Cytokine secretion by hUCB-derived mononuclear cells – a putative mediator of functional improvement after hypoxic-ischemic brain lesion?

Intraperitoneal transplantation of human umbilical cord blood-derived mononuclear cells led to the “homing“ of these cells specifically to a hypoxic-ischemic lesion in perinatal rats. Motor deficits resulting from the lesion were alleviated upon transplantation (1). However, the molecular and cellular mechanisms underlying the functional improvement are still unclear. As neuronal differentiation of transplanted cells seems to be a rare or absent event in vivo, we propose secondary mechanisms, which might be responsible for the therapeutic effects. One possibility is that transplanted cells might contribute to a regenerative environment by secretion of cytokines.

Using a succession of distinct culture media, mononuclear cells were stimulated by growth factor combinations, i.e. epidermal growth factor/fibroblast growth factor-2 or nerve growth factor/retinoic acid, and analyzed immunocytochemically. Conditioned medium was collected at various time points (2, 7, and 14 days of cultivation) and subsequently assayed for levels of secreted cytokines.

HUCB-derived mononuclear cells in culture responded to growth factor treatment with proliferation, as assessed by detection of the Ki-67 protein. In addition, neural differentiation was initiated, demonstrated by expression of neuronal and glial marker proteins. Most importantly, in response to either growth factor combination, cells were shown to secrete various cytokines. Significant levels of cytokines were detected for proteins of the interleukin (Il) family (Il-1beta, -6, -7, -8, -10), growth factors (PDGF, EGF, HGF) as well as chemokines (MCP-1, MIP-1beta, Eotaxin).

Most factors present in conditioned medium are renowned for their anti-inflammatory, neuroprotective, angiogenic, or chemotactic action. These results are promising in that secreted cytokines of human mononuclear cells might be suitable candidates mediating functional recovery after hypoxic-ischemic brain injury.

(1) Meier et al. (2006) Pediatr. Res. 59:244–249