Cytotoxic antibodies to natural killer cells in systemic lupus erythematosus

Autoantibodies to killer cell immunoglobulin-like receptor 3DL1 in patients with systemic lupus erythematosus

A genetic variant of the killer immunoglobulin-like receptor 3DL1 (KIR3DL1) has been found in patients with systemic lupus erythematosus (SLE). Herein, we investigated the presence of autoantibodies to KIR3DL1 in a cohort of patients with SLE. We tested sera from 28 patients with SLE, 11 patients with rheumatoid arthritis (RA) and 17 healthy control subjects for anti-KIR3DL1 activity by an enzyme-linked immunosorbent assay (ELISA) using recombinant KIR3DL1-enhanced green fluorescent protein (EGFP) and EGFP proteins. Anti-KIR3DL1 antibodies were detected in 22 (79%) of the 28 patients with SLE, whereas they were present in only three (27%) of the 11 patients with RA examined. Notably, 10 (91%) of the 11 samples from patients with SLE prior to therapy had anti-KIR3DL1 antibodies. None of the samples from healthy donors were positive for the antibodies. Here, we report the presence of anti-KIR3DL1 antibodies in the sera of patients with SLE for the first time. Anti-KIR3DL1 autoantibodies may be involved in the pathogenesis of autoimmune diseases.

Functional anti-CD94/NKG2A and anti-CD94/NKG2C autoantibodies in patients with systemic lupus erythematosus

OBJECTIVE

Recently we serendipitously identified a patient with systemic lupus erythematosus (SLE) who was positive for autoantibodies to CD94/natural killer receptor group 2A (NKG2A). The present study was undertaken to investigate the occurrence and function of autoantibodies targeting lectin-like NK cell receptors in SLE.

METHODS

Sera from 203 SLE patients and 90 healthy individuals were analyzed, by flow cytometry, for Ig binding to Ba/F3 cells transfected with CD94/NKG2A, CD94/NKG2C, or NKG2D. Autoantibodies identified were characterized with regard to interference with HLA-E binding, effect on NK cell activation in response to HLA-E-transfected K562 cells, and capacity to facilitate antibody-dependent cell-mediated cytotoxicity (ADCC). Levels of autoantibodies were determined in longitudinally sampled sera, and correlations with disease activity (SLE Disease Activity Index 2000) and severity (Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index) were investigated.

RESULTS

Anti-CD94/NKG2A autoantibodies were identified in 7 SLE patients. The autoantibodies from 6 patients inhibited binding of HLA-E to CD94/NKG2A, whereas those from the seventh patient augmented this binding. Autoantibodies from 2 patients also reacted with the activating receptor CD94/NKG2C, with inhibition of the binding of HLA-E to CD94/NKG2C observed in 1 case and enhancement of this binding in the other. None of the sera contained anti-NKG2D autoantibodies. The levels of anti-CD94/NKG2A and anti-CD94/NKG2C autoantibodies correlated with disease activity and with a more severe SLE phenotype. Mechanistically, anti-CD94/NKG2A and anti-CD94/NKG2C autoantibodies both interfered with HLA-E-mediated regulation of NK cell activation and facilitated the elimination of target cells expressing CD94/NKG2A or CD94/NKG2C through ADCC.

CONCLUSION

Anti-CD94/NKG2A and anti-CD94/NKG2C autoantibodies occur in a subset of patients with clinically active SLE. Given their capacity to deplete certain NK cell subsets and interfere with particular NK cell function, such autoantibodies may promote the pathogenesis of SLE.

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.

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.

Isotype, distribution and target analysis of lymphocyte reactive antibodies in patients with human immunodeficiency virus infection

Anti-lymphocyte (ALA) antibodies were investigated by using both microcytotoxicity and immunofluorescence analyses in 87 subjects with different clinical features of human immunodeficiency virus (HIV) infection. A similar mean percentage of killing in microcytotoxicity assays using heterologous lymphocytes as cellular target was recorded in four groups of patients, including 36 HIV-seropositive asymptomatic subjects, 34 patients with HIV-induced lymphadenopathy syndrome (LAS), 13 with acquired immunodeficiency syndrome (AIDS)-related complex (ARC), and 4 patients with the full-blown AIDS. Conversely, an increasing percentage of ALA-positive subjects paralleled the evolution of the HIV infection. The majority of ALA were IgM isotype with a significant reactivity against T cells. This specificity was indifferently directed to CD3+, CD4+, and CD8+ lymphocytes. In additional experiments employing enzymatic digestion of lymphocyte membrane antigens, we demonstrated that CD4 and CD8 receptors were digested by the pronase, whereas CD3 molecules were highly resistant. Subsequent flow cytometry analyses using these pronase-digested T cells showed that reactivity of ALA for their target was unchanged. Our data suggest that antigenic specificities of ALA in HIV infection are resistant to pronase treatment and are not related to CD4 and CD8 molecules.

Family study of natural killer cell activity in C1q-deficient patients with systemic lupus erythematosus-like syndrome: association between impaired natural killer cell function and C1q deficiency

Impaired natural killer (NK) cell activity has been found in patients with systemic lupus erythematosus (SLE)-like syndrome. The mechanism by which NK cell function is impaired in SLE patients is not quite clear. We report here a family study of NK cell activity in C1q-deficient patients with SLE-like syndrome. In both SLE-active and SLE-inactive stages of the disease, NK cell function was significantly impaired when compared with the healthy controls (10.6 +/- 2.3% and 16.9 +/- 4.8% to 34.7 +/- 9.6%, p less than 0.025). On the other hand, differences in NK cell cytotoxicity between SLE-active and SLE-inactive members of the family were not statistically relevant (p less than 0.1). Further, we found no correlation between NK cell activity and clinical or laboratory values, except for a positive correlation between function of NK cells and C1q and CH50 values, respectively (rs = 0.93, 0.01 less than p less than 0.02). To our knowledge, this is the first report on a notable association between impaired NK cell activity and C1q deficiency. The type of inheritance of C1q deficiency in this family is also discussed.

Isotype and cytotoxicity spectra of anti-lymphocyte antibodies in patients with systemic lupus erythematosus

IgG anti-lymphocyte antibodies (ALA) reactive with resting lymphocytes were demonstrated in sera of patients with systemic lupus erythematosus (SLE) by immunofluorescence and flow cytometry and were shown (i) to bind T cells by non-Fc receptor-related mechanisms, (ii) to potentiate antibody-dependent cellular cytotoxicity (ADCC) of lymphocytes in vitro which correlated with binding to T cells, and (iii) to occur at a similar frequency in 29 SLE sera (56%) as IgM ALA (59%). IgG ALA levels in sera negatively correlated with absolute numbers of circulating lymphocytes in patients (r = -0.48, P less than 0.05), as did IgM ALA levels (r = -0.54, P less than 0.05); however, a stronger correlation resulted when levels of both ALA isotypes were considered together (r = -0.61, P less than 0.01). Different groups of SLE patients were distinguished with respect to relative serum content of IgM and IgG ALA and corresponding serum capacity to predominantly mediate ADCC, complement-dependent cytotoxicity (CDC), or both. No correlation existed between serum ADCC and CDC activities in vitro (r = 0.22). However, SLE patient lymphocyte counts negatively correlated with ADCC (r = -0.59, P less than 0.01) and to a lesser but still significant extent with CDC (r = -0.47, P less than 0.05). The latter results suggested that ADCC, induced by serum IgG ALA, was a mechanism of cytoloysis which occurred independently of CDC and which, like CDC, was significantly associated with lymphopenia in vivo.

Interleukin-2 restores the depressed allogeneic cell-mediated lympholysis and natural killer cell activity in patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by a variety of profound T-cell abnormalities among which are decreased cytotoxic capacity measured by allogeneic cell-mediated lympholysis (CML), natural killer cell (NK) activity, and decreased lymphokine production. In a group of 13 patients with active SLE, allogeneic CML, tested by a 4-hr 51Cr-release assay, was 18.2 +/- 2.7% while in the group of normal individuals CML was 41.2 +/- 2.7%. If optimal doses of affinity-purified interleukin-2 (IL-2) were present during the mixed lymphocyte culture, the CML of SLE patients was increased to normal levels (40.4 +/- 4.0%). In contrast, interferon-alpha (IFN-alpha) increased (but not significantly) the levels of CML. Mixed lymphocyte reaction, tested by tritiated thymidine incorporation, was also decreased in the group of patients (14,820 +/- 815 cpm vs 28,972 +/- 5880 cpm in normals) and it was increased to normal levels if IL-2, but not IFN-alpha was added to the cultures. NK activity was decreased in the group of patients tested by 51Cr-release assay, harvested at 6 and 18 hr. IL-2 increased the NK activity up to normal levels, while IFN-alpha was only partially efficacious. These results demonstrate that IL-2, but not IFN-alpha, can potentiate or even fully restore the deficient cytotoxic effector function of peripheral mononuclear cells in patients with SLE.

Inhibition of natural killer cell activity by serum from patients with systemic lupus erythematosus: roles of disease activity and serum interferon

Among their immunological alterations patients with systemic lupus erythematosus (SLE) have been shown to have diminished natural killer (NK) cell activity. This abnormality is at least in part related to humoral factors, as sera from patients with SLE can inhibit the NK activity of peripheral blood mononuclear cells from normal individuals. The present study extends these findings to demonstrate that the inhibitory ability of sera from patients with SLE varies with disease activity. Furthermore, sera from patients with active SLE containing interferon (IFN), a potent stimulator of NK activity, were equally or more inhibitory than sera which did not contain IFN. Thus the factors in SLE sera which can inhibit NK function vary with disease activity and cannot be overcome by IFN present in these sera.

Decreased natural killer cell activity in generalized pustular psoriasis (von Zumbusch type)

Mononuclear cells isolated from the peripheral blood of four untreated patients with pustular psoriasis (von Zumbusch type) displayed greatly diminished natural killer cell activity against K-562 erythroleukaemic target cells in a 51Cr release assay when compared with mononuclear cells from healthy controls.

Phenotypes of T lymphocytes in systemic lupus erythematosus: decreased cytotoxic/suppressor subpopulation is associated with deficient allogeneic cytotoxic responses rather than with concanavalin A-induced suppressor cells

Patients with systemic lupus erythematosus (SLE) have decreased precursors of cytotoxic/suppressor T lymphocytes in their peripheral blood, as determined by monoclonal antibodies. To determine whether decrease of the cytotoxic or the suppressor parts (or both) of this subpopulation of T lymphocytes is being reflected by this peripheral mononuclear cell (MNC) abnormality, a series of experiments was conducted in which both the suppressive function (concanavalin A induced and spontaneous) and the generation of cytotoxic responses against alloantigens were tested. Cytotoxic responses were consistently diminished while suppressor capacity of MNC from patients with SLE (measured on several assays of normal T- and B-lymphocyte functions) was comparable to that of MNC from normal individuals. The defect in cytotoxic responses to alloantigens by MNC from SLE patients persisted following secondary stimulation in mixed-leukocyte cultures; the cytotoxic responses were not amplified and remained well below the responses of normal MNC. These experiments indicate that the decreased peripheral population of cytotoxic/suppressor lymphocytes in SLE patients represents low or absent precursors of cytotoxic cells rather than of precursors of suppressor cells.