Stromal cells in bone marrow were described by Friedenstein et al.
in 1990, as cells that proliferate from colonies and have spindle shape. They can
differentiate into many cell types that could be present in many different
tissues such as: osteoblasts, adipocytes, chondroblasts, ets. under specific in
vitro conditions attached to plastic flasks. These cells that are later obtained
from postnatal bone marrow are called stromal stem cells or mesenchymal stem cells
(MSC). It has been demonstrated that the presence of similar cells in many other
tissues as well, despite the extensive attempts to characterize these cells, the
definitive in vivo markers of MSC are still unknown. Although, the demonstration
of functional data that support that common adult stem cells exist and have the
ability to differentiate with several specific differentiation lineages.

Because MSC could be easily isolated
from bone marrow and could be prolonged in vitro, they became a prime
target for tissue regeneration for researchers. They are now broadly used in many
experiments and transplantation in animals and some human therapeutic trials. But,
more new research is required to learn more about the molecular mechanisms of
the differentiation of MSC to estimate the full capacity for tissue regeneration
(Vaananen, H.; 2005).


Based on their ability for immune response suppression, they are
used to study regenerative medicine. They have paracrine effects which includes
immunomodulation occurring by the secretion of soluble mediators, that includes
human leukocyte antigen G5, transforming growth factor-beta and nitric oxide. In
bone marrow, MSCs regulate immunological memory by the recognition of defined amounts
of specialized niches for memory T cells and plasma cells in the bone marrow
and are contacting with T and B cells to do so. All stromal cells probably
share all of these biological effects, which includes stem cells that are isolated
from exfoliated deciduous teeth and fibroblasts. (Yamaza T. et al.; 2010).


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