Immunization of mouse spleen cell cultures in the absence of serum and its proteins using SiO2 and 2-mercaptoethanol.

High recoveries of plaque-forming cells were obtained in a serum-free medium using 2-mercaptoethanol and SiO2. Under such conditions an increase in the number of plaque-forming cells occurred between the fourth and fifth day of incubation, as compared with cultures with foetal calf serum. The addition of glutathione to the medium had a stimulating effect, it was however not absolutely necessary for a positive response. The recovery of plaque-forming cells was strongly influenced by an interdependence of cell density and amount of SiO2 gel particles.