Leu 7 monoclonal antibody and immunohistochemical technic were used to study the distribution of NK cells in human lymph node, tonsil, spleen and thymus. The results indicated that the NK cells predominately distributed in B cell area, such as germinal center of secondary follicle, which occured in lymph node and tonsil. A few NK cells were found in the paracortex and medulla of lymph node. In the spleen, the NK cells mainly located in the germinal center of splenic nodules and in the periphery of white pulp. However, the NK cells were never shown in the perarterial lymphatic sheath, some NK cells also scattered in the pulp cord and sinuses of red pulp. In the thymus, the NK cells were restricted in the medulla, and the number of NK cells reduced in the aged thymus. In addition, the Leu 7 antibody was reacted with epithelial cells, which located in the cortical periphery or thymic lobule. The morphology of NK cells in different lymphoid organs was similar. The staining intensity of Leu 7 antibody was identical both in the frozen and paraffin sections.

9 fetal and 7 juvenile thymuses were used to identify the asteroid cells on the frozen sections by immunohistochemical method. The results indicated that the thymic medulla, except B cells, contains a type of larger cells with small cytoplasmic processes, which has in common with B cell antigens, such as 1gM, 1gA, Leu14, BA-1, HLA-DR and light chain-Kappa, but they do not express OKB-2. Moreover, the asteroid cells do not reactive with T cell antibody and follicular dendritic cell antibody, and lack of ANAE activity. The asteroid cells in the fetal thymus are constantly located in the corticomedullary region, while, in the juveniles, the asteroid cells are mainly distributed within medulla or in the vicinity of Hassall's corpuscles. As regards the function of asteroid cells is not clear. Based on their distribution, it is probably associated with T cell maturation. On the morphologic ground, the asteroid cells are similar to interdigitating cells in thymus, the relationship between them has been discussed.