CD34-positive developing vessels and other structures in human fetuses: an immunohistochemical study.

CD34 is a well-known marker of progenitor cells of blood vessels and stromal tissues. Thus, CD34-positive cells have recently been used clinically in the field of vascular and orthopedic biotechnology because of their capacity to assist regeneration of injured tissues. However, to our knowledge, the in situ distribution of CD34-positive cells has not yet been described in the human fetus, with the exception of a few organs. In the present study, we conducted immunohistochemistry for CD34 using 12 human fetuses (9-15 weeks of gestation). CD34-positive structures showed a vessel-like appearance and were regularly arrayed in the viscera, nerves and lymph nodes, whereas in the body wall and extremities, they were distributed diffusely as fibrous tissues, such as the fascia and perimysium. The myocardium was also divided and bundled by CD34-positive fibrous tissues. In striated muscles, limited examples of CD34 expression were found in the tongue and extraocular muscles in which only vessels were positive. Lymphatic vessels were negative for CD34. In addition to their contribution to vascular development in any part of the body, CD34-positive mesenchymal tissues seem to play a critical role in the pattern formation of skeletal muscle, synovial tissue and other muscle/tendon-associated tissues in human fetuses.