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 both the adsorbed chemical substances and the carbon core of DEP may contribute to the immunoglobulin E (IgE) adjuvant effect. The aim of this study was to investigate which physical properties of particles per se, that is, the particles by themselves, might be important for their IgE adjuvant effect, namely, dose weight, size, number, and surface area. Since DEP have a tendency to form aggregates of varying shapes and sizes, evaluation of the relative importance of these characteristics is difficult using DEP. We therefore decided to use well-characterized, spherical polystyrene particles (PSP). We performed four different types of experiments, in which the total dose weight (12.25 mg), size (0.1 μm in diameter), total number (8 x 10(10)), or total surface area (1300 cm(2)) of PSP, respectively, was kept constant. NIH/Ola mice were given 2 intraperitoneal injections with PSP plus OVA or OVA alone, over a 16-day period. The mice were exsanguinated at the end of each experiment, and the serum concentration of IgE anti-OVA was 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 and the levels of IgE anti-OVA, but because of the relatively small size range 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 findings indicate that the total number and total surface area of PSP, rather than the dose weight, are important parameters for the IgE adjuvant activity from PSP, and possibly also for particles in general.