develops within days post-infection. In the context of a bioterror threat, an effective anti-plague vaccine must elicit rapid, robust and long acting protective immunity after a single dose. At present, no plague vaccines are available for use in the USA. Two subunits of Y. pestis, fraction 1 (F1) and V antigen have been identified as vaccine candidates based on: (1) F1 antigen is a temperature-regulated capsular protein of Y. pestis with anti-phagocytic activity in the host; (2) V antigen has local anti-inflammatory effects and influences the function of important virulence factors such as the Yersinia outer membrane proteins (Yops). It is known that protective immunity against Y. pestis challenge can be induced by multiple immunizations with recombinant F1 and V proteins and immediate protection can be achieved by passive transfer of immune sera against these antigens. Based on the knowledge that adenovirus (Ad) gene transfer vectors act as adjuvants in eliciting host immunity against the transgene they carry, replication-defective Ad gene transfer vectors encoding either the Y. pestis V antigen or the F1 protein (AdsecV and AdsecF1, respectively) were constructed. The F1 and V antigen genes were synthesized by an overlap PCR strategy using mammalian preferred codons, and fused to the human Ig signal sequence for extracellular secretion. We tested the hypothesis that AdsecV and AdsecF1 can stimulate strong protective immune responses without a requirement for repeat administration. To test the efficacy of the vaccines, BALB/c mice were immunized with a single intramuscular administration of either vector at a dose of 108 to 1011 particles units (pu). Four wk after immunization, mice were challenged in a BSL3 experimental animal facility (n=10/group) by the intranasal route with 3103 cfu of the fully virulent Yersinia pestis strain, CO92. At challenge time, anti-V antigen IgG reciprocal titers from AdsecV–immunized mice (n=10/group) were 666137 (108 pu), 3045735 (109 pu), 97032193 (1010 pu), and 7611215914 (1011 pu). In contrast, anti-F1 antigen IgG reciprocal titers from AdsecF1-immunized mice (n=10/group) were much lower with 122 (108 pu), 9135 (109 pu), 1154138 (1010 pu), and 939157 (1011 pu). All (10/10) of the animals survived the Y. pestis challenge in the group vaccinated with 1011 pu AdsecV, and 40% (4/10) survived in the 1010 pu AdsecV dose, while in all the other experimental groups immunized with AdsecV and in the control groups the mice died within 2 to 5 days after challenge. No mice vaccinated with AdsecF1 survived the Y. pestis challenge. These observations suggest that an Ad-based vaccine encoding for the V antigen of Y. pestis (AdsecV) is an excellent candidate as a effective single dose vaccine against the plague.

Differences in Heat Resistance among Pathogenic Yersinia enterocolitica Depended on Growth Temperature and Serotype

To gain a better understanding about the effect of growth temperature on heat resistance of Yersinia enterocolitica, we determined decimal reduction times at 60°C (D60-values) for O:3; O:5,27; O:8; and O:9 strains harboring virulence plasmid coding for Yersinia outer membrane protein and experimentally virulence plasmid–deleted strains after they were grown to stationary phase at 7, 25, or 37°C. Bacteria were inoculated into Trypticase soy broth and were incubated at several temperatures. D60-values of O:3; O:5,27; and O:8 strains were larger when they were grown at 37°C than at 7 or 25°C, despite the presence or absence of virulence plasmids. However, similar D60-values were observed in O:9 strains, despite growth at 7, 25, or 37°C. The results indicate two types of Y. enterocolitica strains, growth temperature–dependent and –independent, and a Yersinia outer membrane protein that is not directly involved in growth temperature–dependent heat resistance.

Yersinia Yop-Specific IgA antibodies in Hungarian blood donors

Sera of 112 healthy Hungarian blood donors were tested for the presence of Yersinia enterocolitica and Y. pseudotuberculosis-specific agglutinins by tube agglutination, and for that of yersinia outer membrane protein (Yop)-specific IgA antibodies by ELISA. The positive results of this latter assay were confirmed by immunoblot. Only one sample gave a positive agglutination reaction with Y. enterocolitica antigen (group 03) and four exhibited an equivocal reaction with Y. pseudotuberculosis antigens (groups II and IV). Contrary to the low incidence of agglutinins, 15.1% of the samples showed a positive Yop-specific IgA reaction, while further 5.3% samples fell into the equivocal range by ELISA (17 and 6 specimens, respectively). Eleven of these samples (9.8% of all specimens tested) were also positive by immunoblot for the presence of Yop-specific IgA antibodies. These data suggest a higher incidence of yersinia infections than the 1.0-1.4 per 10(5) population predicted on the basis of stool culture results.

How to substantiate eradication of bovine brucellosis when aspecific serological reactions occur in the course of brucellosis testing

Collaborative work was financed by the EU to develop and assess new diagnostic tools that can differentiate between bovine brucellosis and bovine infections due to Yersinia enterocolitica O:9 either in conjunction with, or as an alternative to, the classical serological, bacteriological or allergic skin tests. Sixteen heifers were experimentally infected with Brucella abortus biovar 1 (five heifers), Brucella suis biovar 2 (two heifers), Y. enterocolitica O:9 (six heifers) and Y. enterocolitica O:3 (three heifers). Four heifers, naturally infected with Y. enterocolitica O:9 that presented aspecific brucellosis serological reactions were also included in the experiment. A self-limited infection was induced in cattle by B. suis biovar 2. All the brucellosis serological tests used, i.e. the slow agglutination test (SAW), the Rose Bengal test (RB), the complement fixation test (CFT), indirect and competitive ELISA’s, lacked specificity when used to analyze sera from Y. enterocolitica O:9 infected animals. A Yersinia outer membrane proteins (YOPs)-ELISA was also used and although the test is able to detect a Yersinia group infection, it provided no evidence of whether or not there is a possible brucellosis infection when dual infections are present. The brucellergen IFN-γ test showed a lack of specificity also. The only test that was proven to be specific is the brucellergen skin test. All brucellosis serological tests, except the indirect ELISA, were limited in their ability to detect B. abortus persistently infected animals. Based on these experimental studies, a strategy was implemented as part of the year 2001 Belgian Brucellosis Eradication Program to substantiate the eradication of bovine brucellosis. Epidemiological inquiries have identified risk factors associated with aspecific serological reactions, possible transmission and infection of cattle by B. suis biovar 2 from infected wild boars; and both legal and administrative measures taken by the veterinary services. No cases of bovine brucellosis have been confirmed in Belgium since March 2000.

Effects of Yersinia enterocolitica O:3 derivatives on B lymphocyte activation in vivo.

The potential sequelae of intestinal infection with Yersinia enterocolitica include reactive arthritis, erythema nodosum, Reiter's syndrome and other autoimmune diseases. The role of the immune response in the pathogenesis of these diseases has not been fully defined, but autoimmune manifestations may be a consequence of the increase in autoantibodies as a result of polyclonal B-cell activation induced by Yersinia. We investigated the effects of Y. enterocolitica O:3 derivatives on B lymphocyte activation in vivo. Groups of five specific pathogen free (SPF) Swiss mice were inoculated with bacterial cell extract, Yersinia outermembrane proteins (Yops) or lipopolysaccharide (LPS) obtained from Y. enterocolitica O:3 and their immunoglobulin-secreting spleen cells were detected by isotype-specific protein A plaque assay. The presence of specific anti-Yersinia antibodies and autoantibodies was determined in mouse sera by ELISA. In all experiments a marked increase in the number of secretory cells of different isotypes was observed as early as the third day after inoculation. IgG and IgM anti-Yersinia antibodies were detected in the sera of all inoculated mice, and autoantibodies against myosin in the sera of those inoculated with bacterial cell extract. The sera from animals stimulated with LPS reacted with myelin, actin and laminin, while the sera from mice inoculated with Yops reacted with myelin, thyroglobulin and cardiolipin. These results suggest that SPF Swiss mice inoculated with any one of the Y. enterocolitica derivatives tested exhibited polyclonal activation of B lymphocytes as a result of stimulation by various bacterial components and not only LPS stimulation.