Advances in molecular biological procedures, bioinformatics and transgenic technology and their rapidly broadening use hive led to an immense increase of data concerning the cells comprising the immune system at molecular level. This new knowledge is mostly relevant to the hemopoietic components of structured lymphoid tissues, while similar research efforts aimed at investigating the non-hemopoietic stromal parts have until recently been rather neglected. However, the results of recent investigations have established the importance of tissue differentiation and functional maturation of these latter components within the lymphoid organs during the embryonic development for achieving the individual's immunological competence, as manifested in various forms of immune responses. Research performed on murine embryos have revealed the origin and developmental pathways of these less investigated stromal components, identified the molecular participants involved in their interactions with lymphoid cells, and determined the anatomic location of lymphoid-stromal domains and the sequence of interactions between the two tissue partners. In addition to the obvious theoretical importance of the above events, their resemblance to the occurrence of certain pathological conditions with inflammatory origin has also become apparent, where the course of the disease is characterized by the formation of "tertiary lymphoid tissue" in the affected organ. A more detailed understanding of the dependence of hemopoietic cells on their stromal environment in the lymphoid tissues may offer support for establishing a more efficient causal therapy for chronic inflammations. The purpose of the present account is to report these developmental events, and to emphasize the importance of the stromal development and functional dynamics during the interpretation of immune functions and place them at least as important a diagnostic and therapeutic target as the current clinical evaluation hitherto mainly focussed on lymphoid cells. Familiarity with this aspect of lymphoid tissue formation through the appreciation of the rols played by stromal mesenchyma may also arouse interest for exploring more efficient treatment modalities for diseases with relevant immunopathogenesis.
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