An absolute requirement for 2-mercaptoethanol in the in vitro primary immune response in the absence of serum

Using a serum-free medium, high recoveries of plaque-forming cells (PFCs) were obtained up to 5 days of incubation in the in vitro primary immune response. Under these conditions, the presence in the medium of 2-mercaptoethanol was an absolute requirement. In order to obtain maximal recoveries of PFCs, the antigen and 2-mercaptoethanol had to be present from the start of the culture, while the addition of fetuin could be delayed for 24 h without any loss of PFCs. The 2-mercaptoethanol could be replaced by (dialysed) human serum.