Comparison of peptide-coating conditions in solid phase plate assays for detection of anti-peptide antibodies

Phage Display and Selections on Purified Antigens

The isolation of antibody fragments targeting proteins implicated in cancers and other diseases remains a crucial issue on targeted therapy or diagnostic tool development. In many case, the protein of interest, or a relevant portion of this protein such as its extracellular domain, is available as purified protein. In such cases, phage display on purified antigen is an easy and fast way to select antibody fragment able to efficiently bind this antigen. However the output of phage selection can vary significantly depending on the way to immobilize the purified antigen during selection. The following protocols describe the selection of phage antibody on purified antigen adsorbed on plastic, i.e., panning, or a selection in solution, using a biotinylated antigen as well as the corresponding screening produces, and give hints on the advantage and drawbacks of each approach.

Phage display and selections on purified antigens

The isolation of antibody fragments targeting proteins implicated in cancers and other diseases remains a crucial issue on targeted therapy or diagnostic tool development (Hoogenboom HR, Henderikx P, de Haard H. Adv Drug Deliv Rev 31 (1-2):5-31, 1998). In many case, the protein of interest, or a relevant portion of this protein such as its extracellular domain is available as purified protein. In such cases, phage display on purified antigen is an easy and fast way to select antibody fragment able to efficiently bind this antigen. However, the output of phage selection can vary significantly depending on the way to immobilize the purified antigen during selection. The following protocols describe the selection of phage antibody on purified antigen adsorbed on plastic, i.e. panning, or a selection in solution, using a biotinylated antigen as well as the corresponding screening produces, and gives hints on the advantage and drawbacks of each approach.

Use of alum and inactive Bordetella pertussis for generation of antibodies against synthetic peptides in mice

We have investigated the efficacy of the combined use of Alum and inactive Bordetella pertussis (iBP) adjuvants for eliciting anti-peptide antibodies. ICR mice were immunized four times at 3-week intervals with each of 7 free (i.e., not conjugated to any carrier) synthetic peptides of 15-17 amino acid residues in Alum + iBP, in the commonly used adjuvant protocols (CFA; CFA (initial) followed by IFA), or in CFA + iBP. Serum samples after 3 and 4 injections were tested by RIA. Use of Alum + iBP greatly increased the production of antibodies for most of the peptides. The results have important implications for human vaccine formulation involving peptides.

Direct coating of poly(lys) or acetyl-thio-acetyl peptides to polystyrene: the effects in an enzyme-linked immunosorbent assay

Direct adsorption of small peptides to polystyrene surfaces is often not satisfactory. Therefore, a simple and general coating procedure to improve the coating efficiency of small synthetic peptide antigens to polystyrene is described. In this study, the binding capacities of four small synthetic peptides N-terminally linked to various moieties during synthesis were compared to their parent counterparts in terms of the amount of peptide coat concentration required to achieve 50% of the maximum enzyme-linked immunosorbent assay signal. Elongation of a short epitope sequence by an N-terminal acetyl-thio-acetyl (Ata) group or a lysyl moiety resulted in an enormous reduction in peptide coat concentration for all tested peptides of net two to four orders of magnitude when corrected for chain elongation. The optimal length of the lysyl moiety depended on the length of the model peptide. Replacement of both extensions by analogues (i.e., Ata analogues and other basic amino acid residues in the case of the lysyl moiety) was possible without reducing their enhancing properties to a great extent. Additional experiments showed that a lysyl moiety consisting of a linear stretch of seven lysyl moiety consisting of a linear stretch of seven lysyl residues was more effective in comparison to a branched lysyl construct and could easily compete with the multiple antigen peptide approach.

Linear epitopes of the replication-activator protein of Epstein-Barr virus recognised by specific serum IgG in nasopharyngeal carcinoma

The linear antigenic epitopes of the Epstein-Barr virus replication activator protein (ZEBRA), recognised by specific serum IgG in nasopharyngeal carcinoma (NPC), were determined. This was achieved by synthesizing the entire amino acid sequence of ZEBRA as a set of 29, 22-residue peptides with an overlap of 14 amino acids. The ZEBRA peptides were tested in enzyme-linked immunosorbent assay (ELISA) for IgG binding in sera from 37 selected NPC patients who had IgG antibodies to the native ZEBRA protein. The most immunogenic epitope was peptide 1 at the amino-terminal end with 36 of the sera reactive against it. Further analysis of peptide 1, using the multipin peptide-scanning technique, defined a 10-amino-acid sequence FTPDPYQVPF, which was strongly bound by IgG. Two other regions of ZEBRA were also identified as immunodominant IgG epitopes, namely peptide 11 (amino acids 82-103) and peptide 19/20 (amino acids 146-175) with 8-13 of the NPC sera reactive against the peptides. The number of peptides reactive with individual NPC serum varies from 1 to 6 or more and there is some correlation between a greater number of peptide (at least 4) bound and a higher (at least 1:40) titre of serum IgA to viral capsid antigen. The immunodominant ZEBRA peptide 1 could be utilised in IgG ELISA for the detection of NPC.

Mapping the extracellular topography of the alpha-chain in free and in membrane-bound acetylcholine receptor by antibodies against overlapping peptides spanning the entire extracellular parts of the chain

The extracellular surface of the alpha-chain of Torpedo california acetylcholine receptor (AChR) was mapped for regions that are accessible to binding with antibodies against a panel of synthetic overlapping peptides which encompassed the entire extracellular parts of the chain. The binding of the antipeptide antibodies to membrane-bound AChR (mbAChR) and to isolated, soluble AChR was determined. The specificity of each antiserum was narrowed down by determining the extent of its cross-reaction with the two adjacent peptides that overlap the immunizing peptide. With mbAChR, high antibody reactivity was obtained with antisera against peptides alpha 1-16, alpha 89-104, alpha 158-174, alpha 262-276, and alpha 388-408. Lower, but significant, levels of reactivity were obtained with antibodies against peptides alpha 67-82, alpha 78-93, alpha 100-115, and alpha 111-126. On the other hand, free AChR bound high levels of antibodies against peptides alpha 34-49, alpha 78-93, alpha 134-150, alpha 170-186, and alpha 194-210. It also bound moderate levels of antibodies against peptides alpha 262-276 and alpha 388-408. Low, yet significant, levels of binding were exhibited by antibodies against peptides alpha 45-60, alpha 111-126, and alpha 122-138. These binding studies, which enabled a comparison of the accessible regions in mbAChR and free AChR, revealed that the receptor undergoes considerable changes in conformation upon removal from the cell membrane. The exposed regions found here are discussed in relation to the functional sites of AChR (i.e., the acetylcholine binding site, the regions that are recognized by anti-AChR antibodies, T-cells and autoimmune responses and the regions that bind short and long neurotoxins).

Mapping of the polypeptide chain organization of the main extracellular domain of the alpha-subunit in membrane-bound acetylcholine receptor by antipeptide antibodies spanning the entire domain

To study the organization of the polypeptide chain of the main extracellular domain of the nicotinic acetylcholine receptor (AChR) alpha-subunit, we examined the ability of the native membrane-bound AChR of Torpedo californica (T-AChR) to bind a panel of antibodies against overlapping synthetic peptides which collectively encompassed this entire domain. Antibodies against the alpha-chain peptides alpha 1-16, alpha 89-104 and alpha 158-174 were able to bind to membrane-bound T-AChR. Other anti-peptide antibodies showed little or no binding to T-AChR in the membrane. It is concluded that regions alpha 1-16, alpha 89-104 and alpha 158-174 are highly exposed on the surface of the alpha subunit of membrane-bound AChR.

Amino acid substitutions outside a preselected antigenic region in hemoglobin affect the binding to monoclonal antibodies obtained by immunization with the synthetic region

It is often assumed that amino acid substitutions outside a protein antigenic site have no effect on the reactivity of a protein variant with antibodies, especially monoclonal antibodies (mAbs). Substitutions that exert an effect on the reactivity of a protein variant with mAbs are frequently considered to be within the antigenic site of the mAb. To test this assumption, two mAbs [IgG1(k) and IgG2a(k)] were prepared by immunization with a synthetic peptide corresponding to region 63-78 of the alpha chain of human hemoglobin (Hb). The peptide was used as an immunogen in its free form (i.e., without conjugation to a carrier), so that the results will not be made ambiguous by peptide modification nor by an immune response to sites spanning peptide and protein carrier. In addition to their reaction with human Hb, the mAbs were also studied with four primate Hbs which had no substitutions within region alpha 63-78 and only a limited number of substitutions which occurred outside of, and at considerable distances in three-dimensional (3D) structure from, this region. Inhibition studies revealed substantial differences in the binding affinities of some of the primate Hbs, relative to human Hb. Some of the substitutions caused major decreases in binding, although they were at considerable distances in the 3D structure from the indicated site residues. It is concluded that substitutions in a protein, even when distant from an antigenic site, can exert major influences on the protein's reactivity with anti-site mAbs.