Young pigs have immature immune systems, this causes vaccines to have limited effects on neonatal piglets. Also after pigs ingest colostrum there immune system suppresses maternal antibodies. This creates a need for vaccines that can induce active immune responses in piglets before maternal antibodies decline to non-protective levels. Tests done on lab mice have shown that the complement component C3d has potent immune stimulating properties.  In addition, biochemical studies in lymphocytes suggest that C3d should block the suppressive effects of maternal antibodies, stimulating active immune responses. Researchers were able to clone the gene fragment coding for “porcine complement C3d” and have introduced modifications into the DNA sequence to allow expression of C3d in E. coli, for subsequent use in vaccines.