Recruitment of primitive peripheral blood cells: synergism of interleukin 12 with interleukin 6 and stem cell factor

Abstract

Interleukin-12 (IL-12), a heterodimeric cytokine with potent biological activity, was evaluated for effects on proliferation of human immature progenitor cells in vitro. In vitro proliferation of 5-FU-resistant CD34+ (G0) peripheral blood stem cells (PBSC) in response to sequential cytokine stimulation was examined in the presence and absence of 100 ng/ml IL-12. PBSC were found to include a subpopulation of cells that were resistant to 25 microg/ml 5-FU and required a combination of IL-12, IL-6 and SCF for the production of morphologically recognizable clonogenic elements at day 14 in semisolid medium. Furthermore, addition of IL-6 soluble receptor (IL-6Rs) to IL-6 and SCF led to a similar recruitment. We also demonstrated a significant production of IL-6Rs by CD34+ cells stimulated by IL-12. We noted that glucocorticoids and aldosterone, a mineralocorticoid, had a positive effect on recruitment, but neither mineralocorticoid nor glucocorticoids induced IL-6Rs production by CD34+ cells. The recruitment mechanism by steroids seemed to be different from that used by IL-12. These results confirm previous findings which showed the involvement of IL-12 on immature PBSCs and suggest that IL-12 might play a key role in early haemopoiesis.

Multilevel Regulation of IL‐6R by IL‐6–sIL‐6R Fusion Protein According to the Primitiveness of Peripheral Blood‐Derived CD133+Cells

“…Similarly to another study [24], HSCs constitutively produced sIL‐6R at a basal level (54.8 ± 6.5 pg/ml per 1.5 × 10 5 CD133 + untreated cells for a period of 24 hours) (Fig. 2).…”

“…We opted for a preculture with 5‐FU, which is an antimetabolite that inhibits thymidine synthase and kills all cycling cells. This method has been previously used to select quiescent or slow‐dividing hematopoietic stem/progenitors cells [24, 36–38], which are considered the most primitive cells [35, 39–41]. Cell‐cycle analyses showed that, after 5‐FU pretreatment in the presence of IL‐3, part of the G 0 CD133 + population was recruited and entered apoptosis.…”

“…Altogether these findings suggest that the supportive role of stroma can be partially ascribed both to paracrine and autocrine networks between fibroblasts and HSCs involving IL‐6 and its receptor. It was previously shown by our group that IL‐12 increases the concentration of sIL‐6R in the supernatant of peripheral blood (PB)‐derived CD34 + cells [24], but until now there has been no report devoted to the regulation of mIL‐6R and sIL‐6R on HSCs by gp130 activation. In the present study, we demonstrate that gp130 activation by HIL‐6 stimulates mIL‐6R expression and sIL‐6R production through a post‐translational mechanism involving a disintegrin and metalloprotease (ADAM) protease.…”