Identification of peptide motifs recognized by a human IgG autoanti-IgE antibody using a phage display library

Applications of the phage display technology in molecular biology, biotechnology and medicine

The phage display technology is based on the presentation of peptide sequences on the surface of virions of bacteriophages. Its development led to creation of sophisticated systems based on the possibility of the presentation of a huge variability of peptides, attached to one of proteins of bacteriophage capsids. The use of such systems allowed for achieving enormous advantages in the processes of selection of bioactive molecules. In fact, the phage display technology has been employed in numerous fields of biotechnology, as diverse as immunological and biomedical applications (in both diagnostics and therapy), the formation of novel materials, and many others. In this paper, contrary to many other review articles which were focussed on either specific display systems or the use of phage display in selected fields, we present a comprehensive overview of various possibilities of applications of this technology. We discuss an usefulness of the phage display technology in various fields of science, medicine and the broad sense of biotechnology. This overview indicates the spread and importance of applications of microbial systems (exemplified by the phage display technology), pointing to the possibility of developing such sophisticated tools when advanced molecular methods are used in microbiological studies, accompanied with understanding of details of structures and functions of microbial entities (bacteriophages in this case).

Phage display: selecting straws instead of a needle from a haystack

An increasing number of peptides with specific binding affinity to various protein and even non-protein targets are being discovered from phage display libraries. The power of this method lies in its ability to efficiently and rapidly identify ligands with a desired target property from a large population of phage clones displaying diverse surface peptides. However, the search for the needle in the haystack does not always end successfully. False positive results may appear. Thus instead of specific binders phage with no actual affinity toward the target are recovered due to their propagation advantages or binding to other components of the screening system, such as the solid phase, capturing reagents, contaminants in the target sample or blocking agents, rather than the target. Biopanning experiments on different targets performed in our laboratory revealed some previously identified and many new target-unrelated peptide sequences, which have already been frequently described and published, but not yet recognized as target-unrelated. Distinguishing true binders from false positives is an important step toward phage display selections of greater integrity. This article thoroughly reviews and discusses already identified and new target-unrelated peptides and suggests strategies to avoid their isolation.

The role of innate immunity in asthma: leads and lessons from mouse models

According to the Hygiene Hypothesis, respiratory infections should protect individuals from allergic diseases including asthma, but epidemiologic data on the role of infections or exposure to microbial compounds in asthma are contradictory. Meanwhile, a number of murine models of airway sensitization are available facilitating the elucidation of pathways involved in asthma pathogenesis. Such studies have linked antigen presentation by activated pulmonary dendritic cells (DCs) with airway sensitization. Toll-like receptors (TLRs), which play a major role in innate immunity by sensing various microbial compounds, are expressed on DCs, as well as on mast cells (MCs). Activation of TLRs by administration of specific bacterial ligands, in particular lipopolysaccharide, can augment airway sensitization in mice, and there is evidence that this process involves TLR-dependent activation of DCs. Intriguingly, viral infection has been shown to increase airway inflammation in a murine asthma model via activation of DCs as well. TLR-4-dependent stimulation of MCs may also play a role in allergic sensitization in mice, and in vitro studies in murine cells show that ligation of TLRs expressed on MCs enhances degranulation. Therefore, evidence obtained from studies on mice indicates that innate immune responses may promote, rather than protect from, the development as well as the exacerbation of asthma.

Current progress in the understanding of IgE-FcepsilonRI interaction

The last decade has seen a wealth of studies aimed at the characterization of the binding between IgE and its high-affinity receptor, FcepsilonRI. IgE-FcepsilonRI complex formation is a major molecular event in atopic allergy. IgE-FcepsilonRI binding connects allergen recognition to cellular triggering, ultimately leading to disease manifestations. Consequently, pharmacological intervention at this site is of universal relevance for atopic allergy. Until recent years, the complexity of IgE-FcepsilonRI binding, together with the difficulty in obtaining fully functional recombinant IgE and FcepsilonRI derivatives, often led to confusion and difficulty in data interpretation. Major advances in the understanding of this intricate protein-protein interaction have now been accomplished. Most of the current knowledge on the IgE-FcepsilonRI recognition mode derives from long-lasting efforts in the field of structural biology. Protein engineering, high-throughput screening, immunological and biochemical studies also made relevant contributions in this domain. The data accumulated to date predict that IgE and FcepsilonRI use their modular architecture to approach each other in an asymmetric stepwise manner determining a 1:1 stoichiometry. This recognition appears to be enhanced by conformational changes occurring upon binding, leading to the well-known high-affinity. In conclusion, the vast amount of high-quality data available broadened our knowledge on the IgE-FcepsilonRI system; however, the fine structural details of the recognition process are still largely hypothetical. More studies are necessary to provide the experimental comprehensive picture required to carefully design efficient drugs acting at the IgE-FcepsilonRI interface.

Oral tolerance induction to Dermatophagoides pteronyssinus and Blomia tropicalis in sensitized mice: occurrence of natural autoantibodies to immunoglobulin E

BACKGROUND

The dust mites Dermatophagoides pteronyssinus (Dp) and Blomia tropicalis (Bt) are important sources of indoor allergens in tropical and subtropical countries. Murine models allow the analysis of the immune response and regulation of IgE production to Dp and Bt allergens. Oral tolerance induces unresponsiveness in naive animals, but its application in sensitized animals can provide useful information to improve allergy therapy.

OBJECTIVE

To study the profile of IgE and IgG subclasses antibody upon oral administration with Bt and Dp extract in previously sensitized mice. Further, the occurrence of autoantibodies IgG anti-IgE in the immunization and in the oral tolerance was investigated.

METHODS

A/Sn mice were immunized with Bt or Dp extract in alum, orally administrated with 0.25 mg of Bt or Dp extract or PBS at the 6th, 7th and 8th days after immunization and boosted twice with their respective allergens. To analyse the mice groups, specific IgE antibodies were measured by passive anaphylaxis reaction and specific IgG subclasses and anti-IgE IgG autoantibody by ELISA assay.

RESULTS

IgE levels were markedly increased in Bt-immunized mice compared with Dp-immunized mice. A distinct profile of the specific isotypes was verified in Bt-immunized mice with a preferential production of IgG3 and IgA antibodies, whereas Dp-immunized mice developed high titres of anti-Dp IgG1, IgG2a and IgG2b antibodies. The antigen feeding inhibited IgE response in both fed-mice groups but only Dp-fed mice presented decreased levels of IgG antibodies. Free anti-IgE IgG autoantibodies were detected mainly in the Dp-immunization and they correlated with the antibody isotypes found against the allergen.

CONCLUSIONS

This is the first time that the murine-type I hypersensitivity is employed to study Bt-immunization, showing a marked IgE production, associated with IgG response, which is at least in part driven by T-independent antigens. The oral tolerance protocol in previously sensitized animals was able to down-modulate IgE response and points out this route as a strategy for allergy therapy.

Selection of phage-display library peptides recognizing ethanol targets on proteins

There is a forthcoming link between chronic alcohol consumption and proteins covalently modified by ethanol metabolites and their antibodies. To identify sensitive probes of protein-ethanol conjugates, we screened for the ethanol-altered protein domains with a phage-display combinatorial peptide library. In principle, recognition of the epitopes by the library peptides occurs through protein-protein interactions. A general screening, M13-based library with 10(9) random sequences of linear heptameric peptides was used. The peptides were displayed in five copies each, as fusion proteins with phage's minor coat protein III. They were located on one end of the surface of the phage particles. The targets were a model protein, streptavidin, and protein-ethanol conjugates (hydroxyethyl radical- or acetaldehyde-modified bovine serum albumin). They were either immobilized on a surface by direct coating or affinity captured on floating beads. An enriched library of phages with the tightest peptide binders for each target was selected and amplified in a multiple-cycle biopanning in vitro procedure. Binders were characterized by DNA sequencing of the corresponding phages and by counter-screening with positive and negative targets in either an enzyme-linked immunosorbent assay or plaque assay. We obtained the HPQ motif for streptavidin and two unique subsets of peptides that recognized each ethanol target with a selectivity of two orders of magnitude above the carrier protein and controls. The application of biopanning processes, coupled with phage-display peptide libraries on biological fluids and tissues, could provide a systematic mapping of protein--ethanol conjugates and supply a means for early diagnosis and prognosis of chronic alcohol consumption in human beings.