Modulation of IL-1α, IL-1β, and 25K Mr Non-IL-1 Activity Released by Human Mononuclear Cells

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Abstract
To determine if the release of IL-1α and IL-1β by cultured PBMC could be independently modulated by different exogenous stimuli, we examined the effect of LPS, IFNγ, latex beads, and indomethacin on the release of IL-1α and IL-1β. PBMC culture supernatants were fractionated by Sephacryl-S-200 column chromatography or HPLC (TSK G3000SW), and each fraction was tested for thymocyte mitogenic activity in the presence or absence of preincubation with anti-IL-1α or anti IL-1β monoclonal antibody (mAb) and for the presence of IL-1α or IL-1β protein by ELISA. In all experiments, thymocyte mitogenic activity not neutralizable by anti-IL-1α or anti-IL-1β mAb was detected in the 25K Mr range, which ranged from 12 to 50% of the total thymocyte mitogenic activity released, depending on the stimuli. Cultured PBMC from 95% of individuals release thymocyte mitogenic activity in the absence of exogenous stimuli, which was increased 1.3- to 7-fold by lipopolysaccharide (LPS) (25–50 üg/ml). All of this increased activity was due to increased release of IL-1β and non-IL-1 thymocyte mitogenic activity, with no change in the total amount of IL-1α released. Indomethacin (0.1 μg/ml) induced release of increased thymocyte mitogenic activity of 1.3- to 1.4-fold over unstimulated cultures. All of this increased activity was due to increased release of IL-1α and non-IL-1 activity with a concomitant decrease in IL-1β release. Interferonγ (40–100 U/ml) increased the amount of IL-1α and decreased IL-1β and non-IL-1 activity released, resulting in no overall change in the total amount of thymocyte mitogenic activity. Molecular weight fractionation of the PBMC culture supernatants revealed that thymocyte mitogenic activity eluting in the 25K Mr range was not due to IL-1α or IL-1β. With certain culture conditions, thymocyte mitogenic activity was detected in the 30–40K Mr range. PBMC cultured with LPS and latex beads in the absence of serum released 30–40K Mr IL-1α, as well as 17K Mr IL-1α and 17K Mr IL-1β. PBMC cultured in 2% fetal calf serum (FCS) alone from some donors released only 30–40K Mr thymocyte mitogenic activity. Both IL-1α and IL-1β protein was detected by ELISA in this Mr range but only the IL-1α was bioactive. This study shows that release of IL-1α, IL-1β, and non-IL-1 thymocyte mitogenic activity can be modulated by different stimuli in consistent patterns, and suggests that the release of these factors is independently regulated.