Factors affecting antibody accumulation and stability were investigated in transgenic plant cell cultures. Whereas IgG(1) antibody was stably maintained in media used for animal cell culture, there was a rapid loss over a period of 1-2 h of antibody added to sterile plant culture media. Antibody stability in Gamborg's B5 medium was improved in the absence of Mn. Tobacco suspensions producing IgG(1) antibody were used to test various medium-based strategies for improving antibody accumulation in plant culture. Even though growth was suppressed, antibody levels in the biomass and medium were increased in media containing mannitol at osmolalities up to approximately 450 mOsm x (kg of water)(-1). Adding gibberellic acid and haemin to the cultures was also beneficial, but the effects were not as great as those obtained under hyperosmolar conditions. Moderate increases in antibody accumulation were found by culturing plant cells in B5 medium without Mn.
