Development of Serum-Free Culture Systems for an Immortalized Porcine Kidney-Derived Macrophage Cell Line.

The immortalized porcine kidney-derived macrophage (IPKM) cell line is an excellent resource that has proven to be an effective for the production of various strains of African swine fever virus (ASFV). In this study, we developed a serum-free medium to replace the standard serum-containing medium and established the long-term subculture of IPKM cells. We used KnockOut serum replacement instead of serum. As the expression of several cytokines and their receptors were observed in IPKM cells, we examined their effect and found that porcine colony stimulating factor 1 (pCSF1) and pCSF2 were essential for the proliferation of IPKM cells. Furthermore, the addition of 2% polyvinylpyrrolidone K90 to the medium improved cell adhesion and allowed for the stable long-term subculture of IPKM cells. The proportion of cells with a normal number of chromosomes (2n = 38) was similar to that of IPKM cells cultured in a serum-containing medium. Moreover, we investigated the spinner flask suspension culture without using microcarrier beads. Finally, we developed a modified serum- and calcium-free medium in which IPKM cells could be successfully cultured for an extended period. Whether grown in adherent or suspension culture, the expression of the macrophage-specific markers, CD172a, CD203a, and Iba1, remained positive, indicating that IPKM cells retained their macrophage properties.