Characterizing a soluble survival signal for activated lymphocytes from CD14⁺ cells

Abstract

SUMMARYT-cell activation requires at least two signals: antigen and a costimulatory signal. As antigenpresenting cells play an important role in this area, the role of CD14+ cells in T-cell activation, proliferation and activation-induced cell death (AICD) was investigated. Using phytohaemagglutinin (PHA) activation, it was found that CD14 + cell depletion resulted in significantly greater AICD, decreased lymphocyte growth and up-regulated interleukin-2 (IL-2) secretion. However, T-cell activation was delayed according to the expression of CD69 and CD25. Dynabeads conjugated with anti-CD14 monoclonal antibody (mAb) bound CD14 + cells and induced secretion of IL-1b, tumour necrosis factor-a (TNF-a), transforming growth factor-b (TGF-b) and IL-6, but not IL-2, IL-12 or IL-15. Supernatants were collected from Dynabeads-activated CD14 + cell cultures and designated as 'CD14 cocktails'.Addition of CD14 cocktails to CD14 + cell-depleted mononuclear cell cultures reversed the increased AICD, decreased lymphocyte growth and increased IL-2 secretion. Depletion of IL-1b and TNF-a in the CD14 cocktails by panning followed by blocking with the corresponding mAbs had no effect on the active AICD protection. TGF-b was determined not to be the active factor owing to the presence of >1 . 0 ng of TGF-b in the media for culturing both CD14 + and CD14 x peripheral blood mononuclear cells (PBMC). The CD14 cocktails did not contain IL-12 and IL-15. Depletion of IL-6 with panning followed by blocking residual IL-6 with anti-IL-6 mAb significantly reduced the protective effect of the CD14 cocktails. Human recombinant IL-6 also partially reversed the effects of CD14 + cell depletion on AICD, lymphocyte growth and IL-2 secretion. The data suggest that IL-6 is one of the active factors in the survival signal from CD14 + cells.

Survival Factors from Activated Accessory Cells and their Role in Triggering Autoimmune Diseases

“…Depletion of IL-6 followed by blocking residual IL-6 with anti-IL6 mAb significantly reduced the protective effect of the CD14 cocktails. In addition, human recombinant IL-6 also partially reversed the increased apoptosis in the activated lymphocytes predepleted of CD14+ cells [20]. We also found that the antiapoptotic effect of IL-6 correlates with the suppression of IL-2 secretion, which is in contrast to a previous report showing that IL-6 inhibits apoptosis but not IL-2-induced activation [27].…”

“…It was shown that IL-27 could limit IL-2 production by preventing down-regulation of the suppressor of cytokine signaling 3 (SOCS3) in activated lymphocytes [205][206][207]. Given that the CD14 cocktails found in our system also down-regulate IL-2 secretion and that down-regulation of IL-2 secretion correlates with the suppression of AICD [20], one can speculate that IL-27 may have an anti-apoptotic function and enhance survival of activated T lymphocytes as well. In addition, the similarity of IL-27 receptor subunits to IL-12 and IL-6 may also implicate their possible shared functionality (Fig.…”

“…We observed increased AICD in the activated lymphocytes after depletion of CD14+ cells (human monocytes) in both the control healthy subjects and RA patients [20,21]. Interestingly, the AICD rate was much higher in CD14+…”

“…However, not all activated monocytes secrete IL-12. Cross-linking of CD14 molecules on human monocytes does not induce IL-12 secretion [20]. IL-12 production is positively regulated by IFN-γ that IL-12 itself induces [146,159,160].…”

Increased activation‐induced cell death in peripheral lymphocytes of rheumatoid arthritis patients: the mechanism of action

“…Recently, we reported that activated CD14 + cells secrete a soluble survival signal (CD14 cocktail) that protects activated lymphocytes from undergoing AICD 33 . In this study, we investigated further a possible role of the soluble survival signal in supporting outgrowth of T lymphocytes in RA patients.…”