In previous experiments with the 55-6 hybridoma cell line, we showed that cell stimulationwith
anti-mouse surface immunoglobulin G
antibody (
anti-mIgG) increased both CD40 expressionand specific monoclonal
antibody (mAb) production rate. Cell preincubation with lipopolysaccharide (LPS) prior to
anti-mIgG stimulation enhanced these results. Moreover, the expressionof both CD40 and surface immunoglobulin G (sIgG) were higher for cells in the G1 phase ofthe cell cycle. Therefore, to determine the relationship between cell cycle position, CD40expression, and mAb productivity, in this work cells were synchronized in the G1 phase bythymidine block. In addition, synchronized cells were subjected to different treatments with
anti-mIgG. Although synchronized cells showed a slight increase in both CD40 expression andmaximum specific growth rate (
max) compared with unsynchronized cells, specific productivitydid not show signific
ant changes. However, the stimulation of synchronized cells with
anti-mIgG increased over 65% the expression of CD40 and over 50% the specific productivity incomparison with that obtained on unsynchronized cells after
anti-mIgG stimulation. These dataimproved additionally over 15 and 60%, respectively, by adding 2 mM thymidine to the culturemedium. These results suggest that the effect of the positive association between G1 phase,CD40 expression, and specific productivity is subordinated to the effect of
anti-mIgG stimulation,which is enhanced by increasing the percentage of cells on the G1 phase of the cell cycle.Contrary to expectations, LPS preincubation of synchronized cells prior to
anti-mIgG stimulationdid not increase the specific productivity in comparison with non-preincubated cells, and theexpression of CD40 was minor compared to that on non-preincubated cells.