Effects of amino acid substitutions outside an antigenic site on protein binding to monoclonal antibodies of predetermined specificity obtained by peptide immunization: demonstration with region 113-120 (antigenic site 4) of myoglobin

A hemagglutinin-derived peptide-vaccine ignored by virus-neutralizing passive antibodies, protects against murine measles encephalitis

The neutralizing and protective monoclonal antibody BH47 defines the sequential epitope H236-255 of the measles virus hemagglutinin protein (MV-H). The objective of this study was to design peptides combining this B cell epitope (BCE) with different T cell epitopes (TCE) to obtain protective immunity. Most TTB peptides based on the 15mer BCE H236-250 induced MV-crossreactive antibodies, but only certain TCE induced virus neutralizing antibodies. The shortest BCE required for MV-reactivity and -neutralization was the 8mer H243-250 containing residue R243 implicated in CD46 down-regulation. Sera obtained after immunization with the TTB peptide containing the MV-derived TCE F421-435 protected mice against a lethal challenge with a neuro-adapted MV strain. Our results further demonstrate that this TTB peptide is fully immunogenic, even in the presence of protective levels of pre-existing MV-specific antibodies, suggesting that subunit vaccines based on such peptides could potentially be used to immunize infants in the presence of persisting maternal antibodies. It is therefore interesting that neutralizing antibodies were also obtained with a TTB peptide comprising a human promiscuous TCE (tt830). However, our results also emphasize the need to test sera induced with epitope-based vaccines against different virus strains, in particular if the epitope is not fully conserved.

The molecular basis of virus crossreactivity and neutralisation after immunisation with optimised chimeric peptides mimicking a putative helical epitope of the measles virus hemagglutinin protein

The loop comprising aminoacids H236-256, connects two strands of sheet 1 of the propeller-like hemagglutinin (H) protein of the measles virus (MV) and contains a putative active site residue (R253), a residue implicated in CD46-downregulation (R243) and the minimal epitope E245L-QL249 of the neutralising and protective monoclonal antibody BH129. The objective of this study was to design synthetic peptides which induce neutralising antibodies against this important functional domain. Peptide-design was based on the colinear synthesis of this sequential B cell epitope (BCE) with different T cell epitopes (TCE). Chimeric constructs were systematically optimised with respect to length and copy number of the BCE and the nature and orientation of the TCE. Surprisingly, the induction of MV-crossreactive antibodies did not correlate with the antigenicity of the peptides. The best MV-crossreactive antibodies were obtained with TB oriented constructs containing TCEs of the MV fusion (F) protein and the BCE H236-250 (TB15mer) or H236-255 (TB20mer). In vitro virus-neutralising sera were obtained solely with the latter construct. A glycine scan showed that binding to MV depended on a defined pattern of contact residues compatible with the putative alpha helical nature of this epitope. The contact residues of the neutralising serum (S244EL-QL249) differed from those of the non-neutralising serum (S244EL246) but no unique differences in the immunoglobulin subclasses were detected. Surface plasmon resonance measurements detected a higher affinity for the neutralising serum compared to the TB15mer serum. These results emphasize the need of an optimal design of immunogenic peptides which cannot always be guided by the antigenicity of the peptide constructs. This study demonstrates that neutralising antibodies can be generated with peptides mimicking this helical epitope, provided that the critical contact residues are recognized with high affinity and underlines the potential of the epitope as an element of a future subunit vaccine.

Epitopic analysis and quantification of bovine myoglobin with monoclonal antibodies

Seven rat monoclonal antibodies (MAb) for bovine myoglobin were produced. Five antibodies reacted with surface-absorbed myoglobin whereas the two remainders reacted only in a sandwich type ELISA. The ability of different antibodies to bind simultaneously to myoglobin was examined by competition and additivity experiments and three noncompeting epitope regions were found. A two-site enzyme immunoassay was developed and allowed quantification of 30 ng/ml bovine myoglobin. These antibodies should be valuable tools in comparative studies for immunological reactivity of mammalian myoglobins and for myoglobin measurement in serum and urine of myopathic animals.