Immunogenicity of antigens in boiled alginate microspheres

Vaccine efficacy can be enhanced by delivery of antigens in synthetic micro spheres. The process of antigen incorporation into microspheres can expose fragile antigens to damaging conditions, such as high temperatures, and to bacterial contamination. Maintenance of immunogenicity of several antigens and reduction of bacterial load in alginate microspheres following boiling was evaluated. Mice were immunized subcutaneously, initially and again 21 d ays later, with either non-boiled or boiled microspheres containing ovalbum in (OVA), a culture supernatant vaccine of Pasteurella haemolytica (PHV), o r a potassium thiocyanate extract of P. multocida (PTE). Serum samples were obtained prior to immunization and at the time of euthanasia 28 days later Culture of microspheres showed that boiling completely eliminated aerobic bacterial growth for OVA-containing microspheres, and reduced growth by a f actor of 10(4) for PTE microspheres. More bacteria were cultured after boil ing than before for PHV microspheres. ELISA performed on serum and intestin al lamina propria explant supernatants showed that immunogenicity of PHV mi crospheres was not altered by boiling. Polled OVA microspheres were still a ble to stimulate a significant serum IgG anti-OVA titer in mice, but boiled PTE microspheres completely lacked immunogenicity. Elispot assays of splee ns showed that only PHV microspheres were able to retain immunogenicity aft er boiling. Results indicate that boiling is not an effective means for red ucing the bacterial load of alginate microspheres and that the process is a ssociated with a diminution of vaccine immunogenicity.