Mechanisms of the increased antibody production in hybridoma cells in response to hyperosmotic stress

The increasing monoclonal antibody market increases the impetus to improve yields. Increasing specific production can not only increase overall yield, but can reduce the operating, recovery and purification costs as well. In this study, hyperosmotic stress was used as a direct method to study the mechanism of the increased antibody production in hybridoma cells in batch culture. The specific antibody production rate, total cellular RNA, immunoglobulin mRNA, immunoglobulin degradation rate and assembly rate were investigated. Within 24 hours after increasing the osmolarity of the culture medium by 110 mOsm, the specific antibody production rate increased more than 60%. Osmotic stress also increased the total cellular RNA and immunoglobulin mRNA levels when stressed cells entered the stationary phase, but the increase in the immunoglobulin mRNA did not correlate with the increase in antibody production. The biosynthesis rate of immunoglobulins increased about 60% in the stressed cultures measured in a pulse-chase experiment. Osmotic stress did not increase antibody stability. Antibody assembly rate was calculated using a structured kinetic model. The assembly rate in the stressed culture was more than 60% higher than that in the control culture. Hence, the increased antibody production rate in response to osmotic stress is regulated at the translation and post-translational level. In signal transduction pathways, osmotic stress activated three protein kinases (MAPK, SAPK and p38) to different degrees. The activation of SAPK was more than 5-fold while the activation of SAPK and p38 was mild. The relationship between SAPK activation and the increased antibody production needs further investigation.