Karen L. Imfeld

Expression of cytokines by multipotent neural progenitor cells

Recent work with mammalian neural stem cells has highlighted the role of cytokine signaling in the proliferation and differentiation of these multipotent cells. While the responsiveness of neural progenitors to exogenously applied growth factors has been demonstrated in vivo as well as in vitro, little attention has been given to the production of cytokines by these cells. Here we use immunocytochemistry, RT-PCR, and ELISA to show that under standard growth conditions multipotent neural progenitor cells from humans express multiple cytokines including IL-1alpha, IL-1beta, IL-6, TGF-beta1, TGF-beta2, TNF-alpha, but not IL-2, IL-4, or IFN-gamma. Neural progenitor cells from rat and mouse express some, but not all, of these cytokines under similar conditions. While the function of cytokine expression by neural progenitor cells remains to be elucidated, these signaling molecules are known to be involved in neural development and may play a role in the activation of quiescent stem cells by a variety of pathological processes.

The immunological properties of adult hippocampal progenitor cells

Adult hippocampal progenitor cells (AHPCs) derived from mature rats were studied in mixed co-cultures and shown not to elicit a proliferative response from human peripheral blood mononuclear cells (PBMCs) or allogeneic spleen cells. FACS analysis revealed low class I and no detectable class II (Ia) MHC expression by these cells. RT-PCR showed that AHPCs express the anti-inflammatory cytokine TGF-beta1. AHPCs did not, however, significantly impede the proliferation of OKT3- or PHA-stimulated PBMCs. Taken together, these results indicate that AHPCs are non-immunogenic in vitro. This is consistent with their pattern of MHC expression and does not require an active immunosuppressive mechanism.

Modulation of IL-1 alpha, IL-1 beta, and 25K Mr non-IL-1 activity released by human mononuclear cells.

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.

Tissue Factor Inflammatory Response Regulated by Promoter Genotype and p38 MAPK in Neonatal vs. Adult Microvascular Endothelial Cells

Objective and designVariable tissue factor (TF) expression by human microvascular endothelial cells (HMVEC) may be regulated by two promoter haplotypes, distinguished by an 18-basepair deletion (D) or insertion (I) at −1,208. We sought to determine the relationship between these haplotypes and interleukin-1α (IL-1α)-induced TF expression in neonatal versus adult HMVEC.ResultsIL-1-stimulated TF mRNA, protein, and activity were significantly higher in neonatal compared to adult D/D donors. IL-1-stimulated HMVEC from neonatal D/D donors expressed threefold higher levels of TF mRNA, twofold higher TF protein, and fourfold increased TF activity compared to HMVEC from adult D/D donors. These results indicate that homozygosity for the D haplotype is characterized by increased response to IL-1 in neonates, but not adults. IL-1 induced increased phosphorylation of p38 mitogen-activated protein kinase (MAPK), which was significantly greater in neonatal compared to adult HMVEC. Moreover, inhibition of the p38 MAPK pathway reduced IL-1-stimulated TF mRNA expression in D/D neonatal but not adult HMVEC.ConclusionsUpregulation of D/D neonatal HMVEC TF expression by IL-1 is mediated through the p38 MAPK pathway. This heightened response of D/D neonatal HMVEC to inflammatory stimuli may contribute to increased microvascular coagulopathies in susceptible newborn infants.