IL6 and plasma cell myeloma: Additionally, we also tested the effect of IL-5 on HMCL proliferation in the presence of IL-6, a known growth cytokine for myeloma cells, to rule out any possible synergism between these 2 molecules as this has previously been observed for some MM cell lines.[21] However, the data shown in Figure S1 demonstrate that the proliferation of IL-6-stimulated MM cells is not affected by IL-5.