A novel approach to the laboratory diagnosis of Chlamydia trachomatis infections using monoclonal anti-idiotypic antibodies

Development of an ELISA using anti-idiotypic antibody for diagnosis of opisthorchiasis

Monoclonal antibody specific for an epitope of cretory-secretory antigen protein of Opisthorchis felineus (Rivolta, 1884) (Trematoda: Opisthorchiidae) with a molecular weight of 28 kDa was used in a sandwich enzyme-linked immunosorbent assay (ELISA) for immobilisation of liver fluke specific antigen to the solid phase. Examination of human sera by this ELISA compared with commercial assays demonstrated that the monoclonal antibody epitope is located within this significant parasite protein. Anti-idiotypic antibody specific for the paratope of this monoclonal antibody was obtained by a hybridoma technique. Mimicking an epitope of excretory-secretory antigen of O. felineus, it had the capacity to bind specific antibody and elicit an antibody response. The value of anti-idiotypic antibody as a substitute for the liver fluke antigen was tested by ELISA using serum samples of infected dogs. Anti-idiotypic antibody proved to be of value in both an indirect-ELISA and a competitive-ELISA for diagnosis of opisthorchiasis. Mature trematodes were isolated from all infected animals. The faecal egg counts were negative in dogs with a relatively small number of parasites, despite finding antibodies in serum by ELISA. Substitution of parasite antigen with anti-idiotype avoids the use of experimental animals and also reduces time-consuming steps of antigen preparation.

Use of a Guinea pig-specific transcriptome array for evaluation of protective immunity against genital chlamydial infection following intranasal vaccination in Guinea pigs

Guinea pigs have been used as a second animal model to validate putative anti-chlamydial vaccine candidates tested in mice. However, the lack of guinea pig-specific reagents has limited the utility of this animal model in Chlamydia sp. vaccine studies. Using a novel guinea pig-specific transcriptome array, we determined correlates of protection in guinea pigs vaccinated with Chlamydia caviae (C. caviae) via the intranasal route, previously reported by us and others to provide robust antigen specific immunity against subsequent intravaginal challenge. C. caviae vaccinated guinea pigs resolved genital infection by day 3 post challenge. In contrast, mock vaccinated animals continued to shed viable Chlamydia up to day 18 post challenge. Importantly, at day 80 post challenge, vaccinated guinea pigs experienced significantly reduced genital pathology - a sequelae of genital chlamydial infections, in comparison to mock vaccinated guinea pigs. Sera from vaccinated guinea pigs displayed antigen specific IgG responses and increased IgG1 and IgG2 titers capable of neutralizing GPIC in vitro. Th1-cellular/inflammatory immune genes and Th2-humoral associated genes were also found to be elevated in vaccinated guinea pigs at day 3 post-challenge and correlated with early clearance of the bacterium. Overall, this study provides the first evidence of guinea pig-specific genes involved in anti-chlamydial vaccination and illustrates the enhancement of the utility of this animal model in chlamydial pathogenesis.

Shark IgNAR antibody mimotopes target a murine immunoglobulin through extended CDR3 loop structures

Mimotopes mimic the three-dimensional topology of an antigen epitope, and are frequently recognized by antibodies with affinities comparable to those obtained for the original antibody-antigen interaction. Peptides and anti-idiotypic antibodies are two classes of protein mimotopes that mimic the topology (but not necessarily the sequence) of the parental antigen. In this study, we combine these two classes by selecting mimotopes based on single domain IgNAR antibodies, which display exceptionally long CDR3 loop regions (analogous to a constrained peptide library) presented in the context of an immunoglobulin framework with adjacent and supporting CDR1 loops. By screening an in vitro phage-display library of IgNAR variable domains (V(NAR)s) against the target antigen monoclonal antibody MAb5G8, we obtained four potential mimotopes. MAb5G8 targets a linear tripeptide epitope (AYP) in the flexible signal sequence of the Plasmodium falciparum Apical Membrane Antigen-1 (AMA1), and this or similar motifs were detected in the CDR loops of all four V(NAR)s. The V(NAR)s, 1-A-2, -7, -11, and -14, were demonstrated to bind specifically to this paratope by competition studies with an artificial peptide and all showed enhanced affinities (3-46 nM) compared to the parental antigen (175 nM). Crystallographic studies of recombinant proteins 1-A-7 and 1-A-11 showed that the SYP motifs on these V(NAR)s presented at the tip of the exposed CDR3 loops, ideally positioned within bulge-like structures to make contact with the MAb5G8 antibody. These loops, in particular in 1-A-11, were further stabilized by inter- and intra- loop disulphide bridges, hydrogen bonds, electrostatic interactions, and aromatic residue packing. We rationalize the higher affinity of the V(NAR)s compared to the parental antigen by suggesting that adjacent CDR1 and framework residues contribute to binding affinity, through interactions with other CDR regions on the antibody, though of course definitive support of this hypothesis will rely on co-crystallographic studies. Alternatively, the selection of mimotopes from a large (<4 x 10(8)) constrained library may have allowed selection of variants with even more favorable epitope topologies than present in the original antigenic structure, illustrating the power of in vivo selection of mimotopes from phage-displayed molecular libraries.

Characterization of the humoral immune response to Chlamydia outer membrane protein 2 in chlamydial infection

Detection of antibodies to an outer membrane protein 2 (OMP2) by enzyme-linked immunosorbent assay (ELISA) by using either the Chlamydia trachomatis- or the Chlamydia pneumoniae-specific protein was investigated. OMP2 is an immunodominant antigen giving rise to antibody responses in humans infected with different C. trachomatis serovars (A to C and D to K) or with C. pneumoniae, which could be detected by OMP2 ELISA. OMP2 ELISA is not species specific, but antibody titers were usually higher on the homologous protein. The sensitivity of this assay was high but varied according to the "gold standard" applied. Levels of antibody to C. pneumoniae OMP2 as detected by ELISA seem to return to background or near-background values within a shorter period of time compared to antibodies to C. pneumoniae detected by microimmunofluorescence (MIF), making it more likely that positive results in ELISA reflect recent infection. Thus, OMP2 ELISA has distinct advantages over MIF and commercially available ELISAs and might be a useful tool for the serodiagnosis of chlamydial infection.

Development of a diagnostic test for Entamoeba histolytica using idiotype expression in human

The protozoan parasite Entamoeba histolytica is the etiological agent of human amebiasis. The pathology of the disease starts with the cytolysis of the host target cells by amoebae. It is initiated by the adhesion of trophozoites to the host cells, through surface lectin via specific receptors. These adherence lectins have been demonstrated to be highly conserved, and can be recognised by serum antibodies from patients with invasive amebiasis. Some of these molecules have been used as antigens in serologic studies, which has been very helpful in the diagnosis of invasive intestinal amebiasis. However, false-positive serologic reactivity can occur using E. histolytica extracts and purified antigens. Additional problems are because the extracts display a great enzymatic activity. Several diagnostic methods, using different molecules and techniques, have been described. However, the problem still remains since these tests are not capable of differentiating between amoebic liver abscess (ALA) and intestinal amebiasis.Here, the research has been addressed to the 66-kDa antigen, which is a part of the outer membrane proteins from the E. histolytica strain HM1-IMSS trophozoites. First of all, we characterized the 66-kDa antigen in order to prove the relevance. We found that the 66-kDa antigen is a part of the plasma membranes and is distributed rather homogeneously on the cell surface of trophozoites. Apparently, the 66-kDa antigen is a glycoprotein. Using a monoclonal antibody (MAb), we found 25% of inhibition in the erythrophagocytosis by the trophozoites. Starting form one monoclonal antibody, we prepared an anti-idiotype (anti-Id) antibody reagent, with the purpose of searching for the different expressions of the idiotype between the sera from ALA and the intestinal amebiasis patients. Moreover, we produced the antibody Ab3 that is capable of recognising the 66-kDa antigen; it means that the Ab2 displays the internal image of the antigen. We found that 91.6% of the serum from ALA patients displayed the expression of the Id. In contrast, 15.7% of the E. histolytica asymtomatic cyst carriers displayed the Id expression, 6.6% of the patients with another parasite infection, and 11% of the negative controls (serum from umbilical cords of newborn babies). Our results showed that the expression of the Id could be differentiated among the AHA patients from the other groups with a 91.6% sensibility and 88.3% specificity.

Evidence that two distinct populations of rabbit anti-idiotypic antibodies are induced by three monoclonal antibodies specific for bluetongue virus core protein VP7

Three groups of anti-idiotypic antibodies (anti-Id or Ab2), designated RAb2-A, RAb2-B1, and RAb2-B2, were isolated from rabbit antiserum raised against three monoclonal antibodies (mAbs) (M1875, M1877, and M1886) specific for the bluetongue virus core protein, VP7. RAb2-A was specific for the idiotype of M1875. RAb2-B1 and RAb2-B2, isolated through the M1877 and M1886 affinity columns, respectively, were directed against the common idiotype that is shared by M1877 and M1886 and therefore classified in the same population (RAb2-B). Further characterization revealed that the two anti-Id populations, RAb2-A and RAb2-B, were significantly different. RAb2-A was an Ab2 beta type of anti-Id since (i) its reaction with M1875 was inhibited by the antigen; (ii) it inhibited the M1875-VP7 interaction; and (iii) it elicited anti-VP7 antibody response in Balb/c mice. In contrast, RAb2-B may represent an Ab2 alpha type of anti-Id since its reactions with M1877 or M1886 were not inhibited by the antigen, even though it inhibited mAbs from binding to the antigen. These results indicated that RAb2-A and RAb2-B represent two distinct populations of anti-Ids to anti-VP7 mAbs with similar epitope specificity.

Internal image rabbit anti-idiotypic antibody detects sheep antibodies to the bluetongue virus core protein VP7

BACKGROUND

Rabbit polyclonal anti-idiotypic antibodies (anti-Id) were generated against three murine monoclonal antibodies (MAbs) specific for the group-specific antigen VP7 of bluetongue virus (BTV) by the sequential immunization method. It was demonstrated by serological tests that part of the anti-Id possesses the characteristics of internal image anti-Id. By affinity purification against the individual MAbs, the internal image anti-Id, designated RAb2-A, was isolated and identified as specific for the MAb, M1875.

OBJECTIVES

To examine the ability of RAb2-A to detect sheep anti-VP7 antibodies by recognition of the common idiotype (Idx).

STUDY DESIGN

Affinity-purified RAb2-A IgG, along with VP7, was applied on the solid-phase of ELISA plate and the membrane for Western blot analysis to detect anti-VP7 antibodies from sheep that were immunized with VP7 or were experimentally infected with BTV. An inhibition ELISA was employed to determine whether sheep anti-VP7 and M1875 recognize the same or similar epitope(s).

RESULTS

RAb2-A recognised the Idx on anti-VP7 antibodies from sheep that were either immunized with VP7 or experimentally infected with BTV. Specificity of the reaction was confirmed by the observation that RAb2-A did not react with normal sheep serum or sheep antibodies against epizootic haemorrhagic disease of deer virus, a bluetongue-related disease virus in the Orbivirus genus.

CONCLUSION

The ability of RAb2-A to detect anti-VP7 antibodies through recognition of the Idx suggests that RAb2-A can be used as a probe to detect anti-BTV antibodies.