Enforced and prolonged CD40 ligand expression triggers autoantibody production in vivo

Hydroxychloroquine inhibits CD154 expression in CD4+ T lymphocytes of systemic lupus erythematosus through NFAT, but not STAT5, signaling

Background

Overexpression of membranous CD154 in T lymphocytes has been found previously in systemic lupus erythematosus (SLE). Because hydroxychloroquine (HCQ) has been used frequently in the treatment of lupus, we sought to identify the effects of HCQ on CD154 and a possibly regulatory mechanism.

Methods

CD4⁺ T cells were isolated from the blood of lupus patients. After stimulation with ionomycin or IL-15 and various concentrations of HCQ, expression of membranous CD154 and NFAT and STAT5 signaling were assessed.

Results

HCQ treatment had significant dose-dependent suppressive effects on membranous CD154 expression in ionomycin-activated T cells from lupus patients. Furthermore, HCQ inhibited intracellular sustained calcium storage release, and attenuated the nuclear translocation of NFATc2 and the expression of NFATc1. However, CD154 expressed through IL-15-mediated STAT5 signaling was not inhibited by HCQ treatment.

Conclusions

HCQ inhibited NFAT signaling in activated T cells and blocked the expression of membranous CD154, but not STAT5 signaling. These findings provide a mechanistic insight into SLE in HCQ treatment.

Post-transcriptional regulation in lymphocytes: the case of CD154

The control of mRNA decay is emerging as an important control point and a major contributor to gene expression in both immune and non-immune cells. The identification of protein factors and cis-acting elements responsible for transcript degradation has illuminated a comprehensive picture of precisely orchestrated events required to both regulate and establish the decay process. One gene that is highly regulated at the post-transcriptional level is CD40 ligand (CD154 or CD40L). CD154 on CD4(+) T cells is tightly controlled by an interacting network of transcriptional and post-transcriptional processes that result in precise surface levels of protein throughout an extended time course of antigen stimulation. The activation-induced stabilization of the CD154 transcript by a polypyrimidine tract-binding protein (PTB)-complex is a key event that corresponds to the temporal expression of CD154. In this review, we discuss known and potential roles of major mRNA decay pathways in lymphocytes and focus on the unique post-transcriptional mechanisms leading to CD154 expression by activated CD4(+) T cells.

Estrogen does not regulate CD154 mRNA stability in systemic lupus erythematosus T cells

Previous studies in our laboratory showed a dose-dependent and hormone-specific increase in CD154 expression in T cells from females with systemic lupus erythematosus (SLE). This present study investigates if the estrogen-dependent increase in CD154 expression is due to stabilization of the messenger RNA. T cells from female SLE patients and controls were cultured for 18 h in serum-free medium without and with estradiol 17-beta (10(-7) M). T cells were either unstimulated (resting) or were activated by further culture on anti-CD3 coated plates. Actinomycin D (25 microg/mL) was added to parallel cultures to inhibit new messenger RNA synthesis. CD154 messenger RNA stability was assessed by reverse-transcription polymerase chain amplification. Resting SLE (n = 10, P = 0.88) and normal (n = 7, P = 0.65) T cells showed no significant differences in message stability in response to estradiol. CD154 messenger RNA was also not significantly stabilized in activated SLE (n = 10, P = 0.15) or activated normal (n = 6, P = 0.077) T cells in response to estradiol. These findings indicate that the estrogen-dependent increase in CD154 in SLE T cells is not due to stability of the mRNA. These data are consistent with the postulate that estradiol stimulates CD154 transcription in SLE T cells.

Elevated levels of soluble CD40 ligand (sCD40L) in serum of patients with systemic autoimmune diseases

The CD40-CD40L costimulatory pathway is involved in the evolution of many autoimmune diseases including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and Sjögren's syndrome (SS). Increased levels of sCD40L in the serum have been associated with disease activity in SLE. The aim of this study was to investigate the role of sCD40L in the development of lupus nephritis and examine its possible association with cryoglobulinemia in Sjögren's syndrome. We used a 2-site sandwich ELISA to measure the levels of sCD40L in sera, from 64 patients with SLE, RA and SS and 17 healthy blood donors. Biological specimens from the affected tissues such as urine from patients with lupus nephritis and saliva from patients with SS were also tested. In this regard, paired sera and first morning urine samples from 6 SLE patients (3 with active lupus nephritis and 3 with inactive lupus nephritis) were tested with the sCD40L ELISA protocol as well as paired sera and salivary samples from 5 patients with SS and cryoglobulinemia, 5 patients with SS and anti-Ro or anti-La autoantibodies and 5 age-matched healthy control donors. We also examined possible correlations of sCD40L levels with several laboratory and clinical parameters in SS and SLE. We found that sera from SLE and SS patients had significantly higher levels of sCD40L compared to sera from healthy control donors. No sCD40L was detected, in urine samples of patients with either active or inactive nephritis and in salivary samples from SS patients or normal subjects. Soluble CD40L is elevated in sera of SS and SLE patients but further investigation is needed to determine its possible role in SLE nephritis and Sjögren's syndrome.

Differential responses of human B-lymphocyte subpopulations to graded levels of CD40-CD154 interaction

Naïve and memory B-lymphocyte populations are activated by CD154 interaction through cell-surface CD40. This interaction plays an important role in the regulation of the humoral immune response, and increasing evidence indicates that fine variation in CD40 binding influences B lymphocytes, macrophages and dendritic cells in murine models. Here we have investigated whether and how variations in the intensity of the CD40-CD154 interaction could contribute to differential regulation of human B-lymphocyte populations. Proliferation and differentiation of B lymphocytes were monitored in response to graded levels of CD40 stimulation in the presence of interleukin (IL)-2, IL-4 and IL-10. Our results show that the level of CD154 binding to CD40 on B lymphocytes can directly influence the evolution of CD19(+) CD27(-) and CD19(+) CD27(+) cell populations. Furthermore, proliferation, global expansion of CD19(+) cells and emergence of CD38(++) CD138(+) cells, as well as immunoglobulin G (IgG) and IgM secretion, were affected by the level of exposure of B lymphocytes to CD154. These results suggest that the CD40-CD154 interaction is more like a rheostat than an on/off switch, and its variation of intensity may play a role in the regulation of B-lymphocyte activation following the primary and/or secondary humoral immune response.

B cell receptor (BCR) cross-talk: CD40 engagement enhances BCR-induced ERK activation

Bystander B cells may be initially stimulated through CD40, which enhances susceptibility to Fas-mediated apoptosis, before encountering Ag, which produces Fas resistance. A key issue in this process is to what extent CD40 cross-talk might affect subsequent BCR signaling. It has previously been shown that CD40 engagement bypasses or mitigates the need for Bruton's tyrosine kinase in subsequent BCR signaling for NF-kappaB activation. However, the full extent of the effects of CD40 on BCR signaling has not been delineated. In the present study we evaluated the possibility that CD40-mediated cross-talk also affects another principal outcome of BCR signaling: MAPK activation. We found that prior stimulation of primary murine B cells with CD40L markedly enhanced the level of ERK and JNK (but not p38 MAPK) phosphorylation produced by subsequently added anti-Ig Ab, and much, but not all, of this enhancement was independent of PI3K and phospholipase C. CD40L treatment similarly enhanced BCR-induced MAPK kinase (MEK) phosphorylation, and MEK was required for enhancement of ERK. Although BCR-induced c-Raf phosphorylation was also enhanced by prior CD40L treatment, c-Raf was not required for MEK/ERK phosphorylation. These results identify a novel system of receptor cross-talk between CD40 and BCR and indicate that the effects of CD40 engagement on subsequent BCR stimulation spread beyond NF-kappaB to involve the MAPK pathway.

CD40: a growing cytoplasmic tale

CD40, a member of the tumor necrosis factor (TNF) receptor family that is expressed on B cells, monocytes, dendritic cells, endothelial cells, and epithelial cells, as well as on B cell lymphomas and carcinomas, activates multiple signaling pathways. In B cells, the response to CD40 is complex and depends on the maturation status of the cell. It is well established that CD40 can promote cell survival through up-regulation of the expression of genes encoding antiapoptotic proteins. However, a new role for CD40 signaling is being recognized in promoting progression through the cell cycle. The roles of the phosphoinositide 3-kinase, mitogen-activated protein kinase, and nuclear factor kappaB pathways in mediating CD40 stimulation of the cell cycle are described.

CD154 transcriptional regulation in primary human CD4 T cells

CD154 (CD40-ligand) has a wide variety of pleiotropic effects throughout the immune system and is critical to both cellular and humoral immunity. Cell surface and soluble CD154 are primarily expressed by activated CD4 T cells. Expression of CD154 is tightly regulated in a time-dependent manner, and, like most T cell-derived cytokines and other members of the tumor necrosis factor (TNF) superfamily, CD154 is largely regulated at the level of gene transcription. Recently, dysregulated expression of CD154 has been noted in a number of autoimmune disorders, including systemic lupus erythematosus (SLE). In addition, abnormal expression of CD154 has been hypothesized to contribute to a wider array of diseases, from atherosclerosis to Alzheimer's disease. Until recently, very little was known about the transcriptional regulation of CD154. We are exploring CD154 regulation in primary human CD4 T cells in hopes of understanding the cis- and trans-regulatory elements that control its expression in the cells that normally express CD154. Ultimately, we hope to be able to correct abnormal expression of CD154 in various disease states and to help design gene therapy vectors for treating CD154-deficient individuals with hyper-IgM syndrome.

The dinucleotide repeat polymorphism in the 3'UTR of the CD154 gene has a functional role on protein expression and is associated with systemic lupus erythematosus

OBJECTIVE

To investigate the association of the (CA)n dinucleotide repeat in the 3' untranslated region (3'UTR) of the CD154 gene with systemic lupus erythematosus (SLE), and its functional role in protein expression.

METHODS

The allelic and genotypic distributions of the polymorphism were compared in 80 patients with SLE and 80 controls. A complete clinical and analytical database was recorded in each patient in order to correlate the clinical manifestations in SLE with different alleles. To investigate the functional role of the polymorphism, the CD154 protein expression on activated lymphocytes from healthy homozygous controls was evaluated by flow cytometry.

RESULTS

The 24 CA allele was the most represented in controls (p = 0.029), whereas the alleles containing >24 CA repeats were found in patients (p = 0.0043). Furthermore, when only homozygous women were considered, most controls carried two 24 CA alleles (p = 0.041), whereas most patients carried two alleles containing >24 CA repeats (p = 0.032). Also, patients carrying at least one 24 CA allele had less neurological involvement (p = 0.034), and carriers of at least one allele with fewer than 24 CA repeats presented more livedo reticularis (p = 0.006) and anti-Sm (p = 0.01) and anti-RNP (p = 0.038) autoantibodies. CD154 maximum expression in activated lymphocytes from all controls was reached after 54 hours, but it was more prolonged in controls carrying two alleles with >24 CA repeats (p = 0.0068).

CONCLUSION

The CD154 3'UTR microsatellite is associated with SLE, and the most represented alleles in patients were accompanied by a more prolonged protein expression in activated lymphocytes from controls.

Abnormal germinal center reactions in systemic lupus erythematosus demonstrated by blockade of CD154-CD40 interactions

To determine the role of CD154-CD40 interactions in the B cell overactivity exhibited by patients with active systemic lupus erythematosus (SLE), CD19+ peripheral B cells were examined before and after treatment with humanized anti-CD154 mAb (BG9588, 5c8). Before treatment, SLE patients manifested activated B cells that expressed CD154, CD69, CD38, CD5, and CD27. Cells expressing CD38, CD5, or CD27 disappeared from the periphery during treatment with anti-CD154 mAb, and cells expressing CD69 and CD154 disappeared from the periphery during the post-treatment period. Before treatment, active-SLE patients had circulating CD38 (bright) Ig-secreting cells that were not found in normal individuals. Disappearance of this plasma cell subset during treatment was associated with decreases in anti-double-stranded DNA (anti-dsDNA) Ab levels, proteinuria, and SLE disease activity index. Consistent with this finding, peripheral B cells cultured in vitro spontaneously proliferated and secreted Ig in a manner that was inhibited by anti-CD154 mAb. Finally, the CD38(+/++)IgD(+), CD38(+++), and CD38(+)IgD(-) B cell subsets present in the peripheral blood also disappeared following treatment with humanized anti-CD154. Together, these results indicate that patients with active lupus nephritis exhibit abnormalities in the peripheral B cell compartment that are consistent with intensive germinal center activity, are driven via CD154-CD40 interactions, and may reflect or contribute to the propensity of these patients to produce autoantibodies.

CD154 expression and mRNA stability of activated CD4-positive T cells in patients with systemic lupus erythematosus

Abstract The expression of CD154 (CD40 ligand) on activated CD4+ T cells is known to be transient and tightly regulated for antigen-specific immune responses, and is increased and prolonged among patients with systemic lupus erythematosus (SLE). We investigated the regulation of CD154 expression by determining the protein and mRNA expression with PMA and ionomycin stimulation in CD4+ T cells, and confirmed their increase and prolongation in SLE T cells. Treatment with actinomycin D, a transcription inhibitor, after PMA and ionomycin stimulation was performed, and the findings revealed that the stability of CD154 mRNA increased significantly in activated SLE T cells compared with that of controls. However, alternations or abnormal sequences were not identified in the 3″ untranslated region, including AU-rich elements and CU-rich sequences, while their partial involvement in the posttranscriptional regulation of CD154 mRNA stability has been reported. With 96 h culture in vitro, the destabilization of CD154 mRNA was demonstrated, resulting in a corresponding decrease and normalization of surface expression on activated SLE T cells. We speculate that the CD154 expression on T cells from SLE patients may be increased and prolonged, with mRNA stabilization being related to a continuous stimulation in vivo.

Improved immunogenicity of a self tumor antigen by covalent linkage to CD40 ligand

The interaction between the CD40 ligand (CD40L) and CD40 on antigen-presenting cells (APCs) is critical in promoting humoral and cellular immune responses. Agonistic anti-CD40 monoclonal antibody and soluble CD40L can act as powerful adjuvants to promote vaccination, but usually require repeated high-dose treatment. In this study, we demonstrate that the adjuvant effect of CD40L can be greatly improved by directly linking the antigen to CD40L. We constructed a fusion protein (Id-CD40L) consisting of the extracellular domain of CD40L and the idiotype (Id) protein, a weakly immunogenic tumor-specific antigen derived from the murine 38C13 B-cell lymphoma. The soluble Id-CD40L fusion protein retained CD40 binding activity and stimulated CD80 and CD86 upregulation and interleukin (IL)-12 production by macrophages. Immunization of mice with Id-CD40L without adjuvants resulted in high titers of anti-Id Abs dominated by the IgG1 isotype and protected the mice from subsequent lethal tumor challenge. In a dose-response study, we demonstrated that Id-CD40L elicited anti-Id antibody (Ab) responses in all immunized animals, even at a dose as low as 0.5 microg. Immunization with free Id and an IgG-CD40L fusion protein, which was identical in structure to Id-CD40L but lost the Id determinant, resulted in significant lower anti-Id responses, indicating that physical linkage between the tumor antigen and CD40L was required for the optimal immune response. These results demonstrate that fusing CD40L to a candidate antigen can greatly improve the adjuvant activity of CD40L. This approach may be useful in developing vaccines for a variety of malignant and infectious diseases.