Kinetics study and characterisation of target excreted/secreted antigens of immunoglobulin G, M, A and E antibodies from mice infected with different strains of Toxoplasma gondii

A kinetics study and characterisation of target excreted/secreted antigens of immunoglobulin (Ig) G, M, A and E antibodies were realised by Western blotting with immune sera of mice inoculated with three strains of Toxoplasma gondii: RH, C56 and S3. IgG antibodies of the immune sera recognised the major proteins of the three excreted/secreted antigen preparations with molecular masses of 30, 45, 63 and 77 kDa. IgM antibodies recognised proteins revealed by IgG antibodies but with variable intensities; some proteins were revealed during a short period. IgA antibodies did not recognise the 35-kDa antigen or the antigens inferior to 28 kDa. The RH excreted/secreted antigens were revealed with the highest intensity. The IgE antibodies were briefly detected in trace amounts during period from the 20th to the 35th day. The RH strain with its excreted/secreted antigens had the best antigenicity and is a good model for immunoprotection studies.     

Factors associated with successful mobilization of peripheral blood progenitor cells in 200 patients with lymphoid malignancies

To examine the repertoire of Pneumocystis carinii antigens recognized by antibody-secreting B cells from tracheobronchial lymph nodes isolated immediately following recovery from P. carinii pneumonia, monoclonal antibodies (MAbs) were produced from these cells. In contrast to previous studies of systemic immunity, P. carinii gpA was not the immunodominant antigen recognized by these B cells. Forty-nine (91%) of 54 P. carinii-specific hybridoma culture supernatants reacted with P. carinii antigens other than gpA. Many of the resulting MAbs recognized a previously uncharacterized antigen expressed on the surface of both cysts and trophozoites. Western blotting using one of the cloned MAbs revealed reactivity with a broad range of antigenic material, with the most intense reactivity in the 50- to 65-kDa region of the blot. The antigens identified by these MAbs merit further investigation regarding protective immunity to P. carinii because they were recognized by B cells in the context of recovery from P. carinii pneumonia.     

Orthopedic and interventional applications at low field MRI with horizontally open configuration. A review

Two monoclonal antibodies (MAbs), designated as H9 (IgG2a) and H20 (IgM), directed against heat-shock protein 60 (HSP60) of Helicobacter pylori strain TK1029 were established. Affinity-purified antigens cross-reacted in immunoblots with MAb H9 and MAb H20 respectively. These antigens also reacted with the 3C8 MAb previously established in this laboratory, which recognised Yersinia enterocolitica HSP60. By amino-acid sequence analysis, the N-terminal amino-acid sequence of the protein recognised by both H9 and H20 MAbs was confirmed as the amino-acid sequence of H. pylori HSP60 reported previously. Both MAbs reacted with nine strains of H. pylori in enzyme-linked immunosorbent assay (ELISA) and immunoblot analysis. In addition, MAb H9 reacted with extracts of other bacteria including H. mustelae, Pseudomonas aeruginosa, Vibrio cholerae, Serratia marcescens, Proteus mirabilis, Escherichia coli and Shigella sonnei. In contrast, MAb H20 reacted only with strains H. pylori. These results suggest that both the species-specific epitope recognised by MAb H20 and the common epitope recognised by MAb H9 exist on HSP60 of the bacterial cell. Both MAbs also reacted with the 60-kDa protein in the lysate of human gastric carcinoma (MKN45) cells. It was shown by immunohistochemical staining that gastric epithelial cells of four out of six biopsy specimens examined stained positively with MAb H20. These results suggest that there is a common epitope in H. pylori HSP60 and human gastric epithelial cells.     

Severe case of pemphigoid gestationis with unusual target antigen

We report a severe case of pemphigoid gestationis (PG) with an unusual target antigen. The patient developed a severe itchy macular rash on the abdomen during her fifth pregnancy, at 38 weeks' gestation. The disease persisted for 8 months post-partum, and could only be controlled with high doses of systemic corticosteroids and dapsone. The diagnosis of PG was confirmed by direct and indirect immunofluorescence. A linear band of IgG and C3 was detected at the epidermal aspect of salt-split skin. Immunoblotting studies revealed circulating IgG antibodies binding to a single 200-kDa protein in epidermal extracts. Immunofluorescence studies using trypsinized human keratinocytes demonstrated uniform staining around the cell peripheries, suggesting that the target antigen was not associated with hemidesmosomes. These findings differ from the usual immunological features seen in PG, and suggest further heterogeneity of the antigens involved in PG.     

Lipoprotein profile, diet and body composition in athletes practicing mixed an anaerobic activities

To investigate the prevalence and possible role of anti-endothelial cell antibodies (AECA) in the pathogenesis of systemic lupus erythematosus (SLE), cell membrane antigen was prepared from cultured human umbilical vein endothelial cells and immunoblotting performed to detect AECA in SLE sera. IgG-AECA could be detected in 41 (86%) of 47 SLE patients. They were highly specific and failed to react with membrane antigens of human peripheral blood mononuclear cells or granulocytes. IgG-AECA reacted with endothelial membrane antigens which ranged from 15 to 200 kDa in molecular size. Further analysis of the antigens reacting with IgG-AECA revealed some interesting correlations between specific species of antibodies with certain clinical manifestations. Thus, patients having lupus nephritis, vasculitis, and hypocomplementemia had IgG-AECA against a 66-kDa membrane antigen; those with thrombocytopenia had IgG-AECA against a 55-kDa antigen; those with pleuritis had IgG-AECA against an 18-kDa antigen. These results indicate that IgG-AECA in the sera of SLE patients consist of heterogenous species.     

Long-term lipid-based total parenteral nutrition activates mononuclear cells and modulates membrane lipid composition in pigs

This study aims to assess the possible strain-dependent variations in detection of Toxoplasma antigens and antibodies. The virulent RH strain or avirulent Beverley strain of T. gondii were injected into mice, intraperitoneally, and their antigens, antibodies and parasites were identified from the blood or tissues; liver, brain and spleen by ELISA, Western blot and PCR. In mice infected with RH strain, circulating antigens and parasitemia were first detected from 2 days after infection, and Toxoplasma DNA were found in the blood, liver, brain and spleen from 3 days after infection. It was impossible to detect specific IgM and IgG antibodies to T. gondii, and any specific band was not found by Western blot. In mice infected with Beverley strain, circulating antigens were detected between day 10 and day 35. The Toxoplasma DNA was found in the blood and liver from day 15 until day 60, and in the brain from day 20. But Toxoplasma DNA in the spleen were mainly detected between day 10 and day 30. The IgM antibodies were first appeared on day 10 post-infection, and were noted obviously increased between day 15 and 25. The IgG antibodies were first detected on day 15, and showed progressively increased titers. The antibody binding bands were specific according to infection period. Sera from mice infected with Beverley strain reacted mainly with the antigen of 27.5-kDa and 32.5-kDa. In conclusion, mice infected with RH strain revealed Toxoplasma antigens strongly, but not antibodies. However, mice infected with Beverley strain revealed both the Toxoplasma antigens and antibodies. The present results showed that immune responses are different between avirulent and virulent T. gondii.     

Bivalency is required for anticapsular monoclonal antibodies to optimally suppress activation of the alternative complement pathway by the Cryptococcus neoformans capsule

Encapsulated cells of Cryptococcus neoformans are potent activators of the alternative complement pathway. Previous studies found that monoclonal antibodies (MAbs) specific for the major capsular polysaccharide, termed glucuronoxylomannan (GXM), can markedly suppress the ability of the capsule to accumulate C3 from normal human serum via the alternative pathway. The present study examined the abilities of F(ab)2 and Fab fragments of three MAbs (MAbs 439, 3C2, and 471) to mediate the suppressive effect. The results showed that F(ab)2 fragments of all three MAbs suppressed activation and binding of C3 via the alternative pathway in a manner similar to that of intact antibodies. In contrast, Fab fragments of MAb 439 and MAb 3C2 showed no suppressive activity, and Fab fragments of MAb 471 were markedly reduced in suppressive activity. Indeed, there was an earlier accumulation of C3 on encapsulated cryptococci in the presence of the Fab fragments. Study of subclass switch families of MAb 439 and MAb 471 found that MAbs of an immunoglobulin G (IgG) subclass with increased flexibility in the hinge region (IgG2b) had less suppressive activity than MAbs of IgG subclasses with less flexibility (IgG1 or IgG2a). Taken together, these results indicate that cross-linking of the capsular matrix is an essential component in suppression of the alternative complement pathway by anti-GXM MAbs.     

Human preformed IgG combining with membrane-bound porcine serotransferrin lyse porcine endothelial cells through antibody-dependent cellular cytotoxicity

Preformed antibodies are involved in xenograft rejection. The purpose of this work was to characterize porcine xenoantigens recognized by human preformed IgG (hpIgG), and to investigate the role of hpIgG in xenogeneic rejection. IgG eluted from porcine livers perfused with human plasma, human sera and total human IgG were immunoblotted on porcine aortic endothelial cell extracts. The amino acid sequence of a 76-kDa antigen constantly revealed was 100% homologous with porcine serotransferrin (psTf). hpIgG from human sera, human IgG1 and IgG2 and F(ab')2gamma specifically bound to psTf. Neutralization by psTf abolished that binding. Although alpha1,3-linked galactose residues (Gal(alpha)1,3Gal) is the dominant epitope recognized by preformed antibodies in the swine-to-human combination, the analysis of carbohydrate composition of psTf showed that the molecule was devoid of Gal(alpha)1,3Gal moieties and that preformed anti-psTf IgG bound to epitopes localized on the peptide core of the molecule. Purified human anti-psTf IgG antibodies were able to bind to psTf linked to its receptor on porcine endothelial cells, and to kill those cells through antibody-dependent cellular cytotoxicity.     

Characterization of the neutrophil molecules identified by quinine-dependent antibodies from two patients

BACKGROUND: Two patients with episodic pancytopenia and renal failure associated with quinine (Qn) ingestion were previously found to have Qn-dependent antibodies that reacted with red cells, platelets, and neutrophils. The purpose of these studies was to characterize the neutrophil antigens recognized by Qn-dependent antibodies from these two patients. STUDY DESIGN AND METHODS: The neutrophil molecules recognized by the Qn-dependent antibodies in the sera from the two patients were analyzed by immunoprecipitation using 125I-labeled neutrophils. Neutrophils from 13 different donors were tested. RESULTS: The Qn-dependent antibodies from Patient 1 immunoprecipitated a 60-kDa molecule on neutrophils from seven donors and an 85-kDa molecule on neutrophils from three donors. The Qn-dependent antibodies from Patient 2 reacted with a 32-kDa molecule on neutrophils from 5 donors, a 60-kDa molecule on neutrophils from 9 donors, and an 85-kDa molecule on neutrophils from 10 donors. Neutrophil-specific antigen NB1 is also located on a 60-kDa glycoprotein (GP). While the antibody in serum from Patient 1 did not show specificity for NB1, the antibody from Patient 2 detected the 60-kDa molecule on NB1-positive neutrophils from 9 of 11 donors tested and did not detect the 60-kDa molecule on NB1-negative neutrophils from 2 donors. In a monoclonal antibody immobilization of granulocyte antigens assay, the Qn-dependent antibody from both patients reacted with the 60-kDa molecule carrying NB1. The Qn-dependent antibody from a third patient, Patient 3, was previously found to react with an 85-kDa GP and the 60-kDa NB1 GP. To determine if the Qn-dependent antibodies from Patients 2 and 3 recognized the same 85-kDa GP, neutrophils were treated with serum from Patient 3 plus Qn to remove the 85-kDa GP. Then, serum from Patient 2 plus Qn no longer immunoprecipitated the 85-kDa GP. CONCLUSION: The antigens recognized by Qn-dependent neutrophil antibodies were located on molecules of 85, 60, and 32 kDa. Qn-dependent antibodies from two patients reacted with the same 85-kDa GP and those from three patients reacted with the same 60-kDa GP. The 60-kDa molecule recognized by the Qn-dependent antibodies carried the NB1 antigen.     

Identification of intermediately virulent Rhodococcus equi isolates from pigs

We recently reported the existence of Rhodococcus equi isolates with at least three virulence levels, isolated from AIDS patients: virulent R. equi having 15- to 17-kDa antigens that kills mice with 10(6) cells, intermediately virulent R. equi having a 20-kDa antigen that kills mice with 10(7) cells, and avirulent R. equi that does not kill mice with 10(8) cells or more (S. Takai, Y. Imai, N. Fukunaga, Y. Uchida, K. Kamisawa, Y. Sasaki, S. Tsubaki, and T. Sekizaki, J. Infect. Dis. 172:1306-1311, 1995). Virulent R. equi having the 15- to 17-kDa antigens has been isolated frequently from horses and their environment, but the source of intermediately virulent R. equi having the 20-kDa antigen is poorly understood. There are many reports of the isolation of R. equi from the lymph nodes of pigs with and without lesions resembling those of tuberculosis. Therefore, we analyzed antigens of R. equi isolates from the submaxillary lymph nodes of pigs by immunoblotting with monoclonal antibodies against these virulence-associated antigens. Immunoblots of whole-cell antigen preparations of R. equi pig isolates revealed the presence of the 20-kDa antigen in almost all the pig isolates studied, and these isolates were intermediately virulent for mice. We also demonstrated that the expression of the 20-kDa antigen and its pathogenicity in mice were associated strongly with the presence of five large, distinct plasmids of 70 to 95 kb; two of the five plasmids from pig isolates were the same sizes as those from human isolates. These results suggest that R. equi having the 20-kDa antigen exists in the submaxillary lymph nodes of pigs and that the source of infection in some human cases might be associated with pigs and their environment.     

A comparison of fluvoxamine and fluoxetine in the treatment of major depression

Two monoclonal antibodies (MAbs) to human placenta laminin (pl-LAM), 1D8 (IgG1) and 6G5 (IgG2b) were generated and shown by ELISA and immunoblot analysis to recognize only native pl-LAM, but not denatured, reduced pl-LAM or mouse EHS laminin. Intact pl-LAM was easily isolated and purified in large scale from human placenta by 1D8-conjugated affinity chromatography. Electrophoretic analysis of the purified pl-LAM revealed the presence of a major 750-kDa component composed of 320-, 220-, and 200-kDa polypeptides and a minor 800-kDa component composed of 320-, 240-, and 220-kDa polypeptides. Neither molecule had a 400-kDa component corresponding to the A chain. It has already been shown that the 320-kDa polypeptide is identical to the M chain of human merosin (Hori et al. J. Biochem. 1994;116:1212-1219). Electron microscopy revealed that isolated merosin was composed of three short arms and one long arm. By immunohistochemistry, MAbs showed positive staining in human adult kidney and liver. These results indicate that these MAbs recognize only native merosin and can be used to study merosin structure and function by rapid purification of native merosin and by immunohistochemical analysis.     

Primary infection of dogs with Echinococcus granulosus: systemic and local (Peyer's patches) immune responses

Local and systemic lymphocyte proliferation and antibody production were tested in five dogs 35 days after primary experimental infection with Echinococcus granulosus. A significant cell proliferation was demonstrated by [3H] thymidine incorporation in mesenteric, popliteal and/or Peyer's patches (PPs) cells in response to E. granulosus protoscolex or adult worm antigen in three of five infected dogs, but not in five control animals. In contrast, blood mononuclear cells responded very weakly in only two of the infected dogs to parasite antigens. Elevated levels (compared with preinfection status) of protoscolex- and adult worm antigen-specific serum IgG were detected (ELISA) in four of the five dogs 35 days after infection. Furthermore, slightly elevated levels of parasite-specific IgE and IgA were observed in the sera of three and four in four infected dogs, respectively. Specific serum IgM was not significantly higher 35 days after infection than before infection. Local antibody production was studied in vitro using PPs, mesenteric and popliteal cells isolated from three infected and three uninfected dogs by ELISA using adult worm antigen. In two of three cultures of unstimulated PPs cells of infected dogs, parasite-specific IgG was detectable. Parasite-specific IgA and IgM were detected in one of the unstimulated PPs cell culture derived from an infected dog. Following in vitro stimulation with parasite antigen, PPs cells from two infected dogs showed increased parasite-specific IgG and PPs cells of all three infected dogs produced parasite-specific IgA. PPs cells from uninfected dogs did not produce significant quantities of parasite-specific antibodies and cells from mesenteric and popliteal lymph nodes of infected or uninfected dogs neither produced antibodies whilst in in vitro cultures.     

Allopurinol reduces bacterial translocation, intestinal mucosal lipid peroxidation, and neutrophil-derived myeloperoxidase activity in chronic portal hypertensive and common bile duct-ligated growing rats

The Chinese population in Hong Kong has a low incidence of invasive Haemophilus influenzae type b(Hib) disease, as well as carriage of the microorganism. Likely stimuli for the natural antibodies to Hib, which might protect against Hib infection, are cross-reactive antigens of bacteria like Escherichia coli K 100. Our aim was to determine the isotype and idiotype distribution and cross-reactivity of natural antibodies against Hib capsular polysaccharide (CP) in healthy Hong Kong Chinese. Titration of 20 sera by ELISA showed IgG antibodies reacting with Hib CP in all individuals. The antibodies were mainly IgG2, and their avidity index ranged widely. Isoelectric focusing (IEF) combined with immunoblotting showed patterns of IgG2 antibody clones against the CP of Hib and E. coli K 100 which were similar in 10 cases. Absorption with Hib CP only eliminated some bands in two sera. Absorption with K 100 CP did not remove any anti-Hib CP bands. In three sera additional clones of antibodies reacting to K 100 CP only, disappeared after absorption with this CP. Spectrotypic analyses of IgG antibodies reacting with anti-Hib idiotype 1 (Id-1) revealed stronger IEF patterns with bands in differing locations compared with anti-Hib CP antibodies. The strong reactivity of serum IgG, IgA and IgM antibodies with monoclonal anti-Hib Id-1 was confirmed by ELISA. This reactivity was not abolished after absorption of the sera with either Hib CP, or K 100 CP. The data indicate a high prevalence of Id-1 among Hong Kong Chinese. However, only one individual had Id-1 antibodies specific for Hib CP, judging from absorption experiments. Others had much lower activity of Id-1 anti-Hib CP antibodies compared with the total IgG Id-1, suggesting that Hong Kong subjects have Id-1-positive antibodies in their serum which are not specific for Hib CP. This is consistent with the nature of Id-1, which is a marker of A2VL region usage rather than a marker of a Hib CP paratope. We suggest that natural antibodies reacting with Hib CP in healthy Hong Kong Chinese are the product of exposure to some cross-reactive antigen(s), different from both Hib and E. coli K 100 CP.     

Activity of placental glutathione peroxidase and superoxide dismutase in cows with and without retained fetal membranes

We recently reported that there are two different virulence-associated antigens correlated with virulence levels in Rhodococcus equi isolates from AIDS patients: virulent R. equi that kills mice with 10(6) cells expresses 15- to 17-kDa antigens and intermediately virulent R. equi that kills mice with 10(7) cells expresses a 20-kDa antigen. Environmental parameters were evaluated for their effects on the expression of these virulence-associated antigens in virulent R. equi strains by immunoblotting using monoclonal antibodies in this study. Expression of these two virulence-associated antigens of R. equi was regulated by pH and temperature; the antigens were produced maximally when the isolates were grown at 38 C and pH 6.5, but were not produced when grown at 38 C and pH 8, nor at temperatures below 30 C. The 20-kDa antigen was found to be located on the cell surface, as were the 15- to 17-kDa antigens, and showed susceptibility to proteolysis by trypsin. These results indicate that expression of the virulence-associated antigens of R. equi is dependent on the environmental conditions.     

Rapid detection of a Schistosoma mansoni circulating antigen excreted in urine of infected individuals by using a monoclonal antibody

Schistosoma circulating antigens were used to indicate the infection intensity and to assess cure. An immunoglobulin G2a (IgG2a) mouse monoclonal antibody was used in a fast dot-enzyme-linked immunosorbent assay (ELISA; FDA) for rapid and simple diagnosis of schistosomiasis in the field. Seven hundred Egyptians were parasitologically examined for Schistosoma mansoni and other parasitic infections. A rectal biopsy was done as a "gold standard" for individuals showing no S. mansoni eggs in their feces. Egg counts were obtained by the Kato smear method for only 100 of 152 individuals with eggs in their feces. Specific anti-schistosome IgG antibodies were evaluated in sera by ELISA. Urine samples from the 700 individuals were tested by FDA for detection of the circulating antigen. The assay showed a sensitivity of 93% among 433 infected individuals and a specificity of 89% among 267 noninfected individuals. FDA showed the highest efficiency of antigen detection (91%) compared with the efficiency of antibody detection by ELISA (75%) and stool analysis (60%). In addition, FDA detected infected patients with 20 eggs/g of feces. Also, the sensitivity of FDA ranged from 90 to 94% among samples from patients with different clinical stages of schistosomiasis. All the assay steps can be completed within 30 min at room temperature for 96 urine samples. The monoclonal antibody identified a 74-kDa antigen in different antigenic extracts of S. mansoni and Schistosoma haematobium and in the urine of infected individuals. In addition, a 30-kDa degradation product was identified only in the urine samples. On the basis of these results, FDA should be used as a rapid tool for the sensitive and specific diagnosis of Schistosoma infection.     

Comparison of cardiac findings at necropsy in octogenarians, nonagenarians, and centenarians

The Toxoplasma gondii rhoptry protein Rop2 was expressed in Escherichia coli as a fusion protein containing 44 kDa of the 55-kDa mature Rop2, supplied with six histidyl residues at the N-terminal end (Rop2196-561). Humoral response during Toxoplasma infection of humans was analyzed by immunoglobulin G (IgG), IgA, and IgM enzyme-linked immunosorbent assay with Rop2196-561 as the antigen substrate. The analyzed sera were divided according to T. gondii-specific serological tests (IgG, IgA, or IgM indirect immunofluorescence and IgA or IgM immunosorbent agglutination assay) as group A (IgG+ IgA- IgM-; n = 35), group B (IgG+ IgA+ IgM+; n = 21), group C (IgG+ IgA+ IgM-; n = 5), and group D (IgG+ IgA- IgM+; n = 16). Twenty-six T. gondii-seronegative sera from individuals with other infections were also included (group E). Anti-Rop2 IgG antibodies were detected in 82.8% of group A sera and in 97.6% of the sera with acute-phase marker immunoglobulins (groups B, C, and D). The percentage of IgA antibody reactivity against Rop2196-561 was 17.1% in group A, 50% in group D, and 80.8% in groups B and C. The percentage of IgM antibody reactivity was 0% in groups A and C and 62% in groups B and D. Sera from group E failed to show IgA, IgM, or IgG antibody reactivity. Since T. gondii Rop2 elicits a strong humoral response from an early stage of infection, it is suggested that recombinant Rop2196-561 would be suitable for use in diagnostic systems, in combination with other T. gondii antigens, to detect specific IgG, IgA, and IgM antibodies.     

Isotype-specific immune responses in murine experimental anisakiasis

A murine experimental model of anisakiasis has been developed in BALB/c and C57BL/10 mice orally inoculated with an Anisakis simplex living third stage larva (L3) in order to investigate isotype-specific immune responses against excretory-secretory (ES) products and crude extracts (CE) from L3. Specific antibody production showed similar patterns against both ES and CE antigens with higher levels against the latter. The dynamics of the production showed the earliest responses in BALB/c, in which antibodies were principally of the immunoglobulin (Ig)M isotype. Responses to the IgG1 subclass were mainly produced in the C57BL/10 strain. Levels of IgG2a were practically undetectable. With sera from C57BL/10 mice high levels of the IgG2b isotype were detected. A slight IgG3 response was only detected against the CE antigen in the C57BL/10 strain by the end of the experiment and IgA responses were very low. Humoral responses against A. simplex antigens are different depending on individual characteristics and thymus-independent epitopes might be represented into A. simplex antigens and their stimuli could be different regarding the murine strain used.     

An indirect radioimmunoassay for thymus leukemia (TL) antigens

An indirect radioimmunassay for thymus leukemia (TL)2 antigens has been developed and its specificity documented. The assay makes use of anti-TL antibodies produced in congenic mice (A-Tla(b)) and radioiodinated purified rabbit anti-mouse IgG. Using this assay, differences can be detected in the amounts of antigen expressed on thymocytes of the three known phenotypes (TL.1,2,3;TL.2;TL-) of inbred mouse strains. Significant differences are also detected in comparison of the thymocytes from homozygous TL.1,2,3 mice (A-Tla(a)) and heterozyhotes from Tla(a) and Tla(b) parents. Optimum conditions for the assay have been established. Its ability to detect antigens on glutaraldehyde-fixed cells and the binding of noncytolytic antibodies on both viable and fixed cells are documented. The assay has also been used to quantitate the changes in TL antigen expression on cells incubated in anti-TL antisera under conditions of antigenic modulation.     

Escherichia coli strains with nonimmune immunoglobulin-binding activity

We have identified several strains of Escherichia coli which contain immunoglobulin-binding activity on the cell surface. Affinity-purified antibodies ordinarily used as secondary antibodies in immunodetection protocols were bound by 6 of 72 strains of the ECOR reference collection of E. coli. The Fc fragments of both human and sheep immunoglobulin G (IgG) were also bound, demonstrating the nonimmune nature of the phenomenon. Binding of conjugated IgG Fc directly to unfixed cells was observed by fluorescence microscopy. Western blots showed that the immunoglobulin-binding material occurs in the form of multiple bands, with the apparent molecular masses of the most prominent bands exceeding 100 kDa. No two of the strains have the same pattern of bands. The binding activity in extracts was sensitive to proteinase K. The binding activity of intact cells was reduced preferentially by trypsin digestion, demonstrating exposure at the cell surface. Expression of binding activity in Luria-Bertani broth cultures was favored by a temperature of 37 degrees C and entry into stationary phase of growth.