N-linked oligosaccharides can protect target cells from the lysis mediated by NK cells but not by cytotoxic T lymphocytes: role of NKG2-A.

We have previously shown that glycophorin A (GPA), inserted by electropulsation into the membrane of K562 cells, protected them from natural killer (NK) cell-mediated cytotoxicity and the unique N-linked oligosaccharide of GPA was essential for resistance to occur. The present study demonstrates that the protection level conferred by GPA is similar to the resistance induced by HLA-Cw3 expressed by transfected K562 cells. A monoclonal antibody against NKG2-A, an NK inhibitory receptor interacting with HLA class I antigens and belonging to the C-type lectin receptor, was able to restore the ability of NK cells to lyse K562 cells expressing HLA-Cw3 at the cell membrane but not electroinserted-GPA, suggesting that the N-linked oligosaccharide of GPA cannot be a ligand for NKG2-A. GPA was then electroinserted into the membrane of two lymphoblastoid B-cell lines: one was sensitive to NK cell-mediated lysis, the other was susceptible to cytotoxic CD8+ T-lymphocyte (CTL)-mediated cytotoxicity. The electroinserted GPA protected the target cells from NK-mediated cytotoxicity, whereas it did not modify the cell susceptibility to lysis by CTL. Endoglycosidase F treatment abolished the resistance towards NK cell-mediated lysis, suggesting that N-linked glycans could inhibit mechanisms used by NK cells to exert their cytotoxic function in agreement with our previous results.

Flow cytometric characterization of proliferating natural killer lymphocytes from bone marrow donors in the mixed lymphocyte reaction.

Detection of natural killer (NK) cells in the mixed lymphocyte reaction (MLR) was investigated by flow cytometry and cytotoxicity toward the K562 cell line. Peripheral blood mononuclear cells (PBMCs) from normal individuals were stimulated with either lymphoblastoid cell lines (LCLs) or PBMCs. This approach allowed the following observations: 1) after stimulation by LCLs, the percentage of NK cells increased concomitantly with the level of cytotoxicity, in contrast to when PBMCs were used as stimulators; 2) anti-interleukin-2 monoclonal antibody strongly inhibited NK proliferation in the MLR, but antibody to interferon gamma did not; and 3) purified NK cells were unable to proliferate against LCLs. All these data suggest that NK cells induced by LCL stimulators depend on T cells to proliferate in the MLR. Flow cytometric detection of NK cells in the MLR was also used on cryopreserved PBMCs from 31 bone marrow donors, because it has been reported that an enhanced donor NK cell activity was correlated with the development of graft-versus-host disease after HLA-identical sibling bone marrow transplantation. NK cell proliferation under LCL stimulation was intense and varied greatly among the donors tested. However, no statistical correlation was observed between LCL-induced donor NK cell proliferation in the MLR and the occurrence of graft-versus-host disease after bone marrow grafting.

Characterization of lymphocyte subpopulations in periapical lesions by flow cytometry.

The mechanisms by which the bacterial root-canal infection leads to periapical bone destruction (cysts or granulomas) are not yet well understood. Previous works have shown elements of an active immune response in the lesions. In the present study, flow cytometry was used to improve the characterization of immune cells. Semiquantitative immunohistochemical analysis showed the presence of plasma cells, macrophages and B and T cells. The simultaneous use of several antibodies in flow cytometry allowed a more precise phenotype of the lymphocytes. The cysts displayed an abundance of B lymphocytes at the same time as a relative scarcity of CD8+ cells. CD4+ lymphocytes were the dominant lymphocyte population in most cases. A small number of gamma delta T lymphocytes and natural killer cells was found. These preliminary results show that flow cytometry may be used to characterize immune cells from inflamed tissue and opens the possibility for further functional studies.

Dominant clones in immortalized T-cell lines from rheumatoid arthritis synovial membranes.

Transformation of human T cells by herpesvirus saimiri allows the production of an unlimited number of T cells which express a functional T-cell receptor. In this study we transformed four T-cell lines derived from rheumatoid arthritis synovial membranes. The transformed T cells were mainly CD4+ and expressed the phenotype of activated T cells. They were grown for more than 1 year in the absence of mitogen or feeder cells, and three of them could be maintained without exogenous IL-2. The presence of viral DNA in the transformed cells was shown by in situ hybridization with a probe from the H-DNA region of the virus. No infectious virus could be recovered from the transformed cells. The relative proportion of the 24 different Vbeta families between the four transformed lines showed variations that increased with time. In the two T-cell lines transformed at an early stage of culture, the Vbeta2 family was maintained at about 10%. The dominant Vbeta2 clones that previously have been characterized in the patient were found in all transformed T-cell lines. We have thus shown the feasibility of obtaining transformed T cells from synovial membranes. They contain the dominant clones that are considered of potential importance for the disease, permitting further functional studies.

Specific genetic variants of Actinobacillus actinomycetemcomitans correlate with disease and health in a regional population of families with localized juvenile periodontitis.

A geographically homogeneous population of 83 subjects, from 21 families with localized juvenile periodontitis (LJP), and 35 healthy control subjects was monitored, over a 5-year period, for the presence of the periodontal pathogen Actinobacillus actinomycetemcomitans. Restriction fragment length polymorphism (RFLP) analysis was used to monitor the distribution of genetic variants of this bacterium in LJP-susceptible subjects that converted from a healthy to a diseased periodontal status. A. actinomycetemcomitans was cultured from 57% of the LJP family members accessioned into the study. Nine of 36 LJP-susceptible subjects, in seven families, developed signs of periodontal destruction. All but one of these conversion subjects harbored A. actinomycetemcomitans. Bacterial variants representative of a single RFLP group (II) showed the strongest correlation with conversion (P < 0.002). Six of nine conversion subjects were infected with A. actinomycetemcomitans from this group. RFLP group II variants also prevailed in 8 of 22 probands but were absent in the 35 healthy control subjects. In contrast to the selective distribution of group II variants is diseased individuals, variants belonging to RFLP groups XIII and XIV were found exclusively in the control subjects. Thus, the use of RFLP to type clinical isolates of A. actinomycetemcomitans has resulted in the identification of genetic variants that predominate in LJP and health. These results indicate that studies concerned with the pathogenicity of this bacterium in LJP should be focused on the group II variants.