Abstact

BACKGROUND AND OBJECTIVES Nonspecific lipid transfer proteins (nsLTPs) are frequently cross-reactive allergens that hamper diagnosis and avoidance. It is challenging to distinguish cross-reactivity from cosensitization with polyclonal serum owing to the presence of a few promiscuous antibodies or many highly specific antibodies. Objective: We hypothesized that a robust analysis of more human monoclonal antibodies (mAbs) would enable us to compare crossreactivity with cosensitization. METHODS Human monoclonal antibodies were cloned from allergic patients via single cell sequencing and screened for affinity to extracts and recombinant allergens. Ara h 9 was expressed and crystallized with the mAb IGX-3103. Affinity for nsLTPs was explored using molecular modeling, site-directed mutagenesis, and ELISA. RESULTS A human IgG4 mAb named IGX-3103 was discovered from a type 2-polarized memory B cell expressing CD23, IL-4Ra, and germline IGHE. IGX-3103 bound to 19 different type 1 nsLTP allergens and to extracts from sources without a characterized nsLTP allergen. The structure showed that IGX-3103 induced a conformational change in Ara h 9, enabling a hydrophobic residue from the antibody, Phe104, to enter the lipid binding cavity. Key residues in the epitope were identified to include Leu1, Ser2, Cys3, Lys39, and Asp43 in Ara h 9; these residues are conserved across type 1 nsLTPs, thus explaining the promiscuity of IGX-3103. CONCLUSIONS IGX-3103 is an example of a human mAb with cross-reactivity to pollen, fruit, and seed type 1 nsLTPs. This observation anecdotally supports the possibility that a few promiscuous mAbs could be driving cross-reactivity.