Cyclosporin A decreases human macrophage interleukin-6 synthesis at post-transcriptional level

IN addition to its well-established effect on T cells, cyclosporin A (CsA) also inhibits inflammatory cytokine production by macrophages. However, lit tle is known about the mechanism of action of CsA on macrophage cytokine pr oduction. We measured the effect of CsA on basal and phorbol-myristate-acet ate (PMA)-stimulated production of interleukin-6 using the human monocyte c ell Line U937 differentiated with dimethylsulfoxide (DMSO). Interleukin-6 l evels were measured in supernatant and cell lysates using specific enzyme-l inked immunosorbent assays. We found that CsA decreases not only IL-6 relea se but also cytokine synthesis. The concentration of CsA used did not affec t either cell viability or proliferation. Three possibilities may be advanc ed to explain the CsA-due decrease in IL-6 production by macrophages: (a) i nhibition of the synthesis of an early common regulatory protein, (b) inhib ition of cytokine gene transcription, or (c) modulation of post-transcripti onal events. The first possibility was tested by measuring the effect of cy cloheximide on the experimental system during the first 3 hours of culture. Although cycloheximide decreased total cytokine synthesis, the pattern of cytokine modulation by CsA persisted. These data suggest that CsA-mediated macrophage cytokine inhibition is not mediated by an early common regulator y protein. To further explore the inhibition mechanism, we measured IL-6 mR NA levels by Northern blot. IL-6 mRNA levels were unaffected by CsA both in resting and PMA-stimulated cells. We conclude that in human macrophages Cs A diminishes IL-6 production at post-transcriptional level.