There are few studies investigating the effect of particles per se, that is the physical particle core, on specific IgE production and allergic immune responses. Such studies require the use of synthetic model particles or natural particles free of adsorbed substances. One aim of the research in our laboratory lately has been to explore the effect of the particle core on the specific IgE antibody production (adjuvant effect) by using well-characterized model particles such as polystyrene (PSP), amorphous silica, tetrafluoroethylen (teflon), and titanium dioxide (TiO2)(Granum et al., 2001a, b). After two intraperitoneal (ip) injections with the model allergen chicken ovalbumin (OVA) plus particles into naıve NIH/Ola mice (ie, mice not presensitized with OVA), we observed no qualitative differences in the adjuvant capacity of the different particles. All particle types resulted in mixed Th1/Th2-like responses (increased serum levels of OVA-specific Th2 dependent IgE antibodies and Th1 dependent IgG2a antibodies compared to mice given OVA alone; Granum et al., 2001a). Similar effects were found after intranasal or intratracheal instillation with OVA plus PSP or silica particles to naıve NIH/Ola mice (Granum et al., 2001a, b). In a study by Kurup et al.(1994), BALB/c mice were exposed intranasally with soluble Aspergillus antigen or Aspergillus antigen coupled to PSP. Mice exposed to the particulate antigens showed a stronger allergy-related Th2-like response than mice exposed to the soluble antigen, as evidenced by higher IgE levels in sera, more eosinophils in the blood, and higher levels of cytokine production from lung and spleen cells. By using synthetic particles, the studies cited above indicate that particles per se can exert an adjuvant effect on antibody responses independent of adsorbed chemical substances found on environmental particles. There are, in addition, several studies that have investigated the effect of particles on responses other than the adjuvant effect on antibody responses, such as inflammatory responses