Characteristics and clustering analysis of peripheral blood lymphocyte subsets in children with systemic lupus erythematosus complicated with clinical infection

OBJECTIVES

Clinical infection is a common complication in children with systemic lupus erythematosus (SLE). However, few studies have investigated immune alterations in children with SLE complicated with clinical infection. We assessed lymphocyte subsets in children with SLE to explore the possibility of clinical infection.

METHODS

We retrospectively analyzed the proportion of peripheral lymphocyte subsets in 140 children with SLE. Children with SLE were classified into different clusters according to the proportion of peripheral blood lymphocyte subsets: (CD3 + /CD4 + T cell, CD3 + /CD8 + T cell, CD3 + /CD4 + /CD8 + T cell, CD3 + /CD4-/CD8- T cell, CD19 + B cell, and CD3-/CD16 + /CD56 + NK cell). Differences in the proportion of lymphoid subsets, infection rates, and systemic lupus erythematosus disease activity index (SLEDAI) scores were compared between clusters. In addition, we grouped the subjects according to the presence or absence of infection. Proportions of lymphoid subsets, demographic variables, clinical presentation, and other laboratory variables were compared between the infected and uninfected groups. Finally, the diagnostic ability of lymphocyte subset ratios to distinguish secondary infection in children with SLE was predicted using an ROC curve.

RESULTS

Cluster C2 had a higher proportion of B cells than Cluster C1, while Cluster C1 had a lower proportion of NK cells, CD3 + T cells, CD3 + /CD4 + T cells, CD3 + /CD8 + T cells, and CD3 + /CD4-/CD8- T cells. Infection rates and SLEDAI scores were higher in Cluster C2 than in Cluster C1. The infected children had a higher proportion of B cells and a lower proportion of CD3 + T cells, CD3 + /CD4 + T cells, CD3 + /CD8 + T cells, and CD3 + /CD4-/CD8- T cells. There were no significant differences in lymphoid subsets between children in Cluster C2 and the infected groups. The area under the ROC curve of B lymphocytes in predicting SLE children with infection was 0.842. The area under the ROC curve was 0.855 when a combination of B cells, NK cells, CD4 + T cells, and CD8 + T cells was used to predict the outcome of coinfection.

CONCLUSIONS

A high percentage of B cells and a low percentage of CD3 + T cells, CD3 + /CD4 + T cells, CD3 + /CD8 + T cells, CD3 + /CD4 + /CD8 + T cells, and CD3 + /CD4-/CD8- T cells may be associated with infection in children with SLE. B cells was used to predict the outcome of coinfection in children with SLE. Key Points • A high percentage of B cells and a low percentage of CD3 + T cells, CD3 + /CD4 + T cells, CD3 + /CD8 + T cells, CD3 + /CD4 + /CD8 + T cells, and CD3 + /CD4-/CD8- T cells may be associated with infection in children with SLE • B cells was used to predict the outcome of coinfection in children with SLE.

Genetic Dissection of Sle Pathogenesis: Sle3 on Murine Chromosome 7 Impacts T Cell Activation, Differentiation, and Cell Death

Polyclonal, generalized T cell defects, as well as Ag-specific Th clones, are likely to contribute to pathology in murine lupus, but the genetic bases for these mechanisms remain unknown. Mapping studies indicate that loci on chromosomes 1 (Sle1), 4 (Sle2), 7 (Sle3), and 17 (Sle4) confer disease susceptibility in the NZM2410 lupus strain. B6.NZMc7 mice are C57BL/6 (B6) mice congenic for the NZM2410-derived chromosome 7 susceptibility interval, bearing Sle3. Compared with B6 controls, B6.NZMc7 mice exhibit elevated CD4:CD8 ratios (2.0 vs 1.34 in 1- to 3-mo-old spleens); an age-dependent accumulation of activated CD4+ T cells (33.4% vs 21.9% in 9- to 12-mo-old spleens); a more diffuse splenic architecture; and a stronger immune response to T-dependent, but not T-independent, Ags. In vitro, Sle3-bearing T cells show stronger proliferation, increased expansion of CD4+ T cells, and reduced apoptosis (with or without anti-Fas) following stimulation with anti-CD3. With age, the B cells in this strain acquire an activated phenotype. Thus, the NZM2410 allele of Sle3 appears to impact generalized T cell activation, and this may be causally related to the low grade, polyclonal serum autoantibodies seen in this strain. Epistatic interactions with other loci may be required to transform this relatively benign phenotype into overt autoimmunity, as seen in the NZM2410 strain.

Cellular Immunity to β2-Glycoprotein-1 in Patients with the Antiphospholipid Syndrome

Patients with antiphospholipid syndrome (APS) suffer recurrent thromboses, thrombocytopenia, and/or fetal loss in association with Abs that can be detected in phospholipid-dependent assays. Despite the name, the Igs associated with APS are predominantly directed against epitopes on phospholipid-binding plasma proteins, such as β2-glycoprotein-1 (β2GP1) and prothrombin. The aim of this study was to examine the cellular immune response to β2GP1 in patients with APS. Using a serum-free stimulation assay, PBMCs from 8 of 18 patients with APS proliferated to purified β2GP1 or to the β2GP1 present in serum, whereas no stimulation was observed by PBMCs from healthy individuals, patients with other autoimmune diseases, or anticardiolipin Ab-positive patients without histories of thromboses or fetal loss. The immune response was Ag-specific, requiring class II molecules, CD4+ T cells, and APCs, and was associated with a selective expansion of CD4+ but not CD8+ T cells. The proliferating T cells produced IFN-γ but not IL-4, indicating a bias toward a type 1 immune response. Chronic low grade stimulation of autoreactive β2GP1-specific, IFN-γ-producing Th1 CD4+ T cells may contribute to the high risk of thromboses and pregnancy failure in patients with APS.

Defective Self-Reactive Antibody Repertoire of Serum IgM in Patients with Hyper-IgM Syndrome

We have analyzed the self-reactive repertoires of IgM and IgG Abs in the serum of 19 patients with hyper-IgM syndrome (HIM) by means of a quantitative immunoblotting technique that allows for a quantitative comparison of Ab repertoires in health and disease by multiparametric statistical analysis. Normal tissue extracts of liver, lung, stomach, and kidney were used as sources of self Ags. Extracts of Pseudomonas aeruginosa and Staphylococcus epidermidis were used as sources of nonself Ags. We demonstrate a significant bias in repertoires of reactivities of IgM of patients with HIM with self Ags. Ab repertoires of IgM toward nonself Ags did not differ, however, between patients and controls. No difference was found between IgM repertoires of untreated patients and those of patients receiving substitutive treatment with i.v. IgG. IgG in the serum of HIM patients lacked reactivity with self Ags, although it exhibited a pattern of reactivity with nonself Ags that was similar to that of IgG of healthy controls. The data demonstrate that functional CD40-CD40 ligand interactions are essential for the selection of natural self-reactive B cell repertoires.

Genetic Dissection of SLE Pathogenesis: Adoptive Transfer of Sle1 Mediates the Loss of Tolerance by Bone Marrow-Derived B Cells

Sle1 is a potent autoimmune susceptibility locus on chromosome 1 originally identified in a genome scan of testcross progeny between the systemic lupus erythematosus-prone NZM2410 strain and C57BL/6. We subsequently produced B6.NZMc1, a congenic strain carrying the NZM2410-derived Sle1 genomic interval on the B6 background and demonstrated that Sle1 mediated the loss of tolerance to chromatin in both the B and T cell compartments. In this communication, we show by adoptive transfer experiments that the autoimmune phenotypes of Sle1 are completely reconstituted in B6 radiation chimeras receiving B6.NZMc1 bone marrow but not by the reciprocal reconstitution, demonstrating that Sle1 is functionally expressed in B cells. In additional experiments, cotransfer of mixtures of bone marrow derived from B6.NZMc1 and nonautoimmune congenic B6 mice carrying allelic T and B cell markers showed that only B cells derived from B6.NZMc1 bone marrow produced anti-chromatin autoantibodies. In contrast, increased expression of CD69 was equivalent in CD4+ T cells derived from either B6.NZMc1 or congenic B6 bone marrow, suggesting that either T cell population could be activated subsequent to loss of tolerance in the B cell compartment. These findings indicate that the expression of Sle1 in B cells is essential for the development of autoimmunity.

Thymic Expression of the Transcription Factor Nur77 Rescues the T Cell But Not the B Cell Abnormality of gld/gld Mice

Fas and Fas ligand are critical regulators of lymphocyte homeostasis. Disruption of this pathway in the spontaneous mouse mutant gld leads to autoimmunity characterized by the appearance of a population of CD4−8−B220+ T cells and the production of autoantibodies. Nur77 is a transcription factor that is induced upon TCR signaling. Constitutive thymic expression of Nur77 leads to apoptosis. We have previously shown that introduction of this Nur77 transgene can eliminate the accumulation of abnormal T cells in the periphery of gld/gld mice. In this report, we further characterized the effects of the Nur77 transgene on the gld phenotype. Nur77-mediated apoptosis is evident in the thymuses of mice with either a gld/gld homozygous or gld/+ heterozygous background. Consequently, few mature T cells are generated in these mice. In addition, mature T cells exhibit a diminished response to proliferative signals through CD3. Interestingly, the Nur77 transgene failed to reduce serum levels of Igs and anti-DNA Abs to wild-type levels. These data suggest that the rescue of the T cell lymphoproliferative syndrome in gld/gld mice by the Nur77 transgene is mediated by events in the thymus and that B cell autoimmune disease associated with the gld mutation can develop independently of the T cell abnormality.

Resistance to HgCl2-Induced Autoimmunity in Haplotype-Heterozygous Mice Is an Intrinsic Property of B Cells

Exposure to low doses of mercury chloride induces autoantibodies to the nucleolar protein fibrillarin in H-2s, but not in H-2b, mice. Surprisingly, F1 crosses between resistant and sensitive haplotypes are resistant. Previously, we have shown that the resistance in these F1 mice was due to coexpression of the resistant class II allele. Using adoptive transfer techniques we have examined several mechanisms by which the resistant haplotype could be down-regulating the antifibrillarin response in F1 (s/b) mice. Similar to other autoimmune models, mercury-induced autoimmunity requires cognate MHC-restricted T cell help. The absence of autoantibody production in F1 mice was not due to a difference in thymic education or to the absence of antifibrillarin-specific T cell help. These results suggest that the resistance is due to an intrinsic property of the haplotype-heterozygous B cells.

Novel Immunoregulatory B Cell Pathways Revealed by lpr-+ Mixed Chimeras

lpr, a murine mutation of the Fas apoptosis receptor, causes lymphadenopathy and autoantibody production, with lymphadenopathy primarily due to a population of CD4−CD8−B220+ T cells. Previous in vivo experiments, in which lpr and normal bone marrow cells were coinfused into lpr hosts, have demonstrated that only T cells of lpr origin accumulated abnormally and only B cells of lpr origin produced autoantibodies. Moreover, in these chimeras, B cells of normal origin were unable to respond to conventional, T cell-dependent exogenous Ag. To address the role of lpr B cells in regulation of lpr autoimmunity, we have prepared lpr-+ mixed chimeras and selectively eliminated lpr B cells using allele-specific, mAb treatment, thus allowing normal B cells to develop in an environment with lpr T cells. From these data, we arrived at four major conclusions: 1) Compared with control-treated chimeric mice, lpr B cell-depleted mice had greatly reduced total lymph node cell counts; 2) the T cells were derived equally from normal and lpr donors, and the percentage of lpr-derived CD4−CD8− T cells was greatly reduced; 3) despite the presence of the remaining lpr T cells, no autoantibodies were produced by the normal derived B cells; and 4) lpr T cells without lpr B cells were unable to prevent a normal B cell response to conventional Ag. These data demonstrate that B cells can play a critical and expansive regulatory role, not only for T cells, but for other B cells as well.