Comparison of molecular and immunological typing of isolates of Rice yellow mottle virus.

Isolates of Rice yellow mottle virus (RYMV) were typed at the molecular level through the sequences of the open reading frame (ORF) 4 (coding for the coat protein) and ORF1 (coding for the movement protein), and serologically by means of polyclonal and monoclonal antibodies. The overall patterns of diversity shown by molecular and serological analyses were similar: East-African isolates differed from West-African ones, and the West-African isolates from forest differed from the savannah ones. Each major strain had a different serological profile. However, molecular typing was more discriminating than immunological typing since several sequence variants belonged to the same serotype. In rare instances, there were explainable discrepancies between molecular and serological typing. Two amino acids at positions 115 (alanine vs threonine) and 191 (valine vs threonine) consistently discriminated between the major serotypes. These positions were located in antigenic sites as revealed by Spot-scan method and were recognised by discriminating monoclonal antibodies. One shared epitope, lying within a conserved region, may be responsible for the cross-reactivity between RYMV isolates. A rationale for the correlation between molecular and immunological typing of RYMV and other sobemoviruses is proposed.

Delineation of a neutralizing subregion within the immunodominant epitope (GH loop) of foot-and-mouth disease virus VP1 which does not contain the RGD motif.

The major immunogenic site of foot-and-mouth disease virus (FMDV) is contained in a disordered loop comprising residues 134-158 of capsid protein VP1, located on the surface of the viral particle. Peptides corresponding to this sequence generally elicit protective levels of neutralizing antibodies in guinea pigs. In some instances, however, the level of neutralizing antibodies is low although the level of antibodies against the peptide, determined by ELISA, is as high as that in the sera with high neutralizing antibody titres. In an attempt to ascertain the reason for this difference, we have synthesized on a cellulose membrane 10 overlapping decapeptides, offset by one residue, covering the segment 141-159 of VP1 of two viruses belonging to serotypes A12 and O1, and tested them with guinea pig antisera raised against peptide 141-159, VP1 and FMDV particles (SPOTscan method). With type A, some peptides which were strongly positive with highly neutralizing antisera did not include the RGD triplet located at residues 145-147. In contrast, antisera with low neutralization titres reacted only with decapeptides which included the RGD motif. Moreover, peptide 147-156 coupled to keyhole limpet haemocyanin, but not peptide 141-149 coupled to the same carrier, elicited high levels of neutralizing antibodies in guinea pigs. In the case of serotype O, highly neutralizing antisera to virus reacted in ELISA with peptides 141-150 (containing the RGD motif) and 135-144 (located upstream from the RGD motif). The results suggest that the RGD triplet is not an indispensable constituent of peptides able to elicit a neutralizing antibody response against the virus.

Comparison of two different methods using overlapping synthetic peptides for localizing linear B cell epitopes in the U1 snRNP-C autoantigen.

We have compared the performances of two different approaches using overlapping synthetic peptides to identify the location of linear epitopes of the U1 snRNP-C autoantigen. The first method was based on the use of 15 overlapping peptides (16-30 residue-long) synthesized using conventional Fmoc chemistry, removed from the resin by a standard cleavage procedure, and tested by ELISA after direct coating to polyvinyl microtiter plates. The second approach used a commercial kit (SPOT) to synthesize 75 overlapping decapeptides on cellulose membrane which were assayed by a direct immunoenzymatic test. Both standard and SPOTscan methods were evaluated with antibodies raised in rabbits against synthetic peptides of U1C and sera from patients with autoimmune diseases. In addition to inherent problems linked to the SPOT synthesis (in particular the impossibility of checking the quality of peptides), a number of limitations in the SPOTscan method were identified (e.g. a certain lack of sensitivity and, in one case, the complete lack of peptide reactivity due to the removal of charged end groups at both extremities). However, we found no background with sera from autoimmune patients in the SPOTscan and the antigenic maps obtained using the two approaches generally agreed. This study shows that the SPOTscan approach represents a simple, relatively non expensive and rapid method for initial screening to identify candidate sequences that may be dominant linear epitopes in a protein. Subsequent analysis and controls should include the preparation of conventionally synthesized peptides for formal immunochemical investigations.

Epitope peptides from interleukin-6 receptor which inhibit the growth of human myeloma cells.

A panel of monoclonal antibodies against the soluble IL-6 receptor was used to search for linear epitopes by a Pepscan analysis. Two such epitopes were found and the corresponding peptides were synthesized chemically. The peptides were active to inhibit the IL-6 dependent growth of human multiple myeloma cell line and the effect of IL-6 on growth of murine hybridoma cells. The epitope-defined, antagonist peptides reduced the transduction of the IL-6 signal which activates binding of Stat transcription factors to specific enhancers, but did not affect IL-6 binding. These effects were not seen with several other peptides from the IL-6 receptor sequence. A computer three-dimensional model of the IL-6 receptor complex was built and indicates that the antagonist peptides define one of the two possible sites of interaction between the domain-II of the IL-6 receptor molecule and that of the gp130 molecule within the hexameric receptor assembly.

Immune response related to the molecular structure of a peptide from the cholera toxin B subunit.

Three forms of a peptide P50-75 from the cholera toxin B subunit in the absence of carrier or adjuvant were administered orally or intraperitoneally to C57Bl/6J mice. Mice were given P50-75 as the free monomer, as an octamer synthesized on the seven polylysine core proposed by Tam (S), or as an octamer synthesized on the epsilon-amino groups of a chain of eight Lys-Gly-Gly units (C). P50-75, presented to the immune system, as monomer or polymers, generated similar serum titres of anti-cholera toxin (CT) antibodies. However, mice immunized orally with the polymers S and C were better protected against the intestinal effects of the toxin than mice immunized with the free monomer P50-75. S and C are more effective than P50-75 or the B subunit in increasing the amounts of total IgA secreted into the intestine and, moreover, the anti-CT IgA neutralized toxin activity. The amounts of anti-CT subclasses (IgG1, IgG2a, IgG2b, and IgG3 plus IgM) produced by the antigens depended on how the peptide P50-75 was presented for priming to the mice boosted thereafter with the B subunit.

Oral immunization with a synthetic peptide of cholera toxin B subunit. Obtention of neutralizing antibodies.

The ability of free synthetic fragments of the cholera toxin (CT), administered by parenteral or oral route, without adjuvant, to induce antibodies cross-reacting with CT was tested. Two peptides corresponding to the sequences 30-50 and 50-75 of the CT beta chain were selected and synthesized. Both free peptides, given intraperitoneally or orally, without adjuvant, elicited seric antibodies cross-reacting with CT. The anti-(P50-75) antibodies were able to neutralize the CT activity. Our results show that protection against a toxin at the systemic level can be obtained with a synthetic peptide even when administered by an oral route.

Solid phase synthesis of two cholera toxin B subunit antigens.

The 30-50 and 50-75 sequences of the cholera toxin beta chain including the amino-acids that are thought to be involved in toxin-receptor binding have been synthesized using the solid phase method. They were then purified by gel permeation and ion exchange chromatography. Both these free peptides induced serum antibodies recognising the native toxin after oral or intraperitoneal administration. Only the antibodies raised against the 50-75 peptide, however, were able to neutralize toxin activity.