Allergy to peanut lipid transfer protein (LTP): frequency and cross-reactivity between peanut and peach LTP.

BACKGROUND Lipid transfer protein (LTP) is a widely cross-reacting plant pan-allergen, and sensitized patients may react to many foods. Although peanut allergy is frequently reported by LTP-allergic patients, the evidence of the presence of an allergen homologous to LTP in peanuts is limited. OBJECTIVE To assess the prevalence of peanut allergy in patients sensitized to LTP, detect any allergen homologous to LTP in peanuts, and assess its cross-reactivity with peach LTP. METHODS Spanish and Italian adults monosensitized to LTP were interviewed for possible peanut allergy and underwent skin prick tests (SPTs) with peanut extract. Sera from 32 peanut-allergic patients were assayed for peanut-specific IgE by direct ELISA and the Real Test; the serum showing the strongest reactivity was used in immunoblot analysis. RESULTS 74/114 (65%) patients were sensitized to peanuts, and 37 (32% of the whole population; 50% of those sensitized) were clinically allergic. Positive histories were validated by open oral food challenges in 13/13 cases. No SPT-negative patients reported clinical allergy to peanuts. Thus, in this selected population, sensitivity and negative predictive value of peanut SPTs were 100%, whereas specificity and positive predictive value were poor (52% and 32%, respectively). Only 2/32 sera scored positive in both in vitro assays and 4 reacted in the Real Test alone. In immunoblot, the serum studied reacted at about 10 kDa against the peanut extract; pre-adsorption with purified peach LTP totally inhibited such reactivity. CONCLUSIONS Peanut sensitization is frequent among LTP-allergic patients and is clinically significant in about 50% of cases. Peanut tolerance should be assessed in LTP-allergic patients positive on peanut SPTs. Peanut LTP seemingly shares all allergenic determinants with peach LTP.