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 40 µg/mL of rabbit immune serum. Purified xylitol-specific antibodies appeared to be homogeneous by native PAGE with a pI of 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 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.