SIZE EFFECT ON THE ANTIBODY-PRODUCTION INDUCED BY BIODEGRADABLE MICROSPHERES CONTAINING ANTIGEN

Poly(L-lactic acid) (PLLA) microspheres containing a model antigen, ov albumin (OVA), were prepared by the evaporation method using double em ulsion, and fractionated into different sizes by counterflow elutriati on. Following the intraperitoneal (i.p.) and subcutaneous (s.c.) injec tion of the microspheres to mice, the titer of anti-OVA antibody in th e serum was measured to assess the size effect on the profile of antib ody production. OVA was released from the microspheres for 80 days, ir respective of the microsphere size. In both the s.c. and i.p. immuniza tion, the serum level of anti-OVA IgG antibody in the mice induced by the microspheres containing OVA was higher than that of free OVA when compared at the same dose. The serum level of antibody in the mice i.p . injected with the microspheres tended to increase with the decreasin g size. On the other hand in the s.c. immunization, the microsphere si ze had little influence on the antibody production. It is possible tha t the injected microspheres tend to aggregate in the s.c. tissue, disa ppearing the size effect on the antibody production. Since the amount of microspheres injected increases with the decreasing size when their OVA loading is fixed, the increase in the amount will promote the int eraction with immune cells, resulting in an enhanced antibody producti on. The cell interaction with the microspheres in the peritoneal cavit y seems to be influenced by their size to a greater extent than in the s.c. tissue, probably because of their more frequent interaction with immune cells. Copyright (C) 1996 Elsevier Science Ltd.