A proinflammatory cytokine interleukin‐32β promotes the production of an anti‐inflammatory cytokine interleukin‐10

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Abstract
A new proinflammatory cytokine interleukin-32 (IL-32) has six isoforms. Although IL-32 can be detected in sera from patients suffering from Crohn’s disease and rheumatoid arthritis, it is unclear which isoforms are involved. To this end, we investigated the functions of the most abundant IL-32β by generating K562-IL-32β stable cell lines. This report confirms, using IL-32 small interfering RNA, that IL-32β induces an anti-inflammatory cytokine IL-10 in K562-IL-32β cells and U937 promonocytic cells, which express endogenous IL-32β upon phorbol 12-myristate 13-acetate (PMA) treatment, and monocyte-derived dendritic cells (DC) upon lipopolysaccharide (LPS) treatment. Interleukin-32β was induced in monocyte-derived macrophages by LPS and in monocyte-derived DC by LPS, poly(I:C), or anti-CD40 antibody, but was not induced by PMA. We showed that IL-32β expression was increased in a time-dependent manner in monocyte-derived DC upon LPS treatment and peaked at 24 hr. Production of IL-10 was exactly coincident with IL-32β expression, but IL-1β and tumour necrosis factor-α production peaked at 6 hr after LPS treatment, then steeply declined. Interleukin-12 p40 was induced at 9 hr and gradually increased until 48 hr, at which time IL-32β and IL-10 were no longer increased. Knock-down of IL-32β by IL-32 small interfering RNA led to the decrease of IL-10, but the increase of IL-12 in monocyte-derived DC, which means that IL-32β promotes IL-10 production, but limits IL-12 production. We also showed that IL-10 neutralization increases IL-12, IL-1β and tumour necrosis factor-α production, which implies that IL-10 suppresses such proinflammatory cytokines. Taken together, our results suggest that IL-32β upregulates the production of an anti-inflammatory cytokine IL-10, and then IL-10 suppresses proinflammatory cytokines.

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