Ige adjuvant activity of particles - What physical characteristics are important?

Diesel exhaust particles (DEP) are reported to increase the allergic immune response to ovalbumin (OVA) and pollen. There are studies reporting that b oth the adsorbed chemical substances and the carbon core of DEP may contrib ute to the immunoglobulin E (IgE) adjuvant effect. The aim of this study wa s to investigate which physical properties of particles per se, that is, th e particles by themselves, might be important for their IgE adjuvant effect , namely, dose weight, size, number, and surface area. Since DEP have a ten dency to form aggregates of varying shapes and sizes, evaluation of the rel ative importance of these characteristics is difficult using DEP. We theref ore decided to use well-characterized, spherical polystyrene particles (PSP ). We performed four different types of experiments, in which the total dos e weight (12.25 mg), size (0.1 mu m in diameter), total number 18 x 10(10)) , or total surface area (1300 cm(2)) of PSP, respectively, was kept constan t. NIH/Ola mice were given 2 intraperitoneal injections with PSP plus OVA o r OVA alone, over a 16-day period. The mice were exsanguinated at the end o f each experiment, and the serum concentration of IgE anti-OVA nas measured . The serum levels of IgE anti-OVA increased with both an increasing number and surface area of PSP. We found no clear association between PSP size an d the levels of IgE anti-OVA, but because of the relatively small size rang e of PSP used, no definitive conclusions can be made on whether size is an important factor for the IgE adjuvant effect of PSP. There seemed to be no covariation between the dose weight and the levels of IgE anti-OVA. Our fin dings indicate that the total number and total surface area of PSP, rather than the dose weight, are important parameters for the IgE adjuvant activit y front PSF: and possibly also for particles in general.