Modulation of hybridoma formation by dexamethasone.

: In an effort to determine the effect of dexamethasone on hybridoma formation, spleen cells from BALB/c mice hyperimmunized with sheep red blood cells (SRBC) were fused with mouse plasmacytoma cells (P3U1) in the presence of polyethylene glycol (PEG). Dexamethasone was added in decreasing doses (10(-3) to 10(-9) mM) to the hypoxanthine-aminopterin-thymide (HAT) medium immediately after the PEG-mediated cell fusion. 10(-3) mM of this steroid was found to inhibit markedly the number and size of hybridoma clones generated, while 10(-5) mM dexamethasone was shown to enhance hybridoma formation. The effect of 10(-3) mM dexamethasone was most pronounced when added immediately after fusion. When this dose was given 48 or 120 h after cell fusion, the extent of the inhibitory effect was less pronounced. High concentration of dexamethasone may also inhibit monoclonal antibody production by hybridomas once generated. An increase in the number of clones formed was observed when 10(-5) mM dexamethasone was added to HAT medium as well as an increase in the average colony size. Large clones were also observed with lower dexamethasone doses ranging from 10(-7) to 10(-9) mM. Possible mechanisms on the effect of dexamethasone on hybridoma formation are discussed.