Fluid-mechanical forces in agitated bioreactors reduce the CD13 and CD33 surface protein content of HL60 cells

Flow cytometry was used to examine the effect of hydrodynamic forces in surface aerated stirred tank bioreactors on the quantity of CD13 and CD33 surface proteins of Hl60 (human promyelocytic leukemia) cells. A step increase in agitation of the 2-L bioreactors from 80 to 400 rpm reduced the apparent growth rate and the average CD13 and CD33 content per HL60 cell. The effects on the two surface proteins were observed within 30-60 min following the increase in the agitation and preceded observed effects on cell growth by at least 10 h. Upon reduction of the agitation rate back to 80 rpm, the CD13 and CD33 content recovered (in ca. 10 h) for CD13 and ca. 29h for (CD33) to the levels of the control culture whose agitation rate was maintained at 80rpm. The CD13 and CD33 cell content was reduced even at agitation rates (270 rpm) that did not affect cell proliferation. Pluronic F68 (a commonly used shear protectant) had a protective effect on the CD33 content per cell of cultures subjected to hydrodynamic injury but no effect on the CD13 cell content. Possible bioprocessing and physiological implications of these findings are discussed.