Immunogenic and allergenic potentials of natural and recombinant innocuous proteins

A review on emerging frontiers of house dust mite and cockroach allergy research

Currently, mankind is afflicted with diversified health issues, allergies being a common, yet little understood malady. Allergies, the outcome of a baffled immune system encompasses myriad allergens and causes an array of health consequences, ranging from transient to recurrent and mild to fatal. Indoor allergy is a serious hypersensitivity in genetically-predisposed people, triggered by ingestion, inhalation or mere contact of allergens, of which mite and cockroaches are one of the most-represented constituents. Arduous to eliminate, these aeroallergens pose constant health challenges, mostly manifested as respiratory and dermatological inflammations, leading to further aggravations if unrestrained. Recent times have seen an unprecedented endeavour to understand the conformation of these allergens, their immune manipulative ploys and other underlying causes of pathogenesis, most importantly therapies. Yet a large section of vulnerable people is ignorant of these innocuous-looking immune irritants, prevailing around them, and continues to suffer. This review aims to expedite this field by a concise, informative account of seminal findings in the past few years, with particular emphasis on leading frontiers like genome-wide association studies (GWAS), epitope mapping, metabolomics etc. Drawbacks linked to current approaches and solutions to overcome them have been proposed.

Development of oral immunotherapy model using B10.A mice and egg white lysozyme

Oral immunotherapy for food allergy has been the focus of a lot of attention recently. The patients have to eat allergenic food instead of eliminating it in this therapy and there is no established standard method yet. To promote clear understanding and improvement of oral immunotherapy, the present study using B10.A mice investigated the effect of multiple oral administration of a model antigen, egg-white lysozyme, on both the antibody response and the anaphylactic reaction induced by subsequent administration of lysozyme. Various doses of egg-white lysozyme (0-100 mg/mouse) were administered to mice intragastrically for 6 d; then additional lysozyme was administered via the intraperitoneal route in all groups. Lysozyme-specific antibody responses were promptly induced by the first oral administration and enhanced by intraperitoneal administration. An anaphylactic reaction was further induced in these sensitized mice by intragastric administration of lysozyme, and the symptoms of shock were compared in order to evaluate the effects of pretreatment. Interestingly, the decrease in rectal temperature which is one of the common anaphylactic symptoms in mice was suppressed in all of the oral pre-administration groups, and the effects were highest in the group that received 20 mg. Consequently, this study using B10.A mice has shown that sensitization can be induced by intragastric administration of lysozyme instead of oral tolerance; however, anaphylactic shock induced by subsequent intragastric administration of lysozyme is suppressed. This mouse model would be useful for assessing the method of oral immunotherapy.

Sequence microheterogeneity of parvalbumin, the major fish allergen

The microheterogeneity of amino acid sequence observed in various allergens may affect immune response, but incidence of sequence microheterogeneity in allergens and its relation to their allergenicity are unclear. The occurrence of sequence microheterogeneity in major fish allergen, parvalbumin (PA), has been explored using bioinformatics approaches. 44% of 111 species with known PA sequence have PA isoforms. 41% of these species exhibit from 1 to 4 cases of PA sequence microheterogeneity, i.e. unique pairs of PA isoforms with sequence identity above 90%. 29% of 210 PA sequences studied are characterized by microheterogeneity. The occurrence of allergens among them is 2.5-fold higher than among other PAs. The incidence of sequence microheterogeneity within more allergenic β isoform of PA is 2.0-fold lower than that for its less allergenic α isoform. 39 residues affected by PA microheterogeneity are concentrated in the region of helices A, B, F, while helices D and E are the most conservative region. 44% and 11% of the microheterogeneous substitutions are located in the species-specific and cross-reactive IgE-binding epitopes of PAs, respectively. 45% and 48% of the substitution cases are predicted to cause notable changes in protein disorder propensity and protein stability, respectively. Hence, the increased allergenicity rate among PAs having microheterogeneous isoforms can be related to differences in their IgE-binding caused directly or in an allosteric manner. Overall, sequence microheterogeneity is shown to be inherent to many of PAs and likely contributes to PA allergenicity.

Mobilization of seed protein reserves

The mobilization of seed storage proteins upon seed imbibition and germination is a crucial process in the establishment of the seedling. Storage proteins fold compactly, presenting only a few vulnerable regions for initial proteolytic digestion. Evolutionarily related storage proteins have similar three-dimensional structure, and thus tend to be initially cleaved at similar sites. The initial cleavage makes possible subsequent rapid and extensive breakdown catalyzed by endo- and exopeptidases. The proteolytic enzymes that degrade the storage proteins during mobilization identified so far are mostly cysteine proteases, but also include serine, aspartic and metalloproteases. Plants often ensure early initiation of storage protein mobilization by depositing active proteases during seed maturation, in the very compartments where storage proteins are sequestered. Various means are used in such cases to prevent proteolytic attack until after imbibition of the seed with water. This constraint, however, is not always enforced as the dry seeds of some plant species contain proteolytic intermediates as a result of limited proteolysis of some storage proteins. Besides addressing fundamental questions in plant protein metabolism, studies of the mobilization of storage proteins will point out proteolytic events to avoid in large-scale production of cloned products in seeds. Conversely, proteolytic enzymes may be applied toward reduction of food allergens, many of which are seed storage proteins.

A draining lymph node assay (DLNA) for assessing the sensitizing potential of proteins

There is a need for a simple and predictive model to identify the respiratory sensitization potential of (novel) proteins. The present study examined the use of a mouse draining lymph node assay (DLNA) approach, employing several routes of exposure, as a possible starting point for assessing protein sensitization potential. Consistent with the experimental procedure for the standard local lymph node assay (LLNA), female BALB/c mice were dosed dermally (topical), intranasally (IN) or by oropharyngeal aspiration (OP) on days 1, 2 and 3, and proliferation in the relevant draining lymph nodes was measured on day 6. For each route, the auricular, superficial cervical and tracheobronchial lymph nodes (TBLN) were evaluated following treatment with Subtilisin Carlsberg (SUB; a potent sensitizer/allergen), ovalbumin (OVA; a potent food allergen), beta-lactoglobulin (BLG; a moderate food allergen), and keyhole limpet hemocyanin (KLH; a strong immunogen with no reports of respiratory sensitization). Initial studies with OVA indicated that dermal administration did not stimulate lymph node proliferation. Responses in the tracheobronchial lymph node were most dramatic (stimulation indices up to 100) and reproducible for both the IN and OP routes. In a comparative experiment, all proteins induced lymph node proliferation with a rank order potency of SUB>KLH>OVA>BLG. The influence of the endotoxin content on lymph node proliferation was determined to be minimal, and did not impact the rank order potency. Molecular characterization of the TBLN at an equipotent proliferative dose was conducted for select gene transcripts based on research examining chemical sensitizers. Expression profiles differed among the four proteins, but the relevance of these responses was not clear and they did not further discriminate their allergic potential. These data illustrate both the opportunities and challenges associated with the examination of the draining lymph node proliferative response to assess the allergenic potential of proteins.

(Xeno)estrogen regulation of food allergy

Food allergy and other types of allergies are becoming epidemic in both the developed and developing countries. A large amount of information is available in literature that (xeno)estrogens can regulate the immune response in general, and the development of allergy in particular; however, the effect of (xeno)estrogens on food allergy is basically unknown. With increasing use of xenobiotics worldwide, chemicals with estrogenic activity have been accumulating in our environment. This review has summarized the current literature relating to the topic (xeno)estrogen regulation of food allergy. The effect of (xeno)estrogens on enterocytes, proteases for protein hydrolysis, dendritic cells and T-regulatory cells in the gastrointestinal tract has been discussed. Finally, considering the current confusion in literature regarding the effect of phytoestrogen genistein on the immune system, a brief discussion has been included for its effect on T(H)1-T(H)2 polarization, and possibly food allergy in its relation to windows of exposure. Sufficient evidences exist to support the notion that (xeno)estrogens can regulate food allergy, with the developmental periods more sensitive. Further clinical and animal studies are needed to determine the causal relationship between the exposure of (xeno)estrogens and incidence of food allergy, and the underlying mechanisms.

Safety assessment of food products from r-DNA animals

Recombinant-DNA (transgenic) animals intended for food production are approaching the market. Among them, recombinant-DNA fishes constitute the most advanced case. As a result, intergovernmental organizations are working on guidelines which would eventually become international standards for national food safety assessments of these products. This article reviews the emerging elements for the food safety assessment of products derived from recombinant-DNA animals. These elements will become highly relevant both for researchers and regulators interested in developing or analyzing recombinant-DNA animals intended to be used in the commercial elaboration of food products. It also provides references to science-based tools that can be used to support food safety assessments. Finally, it proposes recommendations for the further development of biosafety assessment methodologies in this area.

Animal models of anaphylaxis

PURPOSE OF REVIEW

In this review we will focus on recent advances in the role of mast cells in the pathophysiology of insect allergy and the possible mechanisms of mast cell activation in anaphylaxis.

RECENT FINDINGS

Anaphylactic reactions in the mouse can be induced by several independent pathways involving immunoglobulin E, immunoglobulin free light chains, or immunoglobulin G. There is considerable evidence that mast cells play a central role in anaphylactic reactions to insect stings. Mast cells can be directly activated by components of insect venom or after allergic sensitization. Of interest is the observation that mast cells are not only effector cells in insect allergy, but may also play a protective role in preventing the development of severe anaphylactic responses or by controlling inflammatory reactions by modulation of antigen-specific T-cell responses.

SUMMARY

The contribution of mast cells in anaphylactic responses to insect venom may be heterogeneous. On the one hand, activation of mast cells contributes to the pathology by the release of bioactive and tissue-damaging mediators. However, mast cell activation may neutralize constituents in insect venom and defend against the adverse effects of these toxins or they may modulate inflammation through downregulation of antigen-specific immune responses.