Immunocytes in the human fetal pancreas--a contribution to developmental immunoendocrinology concerning diabetes mellitus and organ cultivation.

The studies were performed on 103 samples of human fetal pancreas tissue (10th to 26th week of gestation). Of the mothers, 14 had insulin dependent type I diabetes mellitus (IDDM), and 33 of the samples were examined before and after cultivation for 14 days. 3 samples taken from fetuses in the 14th week of development (mothers without metabolic disorders) were examined in the electron microscope. Lymphocytes are generally irregularly distributed within the tissue. Groups of 3 to 5 lymphocytes are found in addition in the 12th week of development, and larger clusters (10 to 15 lymphocytes) appear from the 14th week onward. Relating these quantitative results to the 3 phases of early fetal islet organ development, it can be seen that lymphocyte numbers increase from the 10th to the 26th week of development. The significance of this is discussed in connection with the development of the immune system. In view of the contemplated transplantation of fetal pancreas tissue as treatment for IDDM, it means that a relatively low immunogenicity can be expected up to the 14th week of development. Thymic differentiation is not complete before the 17th week, and differentiation of the lymph nodes and spleen continues until weeks 20 to 23. Although IgG antibodies are transferred across the placental barrier already in about the 8th week, this flux does not reach its maximum until the 32nd week. Endogenous antibody synthesis in the fetus does not start until the 18th week. IDDM of the mother during fetal development (10th to 26th week) does not increase the lymphocyte number in the pancreas. This also applies to tissue that has been cultivated for 14 days after reaching the same stage of development.