It’s estimated that around 10% of the US population has peanut allergies, a medical emergency that will be treated but not cured. In comparison with those without allergies, these individuals are at a greater risk of anaphylaxis. Hence, there’s a have to develop novel therapies to treat peanut and other food allergies. A recent Frontiers in Immunology journal study by University of North Carolina at Chapel Hill and Vanderbilt University researchers has created an in vitro system to find out potential therapeutics targeting sensitized effector cells based on human, allergen-specific, Immunoglobulin E (IgE) monoclonal antibodies (mAbs).

Study: Novel peanut-specific human IgE monoclonal antibodies enable screens for inhibitors of the effector phase in food allergy. Image Credit: Albina Gavrilovic / Shutterstock

How does Allergic Response Occur?

Allergic reactions are driven mainly by mast cells (MCs). Throughout the allergy effector phase, mast cells are activated because of crosslinking between allergenic antigens and allergen-specific immunoglobulin (Ig)E, which binds to the IgE receptor (FcϵRI) on MCs. The activated MCs promote allergic symptoms by degranulating and releasing previously formed mediators. 

Preformed mediators, comparable to vasoactive amines, the cytokine tumor necrosis factor (TNF)-alpha, and proteases, are stored in MC cytoplasmic granules. Interestingly, MCs also synthesize additional cytokines and de novo lipid mediators to take care of the allergic symptoms. Hence, latest food allergy treatments might be designed by targeting MC activity in the course of the allergy effector phase. 

Based on a murine allergic peritonitis model and passive cutaneous anaphylaxis models, MC inhibitory receptors, comparable to sialic acid-binding immunoglobulin-like lectin (Siglec)-8 and CD300a, mitigate allergic inflammation and MC degranulation.

Models to Discover Therapeutic Targets for Inhibiting Food Allergic Reactions

Antigen-specific, IgE-mediated MC activation was inhibited by nanoparticles co-displaying antigen and Siglec-8 ligands in vitro. Moreover, it could also suppress anaphylaxis in siglec-8 transgenic murine models. Although few studies have determined the effect of inhibition of MCs sensitized to the food allergen, i.e., chicken egg ovalbumin (OVA), researchers haven’t yet determined whether targeting CD300a or Siglec-8 affects in vitro MC activation in response to peanut.

Several in vitro models of the allergy effector phase have been developed based on purified human IgE antibodies. These models revealed that anti-human IgE antibodies at all times crosslinked IgE-FcεRI complexes on the MC and induced degranulation. Nonetheless, this was not the case with MCs sensitized to human sera containing anti-food allergen IgE. On this case, degranulation didn’t at all times occur within the presence of specific food allergens.

Around 30% of patients with food allergies are allergic to a couple of food. Hence, reproducibility issues occur in models that used human plasma to sensitize MCs because of variability in IgE levels and IgE specificity to multiple allergens. Subsequently, alternative in vitro models of food-allergen-induced MC degranulation are required to find out MC inhibitory receptors and assess the consequences of potential therapeutic agents that may goal these inhibitory receptors.

Development of Potential Therapeutics against Peanut Allergy

A novel in vitro system was designed to mimic the effector phase of peanut allergy, using naturally occurring peanut-specific human IgE monoclonal antibodies (mAbs) for sensitization of a longtime effector cell line.

Two novel human peanut-specific IgE mAbs were generated using human hybridoma techniques, which were used to sensitize rat basophilic leukemia (RBL) SX-38 cells expressing the human IgE receptor (FcϵRI). These peanut-specific human IgE mAbs might be crosslinked directly with clinically relevant food allergen peanut, which reproducibly elicits allergic effector cell activation and degranulation.

After stimulation with peanuts, cytokine production, beta-hexosaminidase release (degranulation marker), and phosphorylation of signal transduction proteins downstream of FcϵRI were measured. The extent of degranulation was also estimated after engaging inhibitory receptors CD300a and Siglec-8.

Previous studies have proposed immunoreceptor tyrosine-based inhibition motif (ITIM)-containing inhibitory mast cell surface receptors as possible pharmaceutical targets that may inhibit degranulation and MC activation upon food allergy. Here, scientists evaluated the effect of monoclonal antibodies specific for CD300a and Siglec-8 receptors on allergic effector cells sensitized with peanut-specific IgE. 

The findings related to Siglec-8 supported the proof of concept related to the commentary of in vitro system that detected inhibitors of MC degranulation. Notably, the CD300 receptor family was found to be a possible therapeutic goal for blocking peanut-specific allergic effector cell activation and degranulation.

The underlying mechanism of Siglec-8-mediated inhibition of MC has been related to direct interactions between Siglec-8 and signaling molecules downstream of FcϵRI.

In the longer term, scientists can use this in vitro model to determine whether phosphatases are linked with CD300a and Siglec-8 signaling within the RBL SX-38 effector cell line. The important advantage of the brand new model is that it enables direct detection of potential therapeutics on effector cell activation by eliminating variables introduced when human plasma is used for sensitization. Moreover, this technique removes non-relevant IgE, multiclonal allergen-specific IgE, and other irrelevant antibody subclasses, which is advantageous since it allows rapid screening for potential candidates for effector cell inhibition in food allergy.