Effect of ammonium ion and extracellular pH on hybridoma cell metabolism and antibody production

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Abstract
The effects of NH4Cl addition on batch hybridoma cell growth at different external pH values (pHe) were investigated in a bioreactor at constant pH and dissolved oxygen concentration. In agreement with measurements in flasks, changes in pHe over the range 6.8–7.6 had minor effects on growth. Addition of 3 mM NH4Cl had little effect on cell growth while 10 mM NH4Cl caused a substantial growth inhibition, Measurements of the effects of pHe and NH4Cl concentration on cell metabolism gave similar results for cells grown in flasks in an incubator and in the bioreactor. As pHe decreases, the integral cell yield on glucose increases. There is a correlation between the effects of pHe on glycolysis and previous measurements of its effects on intracellular pH (pHi). Increases in NH4Cl concentration were previously determined to decrease pHi and are shown here to decrease the integral cell yield on glucose. At all pHe values in the absence of NH4Cl, glutamine is depleted at the time the maximum cell density is reached. Both pHe decreases and NH4Cl concentration increases lead to decreases in the integral cell yield on glutamine. Changes in pHe and in the NH4Cl concentration that cause growth inhibition have no effect on the specific antibody production rate for cells grown in flasks in an incubator or in the bioreactor. Changes in the NH4Cl concentration have no effect on the quality of the antibody produced, to a first level of characterization.