Natural Killer Cells in Connective Tissue Disorders

Cystic lung lesions in Sjogren syndrome: analysis of lymphocyte subsets in tissue with clinico-radiologic-pathologic correlation

Pulmonary complications associated with Sjögren syndrome (SS) have attracted attention in recent years. Sjögren syndrome has been associated with small cyst formation in salivary glands, thymus, and lungs and has been recently brought to the forefront by radiologists due to high-resolution techniques. However, pathologists are less aware of this finding unless clinico-radiologic-pathologic correlation is sought. Formation of large bullae in SS is a rare complication with potential for confusion with other diseases. Here, we present the clinical, radiologic, and pathologic findings in 3 patients with SS associated with multiple pulmonary cystic lesions. All 3 patients had a variable mixed restrictive and obstructive component of the disease. There was good correlation with the pulmonary function tests (PFTs), high-resolution computed tomographic scan, and morphology with regard to the restrictive component. The small cysts appear to correlate with the extent of obstructive changes on the PFTs. However, the large bullae do not, implying noncommunication with the conducting airways. This noncorrelation between the PFTs and extent of bullous disease with predominant involvement of lower lobes in SS enables distinction from bullous emphysema. The mechanism of bulla formation in SS appears to be different from bullous emphysema. A check valve mechanism has been proposed previously in SS, which does not explain cyst formation in the thymus. Alternately, inflammation may play a role with the key suspects being CD4 T-helper cells and perhaps NK cells. This is the first report of a clinico-radiologic-pathologic correlation with analysis of lymphocyte subsets.

NK cells in autoimmunity: a two-edg'd weapon of the immune system

Natural killer (NK) cells are part of the innate-immune system and respond rapidly to a variety of insults via cytokine secretion and cytolytic activity. Their main function is first line of innate immunity across viral, bacterial and parasitic infections. NK-cells are not solely killers but can also act as regulators of adaptive immunity. It is evident from literature that NK-cells are deeply involved in autoimmunity, but the question is how and why they act as a two edged weapon. Number of circulating NK-cells can be frequently altered depending on the disease taken into consideration. Cytokine milieu, the microenvironment in which they mature and other stimuli acting on different cell surface receptors may differently trigger NK-cells response and influence their role in autoimmune diseases. Functional differences between NK-cells at different anatomical sites, the adaptability of NK-cells effector responses and genetic factors may also explain differences in such responses. Thus, NK-cell alterations may be associated with increased autoimmunity and the modulation in the number of circulating NK-cells seems to be a primary event rather than an active inflammation/drug administration consequence during inflammatory/autoimmune processes, playing a fundamental role in the pathogenesis of a number of autoimmune diseases.

Lymphocyte subsets in peripheral blood of patients with moderate-to-severe versus mild plaque psoriasis

In several studies peripheral blood T-cells have been quantified, yet few data are available on lymphocyte subsets in moderate-to-severe psoriasis (in terms of extent and activity of lesions) versus mild psoriasis. The objective is to compare lymphocyte subsets in peripheral blood of patients with moderate-to-severe disease (PASI-score ≥12) to patients with mild disease (PASI-score <12) and to healthy subjects. By means of flow cytometry method, lymphocytes in peripheral blood of 27 patients with psoriasis and 10 healthy controls were characterized. The absolute number of total lymphocytes was markedly decreased in patients with moderate-to-severe psoriasis as compared to patients with mild disease and normal subjects. Cellcounts of all analysed subsets were found to be increased in more severe psoriasis, except for CD8+CD45RO+ cells. The under-representation of CD8+CD45RO+ cells is compatible with the dynamics of acquired immunity, which requires a time log after the relapse of the lesions to differentiate from CD45RA+ naive cells.

Decreased DAP12 expression in natural killer lymphocytes from patients with systemic lupus erythematosus is associated with increased transcript mutations

Decreased numbers of natural killer (NK) cells and impaired NK function have been reported in patients with systemic lupus erythematosus (SLE). Since DAP12 plays a pivotal role in activation of NK cells, we analyzed the expressions of DAP12 protein and mRNA in peripheral blood NK cells from patients with SLE. Both DAP12 protein and mRNA expressions in NK cells from the SLE patients were decreased compared with those in NK cells from normal subjects. Sequence analysis of DAP12 cDNA showed increased nucleotide mutations, including both nucleotide substitutions and deletions. In spite of the mRNA mutations, we found no mutations in genomic DNA, suggesting that mRNA was modified during or after transcription. Decreased expression of DAP12 in NK cells from the patients was accompanied by increased expression of ADAR1 (adenosine deaminase that acts on RNA transcripts) and by decreased expression of NKp44. These results suggest that abnormal expression of DAP12 molecules in NK cells may account for the impairment of NK cell function in patients with SLE.

Expansion and enhanced survival of natural killer cells expressing the killer immunoglobulin-like receptor KIR3DL2 in spondylarthritis

OBJECTIVE

The spondylarthritides (SpA) are strongly associated with possession of HLA-B27. We hypothesized that the expression of abnormal forms of HLA-B27 in SpA may have a pathogenic role through interaction with cells bearing natural killer (NK) receptors, in particular, killer immunoglobulin-like receptor (KIR) KIR3DL2, a receptor for HLA-B27 homodimer (B27(2)). We therefore undertook the present study to determine the number and function of NK and T cells bearing KIR3DL2 in SpA.

METHODS

Expression of KIR3DL2 on NK and T cells was quantified in peripheral blood (PB) from 35 patients with SpA and 5 patients with juvenile enthesitis-related arthritis (juvenile ERA); samples were compared with samples from healthy and rheumatoid arthritis (RA) controls. Paired synovial fluid (SF) was studied where available. Expression of other KIRs as well as activation, memory, and homing markers on KIR3DL2+ NK and T cells was quantified. NK cell survival was assessed using the apoptotic markers annexin V and 7-aminoactinomycin D, and cytotoxicity by (51)Cr release assay.

RESULTS

In SpA, an increased number of PB and SF NK and CD4+ T cells expressed the KIR3DL2 receptor compared with controls. In ERA, KIR3DL2 expression was increased in PB and SF CD4 T cells (and SF NK cells) compared with RA controls. KIR3DL2+ NK cells had an activated phenotype, and were protected from apoptosis by culture with a cell line expressing B27(2). SpA PB mononuclear NK cells from SpA patients showed greater cytotoxicity than those from controls.

CONCLUSION

KIR3DL2 expression on NK cells and CD4 lymphocytes is increased in SpA and ERA. These cells are activated and may have a pathogenic role.

Detection of autoantibodies to killer immunoglobulin-like receptors using recombinant fusion proteins for two killer immunoglobulin-like receptors in patients with systemic autoimmune diseases

OBJECTIVE

To investigate the existence of autoantibodies to killer immunoglobulin-like receptors (KIRs), especially p58.1 (KIR2DL1) and p58.2 (KIR2DL3), in patients with systemic autoimmune diseases.

METHODS

Sera from 30 patients with systemic lupus erythematosus (SLE), 30 patients with rheumatoid arthritis (RA), 22 patients with Behçet's disease, and 20 healthy control subjects were tested for anti-p58.1 and anti-p58.2 antibodies by Western blot analysis using recombinant p58.1 and p58.2 proteins. Furthermore, clinical features and laboratory data were compared between the anti-p58.1/58.2 antibody-positive and -negative patients.

RESULTS

Anti-p58.1 antibodies were detected in 7 (23.3%) of the 30 patients with SLE, 9 (30%) of the 30 patients with RA, and 6 (27.3%) of the 22 patients with Behçet's disease. Anti-p58.2 antibodies were detected in the same 22 patients who were positive for the anti-p58.1 antibodies. None of the serum samples from the healthy donors were positive for antibodies to the recombinant p58.1 or p58.2 molecules. Compared with the anti-p58.1/ 58.2 antibody-negative patients, the anti-p58.1/58.2 antibody-positive patients had significantly elevated levels of serum IgG in all 3 diseases tested, an accelerated erythrocyte sedimentation rate in RA and SLE, and decreased white blood cell counts in RA.

CONCLUSION

This report is the first to describe the presence of autoantibodies to KIR2DL (p58.1 and p58.2) in the sera of patients with systemic autoimmune diseases. Considering the correlation with several clinical features, these autoantibodies may be involved in the pathologic process of the autoimmune diseases.

Lack of NK cells in lupus patients with renal involvement

We have previously shown that patients with SLE have significantly lower percentages and absolute numbers of NK(CD3-/CD16+56) cells in their peripheral blood compared with normals. Patients with active disease had very low levels of NK cells and the reduction was also associated with patients who had renal involvement. We have now performed a serial study immunophenotyping 11 patients with SLE and renal involvement using dual colour immunofluorescence and flow cytometry. Patients were tested every three months on an average of three occasions. As a control, nine SLE patients without renal involvement were immunophenotyped for similar intervals; 11 normal controls were also tested. Major lymphocyte subsets (T, B and NK) remained very stable during serial bleeds. However, the NK cell populations were decreased significantly in patients with renal involvement both as percentages (5 +/- 6 vs 9 +/- 5, P < 0.0001) and absolute counts (75 +/- 108 vs 109 +/- 52, P < 0.001) in comparison to non-renal patients. Analysis of disease activity using BILAG score showed an inverse correlation between renal system activity and percentage and absolute number of NK cells (P < 0.002 and 0.01, respectively). In this study we have also analysed a CD8 T cell subset which we have not studied before. We have found a significantly increased percentage of CD38+CD8+ T cells(activated CD8 subset) in patients with SLE in comparison to normal controls. We did not find any association with the CD38+CD8+ T cells and disease activity as measured by BILAG or renal involvement. NK cells are important factors in immunity against virus infections and tumour cells. CD38+CD8+T cells are increased in viral infections. We speculate that the lack of NK cells in SLE patients might have an association with increased CD38 expression.

Reversal of lovastatin-mediated inhibition of natural killer cell cytotoxicity by interleukin 2

The activation of human natural killer (NK) cell cytotoxicity by interleukin 2 (IL-2) is well established, although the biochemical mechanisms of this stimulation have not yet been fully delineated. Earlier, we reported that treatment of NK cells with an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase such as compactin or lovastatin significantly abrogates the in vitro killing of a susceptible human erythroleukemic cell line and that this inhibition can be completely reversed by 2 hr of exposure to mevalonate (J. Cell. Physiology 139:550-557, 1989). We report here that 24 hr of treatment with IL-2 also reverses lovastatin inhibition of NK cell function. In addition to natural cytotoxicity, IL-2 also restores chemotactic and antibody dependent cellular cytotoxicity functions to lovastatin-treated cells. IL-2 does not stimulate proliferation of these cells during this time period, nor does it affect the phenotypic composition of the NK cell preparations. Although IL-2 was able to reverse the lovastatin-mediated inhibition of every cell function we examined, it had no effect on the inhibition of cholesterol biosynthesis as measured by [3H]acetate incorporation into non-saponifiable lipids, nor did it stimulate HMG CoA reductase activity. These findings support the hypothesis that there is a non-sterol isoprenoid product which is required for NK cell cytotoxicity and chemotaxis. In addition, the data suggest that IL-2 stimulation of NK cells proceeds by an isoprenoid-independent pathway.

Natural killer cells and autoimmunity

In various autoimmune diseases it appears that NK activity is impaired, and that this phenomenon is significant in disease development. Impairment of NK activity may be the result of two different mechanisms. In systemic autoimmune diseases, in which various target organs are involved (nonorgan-specific), the peripheral blood NK level is generally lower than normal. This most likely allows the expression of autoimmune phenomena such as B cell hyperactivity and polyclonal antibody production, as is seen in SLE, due to a defect in the termination of the immune response. In autoimmune diseases with more localized, organ-specific lesions one can detect increased NK activity at the target organ itself. In these instances, the cytotoxic characteristic of the NK cell is more prominent. This theory explains why both increased and decreased NK activity may be observed in autoimmune diseases. In some disorders in which decreased NK activity was suspected of being crucial, immunomodulators, known to increase NK activity, were administered. Yet it is still difficult to separate the NK activity from the effect of the remaining immune system.

Role of mevalonic acid in the regulation of natural killer cell cytotoxicity

Considerable evidence has accumulated for a role of a nonsteroidal mevalonate product in the regulation of DNA replication and cell division. We report here a similar requirement for mevalonate in a nonreplicative function, that of natural killer (NK) cell cytotoxicity. Treatment of NK cells with 10 microM compactin for 48 hr results in a significant inhibition of cytotoxicity which can be completely reversed by treatment with 1 mM mevalonate, but not cholesterol, dolichol, or isopentenyl adenine. Protein and RNA synthesis appear to be involved in this reversal. Treatment with compactin and reversal with mevalonate do not affect the phenotypic distribution of the effector cell population, and the cell type involved in the inhibition and reversal of cytotoxicity is a CD16 (Leu 11)-, Leu 19-positive, large granular lymphocyte. The conjugation of the target and effector cell early in the lytic pathway is inhibited by compactin treatment of the effector cell population, and this inhibition is reversed by mevalonate.

Biology of natural killer cells

Studies of cytotoxicity by human lymphocytes revealed not only that both allogeneic and syngeneic tumor cells were lysed in a non-MHC-restricted fashion, but also that lymphocytes from normal donors were often cytotoxic. Lymphocytes from any healthy donor, as well as peripheral blood and spleen lymphocytes from several experimental animals, in the absence of known or deliberate sensitization, were found to be spontaneously cytotoxic in vitro for some normal fresh cells, most cultured cell lines, immature hematopoietic cells, and tumor cells. This type of nonadaptive, non-MHC-restricted cellmediated cytotoxicity was defined as “natural” cytotoxicity, and the effector cells mediating natural cytotoxicity were functionally defined as natural killer (NK) cells. The existence of NK cells has prompted a reinterpretation of both the studies of specific cytotoxicity against spontaneous human tumors and the theory of immune surveillance, at least in its most restrictive interpretation. Unlike cytotoxic T cells, NK cells cannot be demonstrated to have clonally distributed specificity, restriction for MHC products at the target cell surface, or immunological memory. NK cells cannot yet be formally assigned to a single lineage based on the definitive identification of a stem cell, a distinct anatomical location of maturation, or unique genotypic rearrangements.

Possible regulation of autologous mixed lymphocyte reaction by OKM1+ NK cells

T cells are stimulated by autologous non-T cells and interleukin 2 (IL-2) is produced in the conventional autologous mixed lymphocyte reaction (AMLR) in young healthy controls. The role of cells with natural killer (NK) cell markers (OKM1+ cells or Leu 7+ cells) in the AMLR was studied. There were significant inverse correlations between the percentage of input OKM1+ cells minus monocyte (OKM1+ NK cells) and either AMLR proliferation (gamma = -0.9, P less than 0.001) or IL-2 production (gamma = -0.75, P less than 0.01) in the AMLR cultures after 7 days measured at 7 days. A statistically significant correlation was observed between the percentage of input Leu 7+ cells and AMLR proliferation (gamma = -0.64, P less than 0.05), but not IL-2 production. These results suggest that the AMLR is controlled by OKM1+ NK, perhaps acting through IL-2 regulation.

Modulation of human natural killer cell function by cytokines and rheumatic disease

The activity of natural killer (NK) cells can be modified by a number of factors that either increase or suppress cytotoxicity. We have investigated in detail the cytokine induced killing of a NK resistant renal carcinoma cell line Cur by human NK cells. Preincubation of peripheral blood mononuclear cells with interferon alpha (IFN alpha), interleukin 2 (Il-2), interleukin 1 (Il-1) and tumor necrosis factor alpha greatly increased the rate and magnitude of Cur killing. Positively selected CD16 (+) cells were found to respond to cytokine stimulation and to mediate Cur killing. The effects of Il-2 and IFNa could be upregulated by costimulation of effector cells with Il-1 or TNF alpha. It was shown that TNF alpha induced Il-2 receptor expression on CD16(+) cells alone and even more in combination with Il-2. Studies of NK cell function in various rheumatic diseases revealed reduced NK cytotoxicity in peripheral blood and synovial fluid (SF), both in rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA). By contrast, normal NK function was found in patients with ankylosing spondylitis (AS) and psoriatic arthritis. A discordance with regard to the percentage of Leu 7 positive mononuclear cells and NK function in peripheral blood and SF was demonstrated. Minimal expression of Leu 7 positive cells and cytotoxicity was present in synovial membranes. NK function in rheumatic disease was largely independent of drug therapy. Natural killer (NK) cells are a subset of lymphocytes that mediate spontaneous cytotoxicity against certain tumor and virus infected cells without any known prior sensitation.(ABSTRACT TRUNCATED AT 250 WORDS)

Natural cell-mediated cytotoxicity in vitiligo

Natural cell-mediated cytotoxicity was studied in 18 patients with vitiligo and 13 healthy age-, race-, and sex-matched control subjects. The 4-hour chromium51 (51Cr) release assay was used to determine the activity of natural killer (NK) cells in the peripheral blood against K562 and Molt-4 target cells. Patients with vitiligo had a 50%, 67%, and 60% decrease in the cytotoxic response with Molt-4 cells at effector-target ratios of 25:1, 50:1, and 100:1, respectively, in comparison with control subjects (p less than 0.001). This inhibition was consistent with an 80% decrease in the binding capacity of NK cells to Molt-4 target cells (p less than 0.005). In contrast, cytotoxic responses did not differ in patients and control subjects with K562 target cells. These results suggest that patients with vitiligo have a decreased capacity for effector cell recognition of Molt-4 target cells but not K562 target cells. Hence patients with vitiligo may have defective clones of NK cells that are incapable of initial recognition of Molt-4 target cells, a necessary prerequisite for target cell lysis. Perhaps this phenomenon occurs with other tumor cells, which would explain the association of vitiligo with certain internal malignancies.