Background: The IgE-binding peptides Mag 1 and Mag 3 and the high-molecular-weight protein M-177 have been identified as parts of the apolipophorin-like group 14 house dust mite allergen. By analogy with the homologous insect proteins, apolipophorins are hydrophobic proteins found in lipid bodies and lipid transport particles. This explains why they degrade and are poorly represented in extracts. Methods: We have examined the T cell stimulation induced by a 341-residue recombinant Der p 14 peptide equivalent to the Mag 1 polypeptide examined by others. Results: Peripheral blood mononuclear cells from both allergic and non-allergic donors responded strongly in in vitro proliferation assays to the Der p 14 peptide to induce markedly more H-3-thymidine incorporation than Der p 2 and the release of Th2 cytokines. Conclusions: The apolipophorin-like group 14 allergens, despite their predicted hydrophobicity and lipid-binding activity, can induce high IgE responses and T cell stimulation. They appear to be important mite allergens unsuited to representation by aqueous extracts of mites. Copyright (C) 2001 S. Karger AG,Basel.