Morphological, immuno- and lectinohistochemical evaluation of the lymphoid apparatus of the human fetal appendix

Abstract

Aim. To identify the morphological and functional features of the human appendix lymphoid formations in the late period of prenatal ontogenesis. Materials and methods. The vermiform appendices from 42 human fetuses of both sexes without anomalies, diseases of the gastrointestinal tract, immune system and hematopoiesis were examined. Histological, lectinohistochemical (PNA+, SBA+), immunohistochemical (expression of markers CD3+, CD4+, CD8+, CD20+, CD34+, CD68+, Ki-67, caspase 3+), morphometric methods of examination were used with statistical analysis of the obtained results. Results. Single lymphocytes are seen near venules in the mucous membrane of the human fetal vermiform appendix at 16–18 weeks’ gestation; the lymphocytes are aggregated to form the lymphoid follicles at the 25th week. The lymphoid follicles are populated by small- and medium-sized lymphocytes, macrophages, cells at the stages of apoptosis (Caspase 3+) and proliferation (Ki-67+), reticular cells. From the 28th week of the prenatal period, lymphoepithelial nodules are detected compositionally resembling perivascular ones. In the subepithelial and peripheral zones of the nodules, there are lymphocytes expressing CD3 and PNA receptors, in the central zone – CD20 and SBA receptors, macrophages (CD68+/PNA+/SBA+), cells at the stage of proliferation (Ki-67+) and apoptosis (caspase 3+). By the end of the fetal period, the lymphoid follicles of the human appendix contain fewer T-lymphocytes (CD3+) and an increased number of B-lymphocytes (CD20+) and macrophages (CD68+), which are localized mainly in the central zone, however, the germinal centers are not yet formed. Conclusions. In the developmental process of the vermiform appendix lymphoid tissue during the prenatal period of ontogenesis, the following critical periods were noted: the 16th–18th weeks – the appearance of lymphocytes in the lamina propria, the 25th week – the formation of perivascular lymphoid follicles near venules, the 28th week – the appearance of lymphoepithelial nodules. The number of T-lymphocytes (CD3+) was decreased in the lymphoid follicles, while the number of B-lymphocytes (CD20+) and macrophages (CD68+) was increased with age.