Leu 7+ (HNK-1+) cells. II. Characterization of blood Leu 7+ cells with respect to immunophenotype and cell density

Follicular dendritic cells and germinal centers

Follicular dendritic cells (FDCs) are stromal cells unique to primary and secondary lymphoid follicles. Recirculating resting B cells migrate through the FDC networks, whereas antigen-activated B cells undergo clonal expansion within the FDC networks in a T cell-dependent fashion, thereby generating germinal centers. Here, B cells undergo somatic mutation, positive and negative selection, isotype switching and differentiation into high-affinity plasma cells and memory B cells. Since the discovery of FDCs by electron microscopy as long-term antigen-retaining cells 30 years ago isolation of FDCs and generation of FDC-like cells lines and of FDC-specific monoclonal antibodies have been achieved. FDCs express all three types of complement receptors as well as Ig-Fc receptors, through which antigen-antibody immune complexes are retained. However, the mechanism that prevents FDCs from internalizing the antigens and retaining them in native form for long periods of time remains obscure. Substantial evidence derived from cultures in vitro indicates that FDCs contribute directly to the survival and activation of peripheral B cells. The adhesion between FDCs and B cells is mediated by ICAM-1 (CD54)-LFA-1(CD11a) and VCAM-VLA-4. T cells may interact with FDCs in a CD40/CD40-ligand-dependent fashion. Whether FDCs originate from hematopoietic progenitors or from stromal elements is still a controversy. New evidence suggests the presence of two types of dendritic cells within human germinal centers: (i) the classic FDCs that express DRC-1, KiM4, and 7D6 antigens represent stromal cells; and (ii) the newly identified CD3-CD4-CD11c- germinal center dendritic cells (GCDC) represent hematopoietic cells that may be analogous to the antigen-transporting cells described in mice. Finally, FDCs appear to be involved in the growth of follicular lymphomas and in the pathogenesis of HIV infection.

Comparison of NK-cell (Leu-7+ and Leu-11b+) populations in clinically healthy gingiva, chronic gingivitis and chronic adult periodontitis

Various investigations have reported the presence of cytotoxic lymphocyte activity in inflammatory periodontal disease. The collective evidence indicates that the inflammatory infiltrates of gingivitis and periodontitis should feature a major component of large granular lymphocytes (NK-cells) possessing cytotoxic potential. Thus, the purpose of this study was to determine and compare, by use of immunohistochemical methods, the numbers of NK-cells in biopsies of clinically healthy gingiva, chronic gingivitis and chronic adult periodontitis and their relationship, if any, to the T- and B-lymphocyte populations. Gingival biopsies were obtained from 8 patients in each of three disease groups selected on the basis of predetermined clinical criteria. Using the avidin-biotin immunoperoxidase technique, four consecutive serial sections from each biopsy specimen were stained with a panel of antihuman monoclonal antibodies for T-lymphocytes (UCHL-1) B-lymphocytes (CD-45R), and NK-cells (Leu-7 and Leu-11b). Analyses of variance yielded a statistically significant main effect for each cell immunophenotype. The Newman-Keuls Sequential Range Test showed statistically significant differences for all but two mean comparisons (p less than 0.01). The comparisons for UCHL-1 and Leu-7 between chronic gingivitis and periodontitis specimens did not demonstrate significance. Although T- and B-lymphocyte populations increased approximately 20 x progressing from healthy to gingivitis to periodontitis specimens, the NK-cell population showed only a 3 x increase which represented 19%, 6.6% and 7% of the total of all positively stained lymphocytes across biopsy groups.

Inflammatory infiltrates and natural killer cell presence in human brain tumors

Immunohistochemical analysis of subpopulations of inflammatory cells in 81 primary and secondary human brain tumors was done. Natural killer (NK) cells, representing non-major histocompatibility complex-restricted, spontaneous cytotoxicity and monocytic cells are virtually absent in infiltrates of gliomas and account only for a minor percentage of inflammatory cells in brain metastases of carcinoma and in craniopharyngeomas. Infiltrates in gliomas consist almost exclusively of T-cells of the suppressor/cytotoxic type whereas infiltrates in carcinoma metastases and craniopharyngeomas contain considerable numbers of T-helper/inducer cells and B-cells. From this the authors conclude (1) that NK cells do not play a major role in tumor rejection, and (2) that the kind of inflammatory reaction does not depend upon the tumor site but more likely on the tumor type. No correlation between tumor differentiation and infiltrate composition is evident.

Seasonal modulation of the circadian time structure of circulating T and natural killer lymphocyte subsets from healthy subjects

A seasonal modulation of the circadian time structure of circulating T and natural killer (NK) lymphocyte subtypes was documented in five healthy men aged 24-36 yr. Venous blood was obtained every 4 h for 24 h from each subject in January, March, June, August, and November 1984. Three subjects were also studied in April and/or August and/or November 1983 for the T subsets only. Mononuclear cells were isolated on Ficoll-Paque gradient and aliquots were incubated with OKT3, OKT4, OKT8, or HNK-1 monoclonal antibodies for characterizing all, T, T helper, T suppressor-cytotoxic, and NK lymphocytes, respectively, under an epifluorescence microscope. An effect of both sampling time and study month was statistically validated (P less than 0.01) with both two-way analysis of variance and cosinor for the peripheral counts in total, pan-T, T helper, and NK lymphocytes (cells per cubic millimeter). Seasonal changes affected both the circadian patterns and the 24-h mean values. Thus the double amplitude (total extent of variation) of the circadian rhythm in circulating total, T and T helper lymphocytes varied between 0 in March (P greater than 0.30; no rhythm) and up to 46-68% of the 24-h-mean (M) in November, with acrophases (times of maximum, 0) localized in the first half of the night (P less than 0.001). Maximal values were found at 8:30 h for both T suppressor-cytotoxic and NK lymphocytes; a smaller second peak was also found at 20:30 h, and a 12-h rhythm was validated by cosinor (P less than 0.0001), with no patient change in waveform along the year scale. A circannual rhythm was statistically validated by cosinor for total (0 in November), pan-T (0 in March), T suppressor-cytotoxic (0 in December), and NK lymphocytes (0 in October). A rhythm with a period equal to 6 mo was found for circulating T helper cells with 0 occurring both in April and October. Seasonal variations in the incidence of several immunologically related diseases may correspond to an endogenous circannual time structure.

Characterization of two morphologically distinct Leu-7+ cell subsets with respect to Leu-15 antigen. Evaluation of Leu-15 determinant distribution on both E rosetting and non-adherent non-E rosetting cell populations

In the present study the fine structures of Leu-7+-Leu-15+ and Leu-7+-Leu-15- cell subpopulations were characterized by using an immunogold-immunoperoxidase double labelling in electron microscopy. The densities of Leu-15 antigenic sites on both E rosetting (Er) and non-adherent/non-E rosetting (non-A/non-Er) Leu-15 positive cell surfaces were also evaluated by using an immunogold analysis in electron microscopy. A majority of Leu-7+ cells co-expressed the Leu-15 antigen and showed an ultrastructural pattern specific for mature natural killer (NK) cells, i.e. abundant cytoplasm with many organelles, numerous electron dense granules, and irregular outline. On the other hand, a minority of Leu-7+ cells did not express the Leu-15 antigen and showed a clearly different ultrastructural feature in comparison to Leu-7+-Leu-15+ cells. Thus, the presence of the Leu-15 antigen on Leu-7+ cell surface corresponds to ultrastructural features specific to differentiated NK cells and may represent an expression of Leu-7+ cell differentiation. An alternative hypothesis may be that Leu-7+-Leu-15+ and Leu-7+-Leu-15- cells represent distinct cell lineages within non-A/non-Er Leu-7+ cells. Finally, the results of the present study provide proof that Leu-15 antigen is more frequently represented on non-A/non-Er Leu-15+ cells than on Er Leu-15+ cells.

Leu 7+ (HNK-1+) cells. I. Selective compartmentalization of Leu 7+ cells with different immunophenotypes in lymphatic tissues and blood

In the present immunohistochemical studies, Leu 7+ (HNK-1+, human natural killer and killer) cells were found to occupy preferentially germinal centres of follicles in lymph nodes and tonsils. Leu 7+ cells were also present in germinal-like zones of spleen follicles and in mantle zones of hyperplastic thymus follicles and varied in localization in lymph nodes involved in different types of follicular centre cell-derived malignant lymphomas. Most of the Leu 7+ cells in the follicles expressed the Leu 3 (helper/inducer) marker. Double staining studies of tonsil sheep erythrocyte-rosetting and peripheral blood mononuclear cell suspensions showed that two main, mutually complementary, subpopulations of Leu 7+ cells could be distinguished in both cases, namely Leu 7+/Leu 4+ (subdivided into Leu 2+ (suppressor/cytotoxic) and Leu 3+) and Leu 7+/Leu 4-, including mostly cells with OKM 1 (myelomonocytic) characteristics. Thus, in the tonsil cell suspension the cells with Leu 7+ Leu 3+/OKM 1- immunophenotype strongly predominated, whereas among peripheral blood mononuclear cells Leu 7+Leu 2+/OKM 1- and Leu 7+/OKM 1+ immunophenotypes were mostly observed.