Interleukin (IL) 4 counteracts the helper effect of IL 2 on antigen‐activated human B cells

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Abstract
We tested the effect of interleukin (IL)4 on the specific IgM antibody response induced by trinitrophenylated‐polyacrylamide beads (TNP‐PAA) in cultures of human B cells. T cell help was provided by exogeneous IL2. IL4 profoundly suppressed the response to optimal concentrations (50 U/ml) of IL2, with a 50% inhibitory concentration of 6 U/ml. This was due neither to a shift in the kinetics nor to a switch to an IgG response. The production of anti‐TNP antibody (as measured by an enzyme‐linked immunosorbent assay in the culture supernatant) was inhibited to the same extent as the generation of plaque‐forming cells. The effect of IL4 was completely abolished by a neutralizing antibody toward IL4. Kinetic studies showed that IL4 had to be present during the first 48 h of culture to fully inhibit the response. The sequential stimulation of B cells by antigen and by IL2 showed that IL4 does not negatively interfere with signaling through membrane Ig but counteracts the effect of IL2 on antigen‐activated B cells.