Cytokine expression and regulation of human plasma cells: disappearance of interleukin-10 and persistence of transforming growth factor-beta 1

Plasma cells in immunopathology: concepts and therapeutic strategies

Plasma cells are terminally differentiated B cells that secrete antibodies, important for immune protection, but also contribute to any allergic and autoimmune disease. There is increasing evidence that plasma cell populations exhibit a considerable degree of heterogeneity with respect to their immunophenotype, migration behavior, lifetime, and susceptibility to immunosuppressive drugs. Pathogenic long-lived plasma cells are refractory to existing therapies. In contrast, short-lived plasma cells can be depleted by steroids and cytostatic drugs. Therefore, long-lived plasma cells are responsible for therapy-resistant autoantibodies and resemble a challenge for the therapy of antibody-mediated autoimmune diseases. Both lifetime and therapy resistance of plasma cells are supported by factors produced within their microenviromental niches. Current results suggest that plasma cell differentiation and survival factors such as IL-6 also signal via mammalian miRNAs within the plasma cell to modulate downstream transcription factors. Recent evidence also suggests that plasma cells and/or their immediate precursors (plasmablasts) can produce important cytokines and act as antigen-presenting cells, exhibiting so far underestimated roles in immune regulation and bone homeostasis. Here, we provide an overview on plasma cell biology and discuss exciting, experimental, and potential therapeutic approaches to eliminate pathogenic plasma cells.

IgA+ plasma cells in murine intestinal lamina propria as a positive regulator of Treg differentiation

Continuous exposure to commensal bacteria gives rise to a complex intestinal immune system that maintains local tolerance, which requires Foxp3-expressing Treg. Recently, the regulation of TFH function by plasma cells has been reported, but effects of intestinal LP-PCs, one of the richest plasma cells in the body, on T cell differentiation have not been studied. Here, we investigated whether IgA(+) LP-PCs from murine small intestines had effects on T cell differentiation. Surprisingly, when IgA(+) LP-PCs were cocultured with CD4(+) T cells, Foxp3 expression was increased significantly in CD4(+)CD25(-) T cells. Results using the Transwell coculture system revealed that soluble factors from LP-PCs, TGF-β, and RA were involved in the induction of Foxp3 expression. Furthermore, Foxp3(+)CD25(-) T cells were decreased in PP after intestinal depletion of plasma cells. In addition, intestinal colony transfer from SPF to germ-free mice was demonstrated to generate IgA(+) LP-PCs and Foxp3(+) T cells with meaningful correlation in LP. We report for the first time that IgA(+) LP-PCs induce Foxp3 expression in T cells through TGF-β and RA. LP-PCs generated by commensal bacteria may play a crucial role in intestinal immunity through the induction of Treg, as well as IgA production.

B-cell targeting agents in the treatment of multiple sclerosis

OPINION STATEMENT

The aims of this article are to discuss the potential role of B lymphocytes in the pathogenesis of multiple sclerosis (MS) and in the mechanisms of action of approved and emerging disease modifying therapies. Over the last few years, significant progress has been made in the introduction of novel pharmacologic treatments that reduce the frequency of clinical exacerbations and radiological lesion formation in relapsing remitting MS. The mechanisms of action of a number of these disease modifying therapies (DMT) implicate B cells in the pathogenesis, as well as in the regulation, of MS. Further research into B-cell subset trafficking patterns, functional activities and interactions with other immune cells in the context of neuroinflammation is likely to inform the development of future generations of DMT.

Matrix metalloproteinase-3 production by gut IgG plasma cells in chronic inflammatory bowel disease

BACKGROUND

In both ulcerative colitis (UC) and Crohn's disease (CD) there is a marked increase in mucosal IgG plasma cells (PC), although their precise role is not well established. In this study we isolated gut PCs from patients with IBD and normal controls and analyzed cytokine production, matrix metalloproteinase (MMP)-3 and tissue inhibitor of metalloproteinase (TIMP)-1 production, and PC longevity ex vivo.

METHODS

Lamina propria mononuclear cells (LPMCs) were isolated from patients with CD (n = 19), UC (n = 27), and normal controls (n = 42). PCs were further selected by immunomagnetic isolation using CD138 microbeads. Cytokine, MMP-3, and TIMP-1 expression was investigated by Taqman polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), Western blotting, and confocal microscopy. PC lifespan in vitro was studied by ELISpot analysis.

RESULTS

PCs from both controls and IBD patients contained high levels of transcripts for TGFbeta, whereas they did not contain significant transcripts for IL-4, IL-5, IL-10, IFNgamma, TNF, or IL-12p40. PCs from patients with CD and UC expressed significantly higher levels of MMP-3 protein and transcripts than controls (P < 0.0001). The vast majority of MMP-3-expressing PCs were IgG+ve. In culture, IgA PCs from both IBD patients and controls persisted for only a few days, but IgG PCs from IBD patients persisted for at least 3 weeks.

CONCLUSIONS

We have demonstrated that IgG PCs from patients with IBD express large amounts of MMP-3 and that they appear to be long-lived. These results identify a new pathway by which IgG PCs may damage the gut.

Junctional adhesion molecule C (JAM-C) distinguishes CD27+ germinal center B lymphocytes from non-germinal center cells and constitutes a new diagnostic tool for B-cell malignancies

Differentiation of naïve B cells into plasma cells or memory cells occurs in the germinal centers (GCs) of lymph follicles or alternatively via a GC- and T-cell-independent pathway. It is currently assumed that B-cell lymphomas correlate to normal B-cell differentiation stages, but the precise correlation of several B-cell lymphomas to these two pathways remains controversial. In the present report, we describe the junctional adhesion molecule C (JAM-C), currently identified at the cell-cell border of endothelial cells, as a new B-cell marker with a tightly regulated expression during B-cell differentiation. Expression of JAM-C in tonsils allows distinction between two CD27+ B-cell subpopulations: JAM-C- GC B cells and JAM-C+ non-germinal B cells. The expression of JAM-C in different B-cell lymphomas reveals a disease-specific pattern and allows a clear distinction between JAM-C- lymphoproliferative syndromes (chronic lymphocytic leukemia, mantle cell lymphoma and follicular lymphoma) and JAM-C+ ones (hairy cell leukemia, marginal zone B-cell lymphoma). Therefore, we propose JAM-C as a new identification tool in B-cell lymphoma diagnosis.

Immune-privileged embryonic Swiss mouse STO and STO cell-derived progenitor cells: major histocompatibility complex and cell differentiation antigen expression patterns resemble those of human embryonic stem cell lines

Embryonic mouse STO (S, SIM; T, 6-thioguanine resistant; O, ouabain resistant) and 3(8)21-enhanced green fluorescent protein (EGFP) cell lines exhibit long-term survival and hepatic progenitor cell behaviour after xenogeneic engraftment in non-immunosuppressed inbred rats, and were previously designated major histocompatibility complex (MHC) class I- and class II-negative lines. To determine the molecular basis for undetectable MHC determinants, the expression and haplotype of H-2K, H-2D, H-2L and I-A proteins were reassessed by reverse transcriptase-polymerase chain reaction (RT-PCR), cDNA sequencing, RNA hybridization, immunoblotting, quantitative RT-PCR (QPCR), immunocytochemistry and flow cytometry. To detect cell differentiation (CD) surface antigens characteristic of stem cells, apoptotic regulation or adaptive immunity that might facilitate progenitor cell status or immune privilege, flow cytometry was also used to screen untreated and cytokine [interferon (IFN)-gamma]-treated cultures. Despite prior PCR genotyping analyses suggestive of H-2q haplotypes in STO, 3(8)21-EGFP and parental 3(8)21 cells, all three lines expressed H-2K cDNA sequences identical to those of d-haplotype BALB/c mice, as well as constitutive and cytokine-inducible H-2K(d) determinants. In contrast, apart from H-2L(d[LOW]) display in 3(8)21 cells, H-2Dd, H-2Ld and I-Ad determinants were undetectable. All three lines expressed constitutive and cytokine-inducible CD34; however, except for inducible CD117([LOW]) expression in 3(8)21 cells, no expression of CD45, CD117, CD62L, CD80, CD86, CD90.1 or CD95L/CD178 was observed. Constitutive and cytokine-inducible CD95([LOW]) expression was detected in STO and 3(8)21 cells, but not in 3(8)21-EGFP cells. MHC (class I(+[LOW])/class II-) and CD (CD34+/CD80-/CD86-/CD95L-) expression patterns in STO and STO cell-derived progenitor cells resemble patterns reported for human embryonic stem cell lines. Whether these patterns reflect associations with mechanisms that are regulatory of immune privilege or functional tissue-specific plasticity is unknown.

Expression and induction of collagenases (MMP-8 and -13) in plasma cells associated with bone-destructive lesions

Matrix metalloproteinases (MMPs) collectively degrade extracellular matrix and basement membrane proteins in chronic inflammation and bone-destructive lesions. This study examined the ability of immunoglobulin-producing plasma cells, typically present in sites of chronic inflammation, to express collagenases (MMP-8 and -13) in vivo and in vitro. Phorbol-12-myristate-13-acetate, interleukin-6, and tumour necrosis factor-alpha and heparin with the tumour promoter or cytokines potently enhanced (up to nine-fold) MMP-8 and -13 expression by the RPMI 8226 myeloma cell line, as evidenced by western blotting and semi-quantitative reverse transcriptase-polymerase chain reaction. Immunohistochemical analysis and in situ hybridization revealed that plasma cells expressed MMP-8 and -13 focally in periapical granulomas, odontogenic cysts, and malignant plasmacytomas. MMP-8 and MMP-13 from plasma cells can participate in bone organic matrix destruction at sites of chronic inflammation and neoplastic growth. Since MMP-13 was more frequently expressed than MMP-8 in plasma cells of strongly recurring keratocysts and malignant plasmacytomas, it is concluded that plasma cell MMP-13 has a particularly important role in benign and malignant bone-destructive lesions.

Immune regulation in multiple myeloma: the host-tumour conflict

Multiple myeloma (MM) remains essentially incurable by conventional anti-tumour therapy. This has led to increased interest in the possibility that forms of immune therapy might be effective. The successful use of donor lymphocyte infusions (DLI) in a few cases of MM relapse following allogeneic bone marrow transplantation have added weight to this view. MM is characterized by several defects in the host's immune system. The influence of the malignant clone on the function of the immune effector cells results from both passive and active suppression. Despite an array of functional adhesion molecules and HLA class I and II molecules on their surface and the secretion of a tumour-specific peptide, they fail to express adequate levels of co-stimulatory molecules thus inducing anergy in potentially tumour-specific T cells. In addition to this passive evasion of immune regulation, MM tumour cells are capable of producing a number of immunologically active agents which can induce immunosuppression such as transforming growth factor-beta, Fas ligand (FasL), vascular endothelial growth factor and Muc-1. It is postulated that these agents may be produced by the tumour cell to influence the microenvironment to support growth and differentiation of the clone but may have the additional benefit of altering the function of the host immune effector cells and thus preventing tumour rejection. This duality of function is important if clinicians are to design immunotherapy strategies which will achieve the true potential and result in improved survival in MM.

Detection of Functional Platelet-Activating Factor Receptors on Human Tonsillar B Lymphocytes

Although platelet-activating factor (PAF) receptors have been found on B lymphoblastoid cell lines, the action of PAF on freshly isolated human B cells has not been clearly demonstrated. Using a sensitive semiquantitative reverse-transcriptase PCR, we have found PAF receptor mRNA expressed by tonsillar B lymphocytes, but little in T lymphocytes. Examination of Percoll-fractionated tonsillar B cells indicated that the low density (primarily germinal center cells) and medium density fractions had approximately twofold more PAF receptor mRNA relative to the high density fraction. PAF (10−7 M) stimulated increases in intracellular Ca2+ that were consistently higher in the low and medium density B lymphocytes compared with high density cells. The PAF receptor antagonist Web 2170 inhibited this. Addition of PAF, but not lyso- or enantio-PAF, induced four- to sixfold greater synthesis of IgM and IgG in low and medium density cells compared with unstimulated controls, but had little effect on Ig production by high density cells. To investigate how PAF may influence Ig synthesis, PAF-stimulated B cells were examined for production of the Th2-type cytokines IL-4 and IL-13. PAF induced IL-4 and IL-13 mRNA expression in 17% of CD20+ cells, and IL-4 was detected in cell supernatants after 48–72 h of culture. Together, these data strongly suggest that functional PAF receptors are expressed on B cells in tonsils.

Expression of matrix metalloproteinases by human plasma cells and B lymphocytes

Matrix metalloproteinases (MMP) are proteolytic enzymes that play a key role in tissue remodelling during physiological and pathological processes, by initiating the degradation of extracellular matrix. MMP overexpression can lead to tissue destruction which is characteristic of chronic inflammatory diseases such as rheumatoid arthritis and scleritis. Plasma cells are often abundant at such sites of chronic inflammation. In the present study we investigated whether plasma cells could contribute to matrix degradation by their expression of MMP In situ hybridization and immunohistochemical analyses on diseased synovial and scleral tissue demonstrated the expression of stromelysin-1 (MMP-3) and gelatinase B (MMP-9), but little or no tissue inhibitor of matrix metalloproteinase 1 (TIMP-1) mRNA, by IgG-positive plasma cells. Northern blot analysis of RNA extracted from a human plasma cell line (ARH-77), Epstein-Barr virus-transformed B cells, and purified peripheral blood B cells, demonstrated expression of stromelysin mRNA. TIMP-1 mRNA was only detected by the more sensitive reverse transcription PCR method in these cell types. Plasma cells and B lymphocytes cultured in the presence of monensin demonstrated cytoplasmic gelatinase B. Gelatin and casein zymography on conditioned media (CM) derived from cytokine treated plasma cells revealed the induction of secreted gelatinase and stromelysin activity. Western blotting confirmed the presence of stromelysin-1 and TIMP-1 proteins in plasma cell CM. These data suggest that plasma cells are not only capable of modulating an inflammatory response by antibody and cytokine production, but also by their ability to produce MMP. Secretion of MMP from focal aggregates of plasma cells may play a critical role in tissue destructive diseases such as rheumatoid synovitis and scleritis.

Decreased Production of TGF-β by Lymphocytes from Patients with Systemic Lupus Erythematosus

TGF-β has marked inhibitory effects on the immune system but also serves as a costimulatory factor in the development of T cells with down-regulatory activities. This cytokine is secreted as a latent complex and converted extracellularly to its active form. We have recently learned that anti-CD2 is a potent inducer of lymphocyte-derived TGF-β and that NK cells are the predominant source. The objective of this study was to compare levels of constitutive, anti-CD2-induced and cytokine-regulated TGF-β produced by blood lymphocytes from patients with systemic lupus erythematosus (SLE) in comparison with healthy controls. Using a highly sensitive and specific bioassay to assess TGF-β, we report that unstimulated PBL from SLE patients, especially the NK cell subset, produced decreased levels of active TGF-β. In response to anti-CD2, concentrations of active and total TGF-β were also decreased in SLE. After learning that IL-2 and TNF-α enhance lymphocyte production of active TGF-β, we found that the addition of these cytokines was unable to increase active TGF-β to normal concentrations. Although we observed that IL-10 inhibited the production of active TGF-β, antagonism of this cytokine was unable to completely correct the defect. In two SLE patients with B cell hyperactivity, spontaneous IgG production was almost abolished by the combination of TGF-β and IL-2. Therefore, decreased production of each of these cytokines in SLE could be important in the perpetuation of B cell hyperactivity.

Increased in vitro induced CD4+ and CD8+ T cell IFN-gamma and CD4+ T cell IL-10 production in stable relapsing multiple sclerosis

Multiple sclerosis (MS) is presumed to be a T-cell mediated chronic inflammatory disease of the central nervous system. Investigators previously demonstrated increased IFN-gamma (pro-inflammatory) and IL-10 (counterregulatory anti-inflammatory) in MS. The balance of pro-inflammatory and counterregulatory anti-inflammatory cytokines may be important in the stabilization of disease activity. Purified CD4+ and CD8+ T cells from patients with clinically definite, stable relapsing MS (RRMS) were stimulated by anti-CD3 mAb or Con A for 48 hours and cytokine supernatants analysed for production of IL-2, IL-6, IFN-gamma, TNF-alpha (potential pro-inflammatory) and IL-4, IL-10, and TGF-beta (potential counterregulatory anti-inflammatory). Con A activated CD4+ and CD8+ T cell proinflammatory cytokine IL-2 secretion, CD4+ T cell IL-6 secretion, CD4+ and CD8+ T cell TNF-alpha secretion and CD8+ T cell IFN-gamma secretion was decreased significantly in RRMS subjects compared to controls. CD3 activated CD4+ and CD8+ T cell IL-6 secretion and CD4+ T cell TNF-alpha secretion was significantly decreased in MS subjects compared to controls. In contrast, there was increased CD3-induced IFN-gamma in both CD4+ and CD8+ T cells and counterregulatory anti-inflammatory CD3-induced IL-10 secretion in CD4+ T cells in RRMS compared to controls. These data suggest that an equilibrium of a pro-inflammatory (IFN-gamma) and a counterregulatory anti-inflammatory (IL-10) cytokine may define stable clinically definite early RRMS.

Profile of cytokine mRNA expression in spontaneous and UV-induced skin lesions from actinic prurigo patients

BACKGROUND

Actinic prurigo (AP) appears to be an immune-mediated disease triggered by exposure to ultraviolet light (UV).

OBJECTIVE

To assess the profile of cytokine production in skin lesions from AP patients.

METHODS

The cytokine production (IL-1 beta, IL-2, IL-4, IL-6, IL-10, IL-13, TNF-alpha, IFN-tau, and TGF-beta) in skin biopsies from 12 AP lesions was determined by a semiquantitative coupled reverse transcription-polymerase chain reaction.

RESULTS

We found expression of TGF-beta and IL-13 genes in most AP skin lesions; IL-1 beta, IL-6, TNF-alpha, IFN-tau, and IL-10 were detected in some of these specimens. However, the levels of expression of all cytokines studied were not significantly different in AP skin lesions compared to nonlesional skin.

CONCLUSIONS

TGF-beta and IL-13 might have a key role in both the inflammatory phenomenon and absence of significant expression of most cytokines in AP skin. The cytokine production in AP skin resembles that observed in rheumatoid synovium, a paucity in cytokine expression despite the presence of infiltrating activated mononuclear cells.

Human naive B cells cultured with EL-4 T cells mimic a germinal center-related B cell stage before generating plasma cells. Concordant changes in Bcl-2 protein and messenger RNA levels

The T cell-dependent B cell response in vivo occurs in organized microenvironments. Alternative routes exist in that early plasma cells are generated in the T zone while others emerge later from the germinal center (GC) reaction. We investigated whether B cell stages resembling those defined in vivo/ex vivo might be induced in an in vitro system in which naive human B cells are activated by EL-4 T cells and cytokines. Adult peripheral blood- or cord blood-derived B cells were found to mimic an early activated stage (CD38(low), IgD+, increased CD5+) followed by a centroblastic GC-related stage (CD38(int), CD77+, CD95(Fas)+, Bcl-2 protein(low)) before differentiating into morphologically typical, CD38(high), Fas- plasma cells of an immature type (Bcl-2(low), VLA-5-). The GC-related cells and the plasma cells exhibited spontaneous apoptosis in medium, the former also undergoing anti-Fas antibody-induced apoptosis in medium as well as during CD40L exposure in the EL-4 cultures. These Bcl-2(low) cells maintained a high viability in contact with EL-4 cells. Thus, some, major B cell stages with typical functional features as described for cells in vivo/ex vivo are sequentially generated in this in vitro system and the kinetics of the changes can be analyzed in a synchronized cell population. With regard to previous apparently conflicting observations on the Bcl-2 mRNA level in GC B cells, we performed competitive reverse-transcription polymerase chain reaction. Concordant changes in Bcl-2 mRNA and protein levels were found, i.e. during Bcl-2 down-regulation in the GC-related B cells in ongoing EL-4 cultures or in medium, and during a more modest up-regulation upon contact with fresh EL-4 cells. Regulation of Bcl-2 protein, therefore, predominantly occurred at the mRNA steady-state level.