Carbondioxide feed and macronutrient supply were investigated regarding their effects on cell growth, cell size and cell-specific productivity. Our research reveals a stress related increase in mAb production for carbondioxide limitation, glucose overfeeding and increased glutamate supply as well as the importance of glutamine for proliferation. Together with the discovery of a non-linear correlation between cell enlargement an increased specific productivity, this marks the first step towards better process understanding and optimization.