Reductively aminated D-xylose-albumin conjugate as the immunogen for generation of IgG and IgE antibodies specific to D-xylitol, a haptenic allergen

Sugar alcohols are widely used as food additives and drug excipients. Xylitol, a five-carbon sugar alcohol, and a low-calorie alternative sweetener to sucrose (approx 40% fewer calories), has enjoyed an enviable record of safety, and allergic reactions to xylitol are very rare. A case of oral erosive eczema to xylitol has been reported recently Hanakawa, Y., Hanakawa, Y., Tohyama, M., Yamasaki, K., Hashimoto, K. (2005) Xylitol as a causative agent of oral erosive eczema. Brit. J. Dermatol. 152, 821-822]. Xylitol does not contain any reactive groups; hence, it is nonimmunogenic. In order to explain the immunogenicity of xylitol, polyclonal antibodies to xylitol have been raised using the reductive aminated product of D-xylose conjugated to bovine serum albumin (BSA) as the immunogen. Rabbits immunized with xylitol-BSA conjugate (52 haptens/molecule) gave a good antibody response. Purification of antixylitol antibodies was carried out using hapten-affinity chromatography on xylitol-keyhole limpet hemocyanin-Sepharose CL-6B; the yield was approximately 40 microg/mL of rabbit immune serum. Purified xylitol-specific antibodies appeared to be homogeneous by native PAGE with a pI of approximately 7.2 by isoelectric focusing. Although the purified antibodies are specific for the xylitoyl moiety of xylitol-protein conjugates, they reacted equally well with the Schiff base conjugate of xylosyl-protein conjugates (68% cross-reactivity) indicating that carbons 2 to 5 of xylitol act as an epitope. Xylitol antibodies showed excellent specificity towards xylitol and <4.4% cross-reactivity with D-xylose and various sugar alcohols except ribitol and galactitol, which showed approximately 11% and 8% cross-reactivity, respectively. D-Xylitol-BSA conjugate was used to raise IgE antibodies in BALB/c mice by repeated intradermal administration. Passive cutaneous anaphylaxis using the immune sera confirmed the haptenic nature of xylitol.