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Biomedical subjects

M H Van Regenmortel

Publications and source records attributed to M H Van Regenmortel.

At least 19 recordsLinked to original sources
PubMed2001

Pitfalls of reductionism in the design of peptide-based vaccines.

It is widely believed that all biological phenomena can be reduced to chemistry and physics. Such a reductionist view disregards the fact that complex biological systems have relational (also called emergent) properties that their constituents lack and that cannot be deduced or predicted from the properties of the isolated components. When the individual components of the immune system are studied in isolation, many interconnections are lost and it is not possible to understand how the system functions at the level of the organism as a whole. Our increasing knowledge of the antigenic structure of viral proteins has also been of little help for improving the immunogenicity of individual viral epitopes and for enhancing their capacity to elicit a protective immune response against viral infection. When molecular design principles are used to optimize the binding properties of a synthetic peptide epitope with respect to one neutralizing monoclonal antibody, this does not ensure that the peptide, when used as immunogen, will be able to induce neutralizing antibodies that protect against disease. A reductionist approach does not provide the information required for designing peptide immunogens that will elicit neutralizing rather than non-neutralizing antibody responses.

Animals↗
PubMed2001

Analysing structure-function relationships with biosensors.

Elucidating the nature of the relationship between the structure and function of biomolecules remains one of the major challenges in biology. Biomolecules are dynamic entities that possess a variety of structures, and their functions at the molecular, cellular and organismic levels are quite different. Since there is no single causal link between structure and function, the search should be for correlations rather than causal relations. Biosensor instruments based on surface plasmon resonance are widely used for establishing correlations between the chemical structure of binding sites and their binding activity. Mutagenesis studies have shown that only a small percentage of the residues located in a binding site contribute to the binding energy. Since substitutions in residues located far away from the binding site are able to affect binding activity, this greatly complicates the rational design of proteins endowed with improved functions. However, biosensors can be used to determine and predict the influence of the chemical environment and of the structure of a ligand on binding kinetics.

Binding Sites↗
PubMed2001

Differential recognition of epitopes present on monomeric and oligomeric forms of gp160 glycoprotein of human immunodeficiency virus type 1 by human monoclonal antibodies.

The mechanism of infectivity neutralization of human immunodeficiency virus type 1 (HIV-1) by Ig is poorly understood. Three human monoclonal antibodies (mAbs 1b12, 2G12 and 2F5) that are able to neutralize primary isolates of HIV-1 in vitro have been shown to act synergistically. In the present study this synergy was analyzed by measuring the epitope accessibility and binding kinetics for these three mAbs with respect to monomeric and oligomeric env protein gp160 IIIB using surface plasmon resonance. The results indicate that oligomerization of gp160 affects the accessibility of some of the epitopes recognized by the mAbs and provide some insight into the mechanism of synergy between different anti-(HIV-1) mAbs.

Antibodies, Monoclonal↗
PubMed2001

Recognition of peptides by antibodies and investigations of affinity using biosensor technology.

The study of peptide-antibody interactions has many applications in biology and medicine. Synthetic peptides corresponding to single protein epitopes are used instead of intact proteins as reagents for the diagnosis of viral and autoimmune diseases. Furthermore, antibodies raised against peptides are useful reagents for isolating and characterizing gene products. In this review, methods for analysing the molecular basis of peptide-antibody interactions are described, such as amino acid replacement studies, X-ray crystallography of peptide-antibody complexes and biosensor technology based on surface plasmon resonance. The importance of peptide conformation in antibody recognition is discussed, and the antigenic reactivity of epitopes in synthetic peptides and in cognate, intact proteins is compared.

Amino Acid Sequence↗
PubMed2000

Binding measurements as surrogate biological assays: surface plasmon resonance biosensors for characterizing vaccine components.

There is considerable interest in the possibility of using surrogate physico-chemical assays for the quality control of vaccine components. Since biological activity always depends on a first binding step, the primary criterion for assessing biological activity is the ability of a vaccine component to bind specifically in a binding assay. Biosensor instruments that measure binding kinetics with considerable ease and precision are used increasingly to assess the quality of antigens intended for vaccination as well as the binding affinity of antibodies elicited by vaccination. The most widely used biosensor instrument is the BIACORE and its mode of operation is briefly described. The use of biosensors for measuring the active concentration of biomolecules and for assessing the probable effectiveness of vaccine-induced antibodies is described.

Biological Assay↗
PubMed1999

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.

Amino Acid Sequence↗
PubMed1999

Protection of swine from foot-and-mouth disease with one dose of an all-D retro peptide.

Nine pigs were given a single inoculum of 100 microg of the all-D retro peptide corresponding to the immunodominant GH loop encompassing residues 141-159 of capsid protein VP1 of foot-and-mouth disease virus serotype A, sub-type 12. The peptide was conjugated to activated keyhole limpet haemocyanin and oil-adjuvanted before inoculation. The animals were challenged eleven weeks post-vaccination by exposing them to a pig which had been infected with the virus by inoculation. Two naive animals were included in the challenge study as controls. One of the vaccinated animals was completely unprotected and two developed very small lesions. None of the six remaining animals exhibited any clinical signs but two developed antibodies against nonstructural proteins indicating that replication of the virus had occurred. No evidence of replication could be detected in the remaining four animals, either by rise in neutralizing antibody titre or by production of antibodies against non-structural proteins specific for virus replication.

Animals↗
PubMed1999

The antigenicity of tobacco mosaic virus.

The antigenic properties of the tobacco mosaic virus (TMV) have been studied extensively for more than 50 years. Distinct antigenic determinants called neotopes and cryptotopes have been identified at the surface of intact virions and dissociated coat protein subunits, respectively, indicating that the quaternary structure of the virus influences the antigenic properties. A correlation has been found to exist between the location of seven to ten residue-long continuous epitopes in the TMV coat protein and the degree of segmental mobility along the polypeptide chain. Immunoelectron microscopy, using antibodies specific for the bottom surface of the protein subunit, showed that these antibodies reacted with both ends of the stacked-disk aggregates of viral protein. This finding indicates that the stacked disks are bipolar and cannot be converted directly into helical viral rods as has been previously assumed. TMV epitopes have been mapped at the surface of coat protein subunits using biosensor technology. The ability of certain monoclonal antibodies to block the cotranslational disassembly of virions during the infection process was found to be linked to the precise location of their complementary epitopes and not to their binding affinity. Such blocking antibodies, which act by sterically preventing the interaction between virions and ribosomes may, when expressed in plants, be useful for controlling virus infection.

Antibodies, Viral↗
PubMed1999

Kinetics of interaction between 3-hydroxyphthaloyl-beta-lactoglobulin and CD4 molecules.

Kinetics of 3-hydroxyphthaloyl-beta-lactoglobulin-CD4 interaction were evaluated using a biosensor instrument based on surface plasmon resonance. A very fast association (k(a)=2.4+/-0.3x10(6)M(-1)s(-1)) and slow dissociation (K(d)=2.3+/-0.14x10(-4)s(-1)) rate constants were observed indicating the high affinity of the complex. This result together with earlier data, suggest that "structure-specific" requirements must be met to endow acid anhydride modified lactoglobulin with the capacity for high affinity binding to CD4.

Animals↗
PubMed1998

From absolute to exquisite specificity. Reflections on the fuzzy nature of species, specificity and antigenic sites.

The term specificity is derived from the word species and shares with it an inherent fuzziness based on the absence of sharp boundaries between closely related entities. Antibody specificity is a ternary relational property which refers to the antibody's capacity to discriminate between two or more epitopes. There are no sharp boundaries between the individual overlapping epitopes that constitute an antigenic site and there is also no clear-cut minimum difference in binding affinity or in atomic positions at the epitope-paratope interface that can serve as a yardstick for deciding that two epitopes or two paratopes are the same or not. Immunology shares with the whole of empirical science the need to handle fuzzy sets and concepts and this poses no threat to the unabated further development of immunochemical analysis.

Antibody Specificity↗
PubMed1998

Measurement of antigen-antibody interactions with biosensors.

The introduction in 1990 of a new biosensor technology based on surface plasmon resonance has revolutionized the measurement of antigen-antibody binding interactions. In this technique, one of the interacting partners is immobilized on a sensor chip and the binding of the other is followed by the increase in refractive index caused by the mass of bound species. The following immunochemical applications of this new technology will be described: (1) functional mapping of epitopes and paratopes by mutagenesis; (2) analysis of the thermodynamic parameters of the interaction; (3) measurement of the concentration of biologically active molecules; (4) selection of diagnostic probes.

Animals↗
PubMed1998

D-peptides as immunogens and diagnostic reagents.

There has been a regain of interest in the immunological applications of peptides assembled partly or totally from D-amino acids. Such peptides are much more stable to proteolysis than natural L-peptides and they have considerable potential as synthetic vaccines and as immunomodulators in T-cell responses. Retro-inverso, also called retro-all-D or retroenantio, peptide analogues that closely mimic the structure of protein antigens are obtained by assembling amino acid residues in the reverse order from that in the parent peptides and replacing L- by D-amino acids. Retro-all-D peptides corresponding to an immunodominant epitope of foot-and-mouth disease virus have been shown to elicit high levels of neutralizing antibodies in experimental animals. Certain retro-all-D peptide analogues of T-cell epitopes are able to bind to MHC class II molecules and may either lead to T-cell activation or inhibit deleterious T-cell responses.

Amino Acids↗
PubMed1998

Biosensor characterization of antigenic site A of foot-and-mouth disease virus presented in different vector systems.

The region 141-160 of the VP1 protein of foot-and-mouth disease virus known as site A is an immunodominant region that has been extensively studied for the purpose of developing a synthetic vaccine. In the present study, site A of foot-and-mouth disease virus was inserted in three different loops of the maltose-binding protein and its antigenicity was compared with site A presented as a conjugated synthetic peptide or inserted in beta-galactosidase. The affinity of antibodies elicited against the site A synthetic peptide was also compared with that of antibodies raised against the site A inserted within the two carrier proteins. Using biosensor technology it was possible to estimate the concentration of site A antibodies present in the various antisera and to show that site A fused to maltose-binding protein was a slightly better mimic of the epitope present in the virus particle than the synthetic peptide or the beta-galactosidase recombinant construct.

Animals↗
PubMed1998

Thermodynamic parameters in immunoassay.

Although affinity and kinetic measurements on their own provide useful information regarding the suitability of antibodies for various immunoassays, a thermodynamic analysis provices additional information that throws light on the molecular forces at work in the antigen-antibody interaction. It may then be possible to adjust assay conditions in order to favour either the association or dissociation of antigen-antibody complexes. A tenfold increase in binding affinity (K) corresponds to a free energy change of only 1.4 kcal/mol (5.8 kJ/mol) at 25 degrees C. This means that K values of 10(5) M-1 and 10(10) M-1 correspond to a free energy change (delta G) of 7.0 and 14.0 kcal/mol respectively. The entire range of affinity constants normally encountered in antigen-antibody interactions, therefore differs by no more than about 7 kcal/mol of free energy change, which is equivalent to only a few hydrogen bonds. In comparison, a single electrostatic interaction corresponds to about 4 kcal/mol of free energy change. A full description of the binding interaction requires an understanding of the change in hydration states of the reactants when the complex forms, and an assessment of the entropic andenthalpic effects of these changes. Contrary to earlier assumptions, it is now clear that antigen-antibody interactions are often accompanied by a large favourable enthalpy which more than compensates the unfavourable entropy.

Antibody Affinity↗