Diagnosis of enteric fever by inhibition assay using peroxidase-labelled monoclonal antibody and Salmonella typhi lipopolysaccharide

The TUBEX test detects not only typhoid-specific antibodies but also soluble antigens and whole bacteria

TUBEX (IDL Biotech) is a 5 min semiquantitative colorimetric test for typhoid fever, a widely endemic disease. TUBEX detects anti-Salmonella O9 antibodies from a patient's serum by the ability of these antibodies to inhibit the binding between an indicator antibody-bound particle and a magnetic antigen-bound particle. Herein, we report that TUBEX could also be used to specifically detect soluble O9 lipopolysaccharide in antigen-spiked buffer by the ability of the antigen to inhibit the same binding between the particles. Sensitivity of antigen detection was improved (8-31 mug ml(-1)) by using a modified protocol in which the test sample was mixed with the indicator particles first, rather than with the magnetic particles as for antibody detection. The antigen was also detectable in spiked serum and urine samples, albeit less well (2-4-fold) than in buffer generally. However, no antigen was detected from six typhoid sera examined, all of which had anti-O9 antibodies. In addition, whole organisms of Salmonella Typhi (15 strains) and Salmonella Enteritidis (6 strains) (both O9(+) Salmonella), grown in simulated blood broths or on MacConkey agar, were also detectable by TUBEX when suspended at >9 x 10(8) organisms ml(-1). Expectedly, Salmonella Paratyphi A (7 strains), Salmonella Typhimurium (1 strain) and Escherichia coli (2 strains) were negative in the test. Thus, the same TUBEX kit may be used in several ways both serologically and microbiologically for the rapid diagnosis of typhoid fever. However, validation of the newer applications will require the systematic examination of real patient and laboratory materials.

One-step 2-minute test to detect typhoid-specific antibodies based on particle separation in tubes

Typhoid fever is caused by Salmonella typhi. Detection of anti-S. typhi antibodies in the patient is a useful diagnostic aid. Among the various methods developed over the years for this purpose, the Widal test, based on bacterial agglutination, has remained the most widely used, even though it is neither specific nor sensitive. Its popularity stems from the fact that it is simple to use and inexpensive. We describe a new test which also uses a simple one-step procedure but is more rapid and accurate than the Widal. The new test (TUBEX) detects anti-Salmonella O9 (both immunoglobulin M [IgM] and IgG) antibodies in patients by inhibiting the binding between an anti-O9 IgM monoclonal antibody (MAb) conjugated to colored latex particles and S. typhi lipopolysaccharide (LPS) conjugated to magnetic latex particles. The reactants are mixed in a specially designed microtube for 2 min, and the result is read based on the resultant color of the supernatant following forced sedimentation of the magnetic beads. In the absence of inhibitory antibodies, there is a color change (from blue to red) due to cosedimentation of the indicator particles with the magnetic particles, whereas if these antibodies are present, they prevent such a change to a degree dependent on their concentration. Preliminary examination of TUBEX using the anti-O9 MAb and irrelevant MAbs as inhibitors revealed the test to be specific and reproducible, with an analytical sensitivity of 16 micrograms per ml of antibody. The reagents remained stable for at least 9 months when kept at 4 degrees C. In the examination of 16 stored sera obtained from 14 patients with proven cases of typhoid fever and 78 serum samples from 75 subjects without typhoid fever, TUBEX was found to be 100% sensitive and 100% specific. The nontyphoid group comprised 26 healthy blood donors, 30 antinuclear antibody (ANA)-negative patients, 9 ANA-positive patients, of whom 1 was positive for anti-DNA antibody, 4 typhus patients, and 6 septicemic patients. In addition, the sera obtained from 11 patients clinically diagnosed as having typhoid fever were all positive in the test. The TUBEX results correlated to some extent, albeit insignificantly (r = 0.38, P = 0.07), with those of an enzyme-linked immunoassay (ELISA) which used a similar detection format (inhibition) and reagents (S. typhi LPS and anti-O9 antibody). TUBEX correlated very well with ELISAs which detected anti-S. typhi LPS IgM (r = 0.58, P = 0.003) or IgG (r = 0.54, P = 0.006) antibodies from the typhoid patients. There was no correlation with the Widal test. The TUBEX test, if performed on slides (instead of tubes) or with soluble antigen (instead of antigen-conjugated magnetic beads), suffered significantly in sensitivity. Direct agglutination tests using LPS-conjugated indicator particles performed either on slides or in microwells also failed to detect antibodies from the majority of typhoid patients. Thus, TUBEX appears to be well designed and well suited for use in the laboratory or by the bedside as a simple, rapid aid to the routine diagnosis of typhoid fever.

Trichinella spiralis: light microscope monoclonal antibody localization and immunochemical characterization of phosphorylcholine and other antigens in the muscle larva

A panel of monoclonal antibodies was used to examine the structure of the muscle larva of Trichinella spiralis under the light microscope. Immunofluorescence and, in some cases, immunoperoxidase staining were used. All four antibodies reacted with the cuticle of the organism, although differences in the staining pattern were observed for some of these. Interestingly, all the antibodies also reacted with the stichosome. One of the antibodies (Ts2Ab) is specific for the hapten, phosphorylcholine. In a binding assay, this antibody also reacted with extracts of Trichuris suis, Ascaris suum, and Fasciolopsis buski, but not with extracts derived from Cysticercus cellulosae, Candida albicans, Salmonella typhi, or Escherichia coli. This crossreactivity was confirmed microscopically in which the cuticle, oviduct and eggs of T. suis, the cuticle, muscle cells, and eggs of A. suum, and the cuticle and vitelline glands of F. buski were seen to be clearly stained by the antibody. In addition, Ts2Ab also reacted with the cuticle and stichosome of the adult T. spiralis worm. In Western blot analysis, Ts2Ab recognized a 43-kDa antigen from T. spiralis muscle larvae extracts, while a previously studied antibody (7C2C5Ab) identified four major antigens (48.5, 47, 43, and 39 kDa) in this preparation. Similar results were obtained when the 24-hr excretory-secretory (ES) antigens of T. spiralis were immunoblotted with the antibodies, although the reactivity shown by Ts2Ab was relatively weak. With the 72-hr ES material, on the other hand, major antigens of lower mol wt (44, 28, and 25 kDa) were revealed by 7C2C5Ab, and no reactivity was seen with Ts2Ab. However, this antigen preparation reacted well with both antibodies in an enzyme-linked immunoassay. Taken together, the findings suggest that the 72-hr ES antigens probably result from extensive degradation of material originally secreted or excreted by the worm. Similar binding studies on the 24-hr ES preparation indicated that this source may be relatively rich in 7C2C5Ab-reactive epitopes and relatively poor in the antigen identified by Ts2Ab. Other studies performed demonstrated that the antigens recognized by these two antibodies were distinct and physically unassociated.

A one-step two-particle latex immunoassay for the detection of Salmonella typhi endotoxin

A simple and rapid test (LIMM, short for latex immunoassay) is described for detecting Salmonella typhi endotoxin. It involves the simultaneous binding of the antigen by two types of reagent particles contained in a micro-tube: an indicator latex particle coated with a monoclonal antibody specific for the O-9 determinant on the endotoxin, and a magnetic bead coated with another monoclonal antibody specific for a different O-determinant. At the end of-the test, the magnetic beads are sedimented by use of a magnet, and the result is read based on the turbidity of the indicator latex suspension. Compared to a similar assay developed previously which uses only a single particle reagent (i.e., a tube agglutination system), LIMM was found to be slightly more sensitive especially when using short (less than 30 min) incubation times, and was at all times easier to read. The sensitivity of LIMM, in fact, increased with increasing time of incubation. When compared to the sensitivity (25 ng/ml) of a conventional slide latex agglutination test performed using the same indicator latex reagent, this parameter was 0-, 4.9-, 12.5- and 28.7-fold better after 5, 15, 30 and 60 min of incubation in the LIMM.

A two-particle turbidometric latex immunoassay for the detection of specific IgM antibodies

A simple two stage assay using latex particles as a reaction indicator has been developed for the detection of IgM antibodies to Trichinella spiralis. In the first stage, magnetic polystyrene beads (Dynabeads) coated with T. spiralis antigen were incubated for 30 min with the test serum. After washing, in the second stage, the assay was developed for 1 h using anti-mu-coated latex particles. After sedimentation of the Dynabeads the turbidity of the resultant latex suspension was measured spectrophotometrically at a wavelength of 400 nm. A decrease in turbidity of more than 20% from that of the control, unreacted, suspension was considered positive. Using an IgM phosphorylcholine-binding monoclonal antibody which was reactive with T. spiralis, the sensitivity of the assay was determined to be 110 ng/ml of antibody. This was 20-fold less than the sensitivity achieved in an indirect enzyme-linked immunosorbent assay (ELISA). When the assay was applied to sera obtained from CBA/N or BALB/c mice, which were either normal or immunized against T. spiralis, the expected results were obtained with titers up to 1/640 observed, and confirmed (r = 0.93, P less than 0.001) in the ELISA.

Monoclonal antibody-mediated, immunodiagnostic competitive enzyme-linked immunosorbent assay for equine monocytic ehrlichiosis

Competitive enzyme-linked immunosorbent assay (CELISA), mediated by a monoclonal antibody designated HybI, was developed for the diagnosis of equine monocytic ehrlichiosis. Inhibition of binding of HybI by the horse antibodies to Ehrlichia risticii was optimum at dilutions of 1:20 for serum and 1:10,000 for HybI. Mean optical densities (ODs) of positive and negative sera were 0.158 and 0.855, respectively. A comparison of ODs obtained by CELISA and indirect enzyme-linked immunosorbent assay (ELISA) indicated a marked tendency of positive and negative samples to cluster separately with respect to CELISA ODs, whereas the ELISA results displayed a continuum of ODs from negative to positive. Analysis of diagnosis by indirect fluorescent-antibody test (IFA), ELISA, and CELISA for 66 field-collected serum samples indicated that CELISA was superior to IFA and ELISA. Among 11 acute-phase serum samples negative by IFA which were obtained from horses that subsequently seroconverted, CELISA clearly demonstrated antibodies in 8 of these acute-phase sera, whereas 5 were borderline positive by ELISA. The presence of agent-specific humoral antibodies could be demonstrated conclusively by 14 days after infection. The results suggest that CELISA is more sensitive than IFA and ELISA and, owing to the marked differences between positive and negative samples, can be easily adapted for use in the field for detection of horse antibodies to E. risticii.

Monoclonal antibodies delineate multiple epitopes on the O antigens of Salmonella typhi lipopolysaccharide

Fifteen monoclonal antibodies (MAbs) directed against Salmonella typhi were produced and characterized. The specificities of the antibodies were determined by their binding patterns in an enzyme immunoassay, with a panel of lipopolysaccharides isolated from different bacteria. Seven MAbs reacted with S. typhi, Salmonella enteritidis, and Salmonella dublin (all belonging to serogroup D). One MAb also reacted with Salmonella paratyphi A and S. paratyphi B. Five MAbs reacted with S. typhi, S. enteritidis, S. dublin, and S. paratyphi B. Two MAbs did not bind to any lipopolysaccharide but showed reactivity with bacterial sonic extracts isolated from S. typhi, S. paratyphi A, S. paratyphi B, Escherichia coli, and Shigella sonnei. These antibodies would be helpful in studying the complexity of antigenic determinants expressed by S. typhi and the nature of the antibody response during typhoid and paratyphoid fevers and also in the diagnosis of the disease.

A comparison of immunological methods for the detection of Trichinella spiralis antigen

Eight immunological methods all using the same monoclonal antibody reagent were compared for the detection of Trichinella spiralis antigen. These were based on: (1) the direct adsorption of the antigen to the immunoadsorbent (nitrocellulose membrane, polyvinyl chloride strip or microplate); (2) capture of the antigen by antibodies pre-sensitized on the immunoadsorbent; and (3) latex agglutination. The methods found suitable were: (a) capture radioimmunoassay (capture-RIA) (sensitivity: less than 0.5 microgram/ml antigen); (b) direct enzyme immunoassay (direct-ELISA) (less than 0.5 microgram/ml); (c) tube latex agglutination test (2.2 micrograms/ml); and (d) direct immunodot assay (8.8 micrograms/ml). However, the performance of the direct-ELISA was greatly affected by the presence of each of three extraneous substances (bovine serum albumin (BSA), lipopolysaccharide (LPS), normal swine muscle homogenate (NSM) added to the antigen sample. The direct immunodot assay was also affected by the presence of BSA or LPS, whereas both the capture-RIA and the tube latex agglutination methods were affected by the presence of NSM only. The findings are discussed with a view of detecting T. spiralis larvae directly from pork samples by immunological means.

Detection of group D salmonellae in blood culture broth and of soluble antigen by tube agglutination using an O-9 monoclonal antibody latex conjugate

Latex particles sensitized with a Salmonella O-9 monoclonal antibody were used to detect group D salmonellae in blood culture broths. The system was found to be 100% accurate when used on 104 clinical specimens that included 13 S. typhi isolates. Enteric fever could thus be diagnosed as early as 1 day after the initiation of culture in some (18%) cases. The latex particles were also used in an experimental situation to detect soluble S. typhi lipopolysaccharide by a tube agglutination method. This was found to be more than four times as sensitive as the conventional slide agglutination method because at least 50 ng of antigen per ml in either buffer or urine was detected, albeit with less efficiency when serum was used.

Isolation of specific IgM monoclonal antibodies by affinity chromatography using alkaline buffers

Comparative studies on the efficacies of various buffers in eluting absorbent-bound antibodies revealed the denaturative effect of 3 M KSCN on all three IgM antibodies but not on an IgG protein, and the generally weak eluting power of glycine-HCl buffer, pH 2.5, on these monoclonal antibodies. A recently described medium consisting of 50% (v/v) ethylene glycol in an alkaline buffer, pH 10.5, was found to be relatively efficient for elution in all cases. However, subsequent studies on one of the IgM antibodies showed that alkali alone could effect elution, with recovery of active protein improving on increasing the pH, till the maximum (38%) at pH 11.0, after which denaturation occurred. Addition of ethylene glycol to the medium facilitated the elution; however, at pH greater than 10.0, the solvent potentiated the denaturative effect of the medium. Since pH 11.0 was found to be the highest pH in which all three IgM antibodies examined were stable, 0.1 M glycine-NaOH buffer, pH 11.0, may be a useful eluent for IgM (and other) antibodies in general.

Monoclonal IgM/A hybrid antibodies: artifacts due to anti-idiotype (T15) antibodies in commercial anti-alpha sera

A mouse hybridoma antibody, with specificity for Trichinella spiralis, was found to react against both anti-mu and anti-alpha sera obtained from two to three commercial sources. It also had a unique electrophoretic mobility, bound to staphylococcal protein A, and was comprised of a single type of heavy chain (mu-like) and light chain (kappa). However, Northern blot analysis of RNA extracted from the corresponding hybridoma cells revealed only mu but no alpha message. Subsequent studies on the protein, as well as on a similar "hybrid" antibody previously described, using antisera raised to the antibody but which had been absorbed against normal mu and alpha determinants, suggested an idiotype common to both antibodies: this was intuitively guessed, and later confirmed, to be the phosphorylcholine-specific T15 idiotype. It was further shown that anti-T15 antibodies prevailed in the commercial anti-alpha sera and these (rather than alpha-chain specific antibodies) were responsible for the cross-reactivities of the sera with the hybrid antibodies.

The antigenic structure of Toxoplasma gondii: a review

Even though T. gondii is ubiquitous in the animal kingdom, definitive information on its antigenic structure has only become available over the last few years, largely as a result of recent advances in immunology and biochemistry. New knowledge in this area will enable the immune response to the parasite to be studied in greater detail and may lead to the development of newer, more meaningful diagnostic tests for toxoplasmosis, and possibly a vaccine against it. This paper reviews knowledge on the antigenic structure of this extremely widespread and important protozoan parasite.