Dual CD45RA, CD45RO positive T-lymphocytes within rheumatoid arthritic joints

Reciprocal activation of CD4+ T cells and synovial fibroblasts by stromal cell-derived factor 1 promotes RANKL expression and osteoclastogenesis in rheumatoid arthritis

OBJECTIVE

Stromal cell-derived factor 1 (SDF-1) is a chemokine that is involved in the bone-destructive process in rheumatoid arthritis (RA) and bony metastasis in malignancy. This study was undertaken to determine the role and mechanism of SDF-1 in RA-associated osteoclastogenesis.

METHODS

The expression of SDF-1, tumor necrosis factor α (TNFα), and RANKL in RA synovial tissue was analyzed using confocal microscopy. After synovial fibroblasts and CD4+ T cells were treated with SDF-1, RANKL messenger RNA expression was determined by real-time and reverse transcription polymerase chain reaction. Osteoclastogenesis was assessed by counting tartrate-resistant acid phosphatase-positive multinucleated cells in CD14+ monocytes cultured with SDF-1 in the presence of anticytokine antibodies or signal inhibitors and in monocytes cocultured with SDF-1-pretreated synovial fibroblasts and CD4+ T cells.

RESULTS

RANKL, TNFα, and SDF-1 were coexpressed in the lining and sublining of RA synovium. SDF-1 stimulated RANKL expression in RA synovial fibroblasts and CD4+ T cells, and TNFα inhibition reduced this stimulation. When monocytes isolated from human peripheral blood were cultured with SDF-1, they were differentiated into osteoclasts in the absence of RANKL. Monocytes were also differentiated into osteoclasts when they were cocultured with SDF-1-pretreated synovial fibroblasts or CD4+T cells; however, this osteoclastogenesis was reduced by TNFα inhibition.

CONCLUSION

Our findings indicate that SDF-1 induces osteoclastogenesis directly and indirectly via up-regulating RANKL expression in RA synovial fibroblasts and CD4+ T cells, and that this is mediated by TNFα. The axis of SDF-1 and RANKL is a potential therapeutic target for RA-associated bone destruction.

Immune reconstitution following rabbit antithymocyte globulin

Depletional induction therapies are routinely used to prevent acute rejection and improve transplant outcome. The effects of depleting agents on T-cell subsets and subsequent T-cell reconstitution are incompletely defined. We used flow cytometry to examine the effects of rabbit antithymocyte globulin (rATG) on the peripheral T-cell repertoire of pediatric and adult renal transplant recipients. We found that while rATG effectively depleted CD45RA+CD27+ naïve and CD45RO+CD27+ central memory CD4+ T cells, it had little effect on CD45RO+CD27- CD4+ effector memory or CD45RA+CD31-, CD45RO+CD27+ and CD45RO+CD27- CD8+ T cell subsets. When we performed a kinetic analysis of CD31+ recent thymic emigrants and CD45RA+/RO+ T cells, we found evidence for both thymopoiesis and homeostatic proliferation contributing to immune reconstitution. We additionally examined the impact of rATG on peripheral CD4+Foxp3+ T cells. We found that in adults, administration of rATG-induced peripheral expansion and new thymic emigration of T cells with a Treg phenotype, while CD4+Foxp3+ T cells of thymic origin predominated in children, providing the first evidence that rATG induces Treg in vivo. Collectively our data indicate that rATG alters the balance of regulatory to memory effector T cells posttransplant, providing an explanation for how it positively impacts transplant outcome.

Up-regulation of stromal cell-derived factor 1 (CXCL12) production in rheumatoid synovial fibroblasts through interactions with T lymphocytes: role of interleukin-17 and CD40L-CD40 interaction

OBJECTIVE

Stromal cell-derived factor 1 (SDF-1) is a potent chemoattractant for memory T cells in inflamed rheumatoid arthritis (RA) synovium. This study was undertaken to investigate the effect of interleukin-17 (IL-17) and CD40-CD40L interaction on SDF-1 production in RA fibroblast-like synoviocytes (FLS).

METHODS

Synovial fluid (SF) and serum levels of SDF-1 in RA patients were measured by enzyme-linked immunosorbent assay (ELISA). The SDF-1 produced by cultured RA FLS was evaluated by real-time polymerase chain reaction and ELISA after FLS were treated with IL-17 and inhibitors of intracellular signal molecules. The SDF-1 level was also determined after FLS were cocultured with T cells in the presence and absence of IL-17.

RESULTS

Concentrations of SDF-1 in the sera and SF were higher in RA patients than in osteoarthritis patients, although the increase in the serum levels did not reach statistical significance. The production of SDF-1 in RA FLS was enhanced by IL-17 stimulation. This effect of IL-17 was blocked by inhibitors of phosphatidylinositol 3-kinase (PI 3-kinase), NF-kappaB, and activator protein 1 (AP-1). When FLS were cocultured with T cells, SDF-1 production was up-regulated, especially in the presence of IL-17, but FLS were inhibited by neutralizing anti-IL-17 and anti-CD40L antibodies. Addition of RA SF to cultured RA FLS significantly up-regulated SDF-1 messenger RNA expression, which was hampered by pretreatment with anti-IL-17 antibody.

CONCLUSION

SDF-1 is overproduced in RA FLS, and IL-17 could up-regulate the expression of SDF-1 in RA FLS via pathways mediated by PI 3-kinase, NF-kappaB, and AP-1. Our findings suggest that inhibition of the interaction between IL-17 from T cells and SDF-1 in FLS may provide a new therapeutic approach in RA.

Selective lymphocyte chemokine receptor expression in the rheumatoid joint

OBJECTIVE

In patients with rheumatoid arthritis (RA), chemokines and their receptors are important for lymphocyte trafficking into the inflamed joint. This study was undertaken to characterize the expression of chemokine receptors CCR1, CCR2, CCR3, CCR4, CCR5, CCR6, CXCR3, and CX3CR1 in normal (NL) peripheral blood (PB), RA PB, and RA synovial fluid (SF).

METHODS

Using flow cytometry, immunohistochemistry, and 2-color immunofluorescence, we defined the expression of chemokine receptors on CD3+ T lymphocytes in RA synovial tissue (ST), RA SF, RA PB, and NL PB.

RESULTS

The percentage of CD3+ lymphocytes expressing CCR2, CCR4, CCR5, and CX3CR1 was significantly elevated in RA PB compared with that in NL PB, while the percentage of CD3+ lymphocytes expressing CCR5 was significantly enhanced in RA SF compared with that in NL and RA PB. In contrast, similar percentages of CD3+ lymphocytes in NL PB, RA PB, and RA SF expressed CCR6 and CXCR3. Immunohistochemistry of RA ST showed lymphocyte expression of CCR4, and 2-color immunofluorescence staining revealed RA ST CD3+ lymphocytes intensely immunoreactive for CXCR3, suggesting that these 2 receptors may be particularly important for CD3+ lymphocyte trafficking to the inflamed joint. In comparisons of chemokine receptor expression on naive (CD45RA+) and memory (CD45RO+) CD3+ lymphocytes, there were greater percentages of memory CD3+/CD4+ lymphocytes expressing CCR4, CCR5, and CXCR3 than naive CD3+/CD4+ lymphocytes in RA PB and RA SF, and greater percentages of memory CD3+/CD8+ lymphocytes expressing CCR4, CCR5, and CXCR3 than naive CD3+/CD8+ lymphocytes in RA SF, suggesting receptor up-regulation upon lymphocyte activation. In contrast, percentages of CD3+/CD8+ memory lymphocytes expressing CX3CR1 were significantly less than percentages of naive CD3+/CD8+ lymphocytes in RA PB, suggesting that this receptor may be down-regulated upon lymphocyte activation. A major difference between the RA PB and NL PB groups was significantly more CCR4+ memory leukocytes and memory CCR5+/ CD3+/CD8+ lymphocytes in RA PB than NL PB, further suggesting that these receptors may be particularly important for lymphocyte homing to the RA joint.

CONCLUSION

These results identify CCR4, CCR5, CXCR3, and CX3CR1 as critical chemokine receptors in RA.

The autoimmune pathogenesis of rheumatoid arthritis: role of autoreactive T cells and new immunotherapies

OBJECTIVES

To review the role of T lymphocytes in the pathogenesis of rheumatoid arthritis (RA) and discuss the relevance of the components of the trimolecular complex (synovial T cells, autoantigens, and antigen presenting cells) in the pathogenic autoimmune response in RA.

METHODS

Currently available experimental data are combined into a hypothetical pathway that may explain some of the events in the RA process. The literature regarding the potential therapeutic strategies that interfere with specific components of the trimolecular complex and other mediators are discussed briefly.

RESULTS

T cells are activated in the peripheral blood, cross the endothelial cell wall, and migrate into the joints. Once in the synovial joints, T cells are reactivated by cross-reactive antigens and clonally expand. Clonally expanded T cells accumulate in the diseased joint and secrete proinflammatory cytokines that attract and activate other cells, such as monocytes and macrophages. Treatment with anti-CD4 monoclonal antibodies or anticytokine agents that prevents antigen presentation and/or T-cell activation were effective in RA. Other therapies, such as T-cell vaccination and T-cell receptor peptide vaccination targeting autoreactive T cells, showed clinical improvement, suggesting a pathogenic role of these lymphocytes in disease progression.

CONCLUSION

T cells appear to be actively involved in the pathogenesis of RA, but several parts of the pathway are hypothetical and further research is needed.

Marked increase in L-selectin-negative T cells in neonatal pertussis. The lymphocytosis explained?

The detailed immunophenotype of peripheral blood lymphocytes from a neonate with pertussis was determined by flow cytometry and compared with results from cord blood from healthy newborns. Most (72%) of the lymphocytes were CD3+ T cells with a normal CD4/CD8 ratio (2.5). The T cells were largely HLA-DR negative and CD45RA+, consistent with unstimulated naïve T cells. Almost all of the CD4+ T cells were Leu8 (L-selectin, CD62L) negative, while almost all of the CD8+ T cells were CD28+. There was no increase in CD7- CD4+ T cells (Th2-like). No relative increase in CD16/56+ NK cells (5%) or CD19/20+ B cells was seen. The most dramatic finding in this case was the remarkable lack of expression of L-selectin by the T cells. L-selectin expression is associated with homing of peripheral blood lymphocytes to lymph nodes. The dramatic reduction in L-selectin expression of the T lymphocytes in pertussis, perhaps induced by pertussis toxin, likely prevents homing of the T cells to peripheral lymphoid tissues and provides a likely explanation for the marked lymphocytosis noted in this disease.

Co-expression of the CD45RA and CD45RO antigens on T lymphocytes in chronic arthritis

The site of T lymphocyte activation in chronic arthritis is unknown. Peripheral blood (PB) lymphocytes from chronic arthritis patients are in a 'naive' or non-activated state, as defined by expression of the CD45RA antigen and lack of HLA class II expression. In contrast, most synovial fluid (SF) T lymphocytes express a 'memory' or activated phenotype, as defined by the CD45RO antigen and high HLA class II expression. Following stimulation, naive cells lose CD45RA and gain CD45RO expression to become memory cells with a transitional stage of dual CD45RA, CD45RO antigen expression. To localize where this change in phenotype occurs we used dual colour immunofluorescence labelling to compare the percentage of dual CD45RA, CD45RO-positive T lymphocytes in PB and SF from chronic arthritic patients and from normal PB, assuming this population would be increased at the primary site of T lymphocyte activation. Expression of the intermediate and late activation marker, HLA-DR, was also analysed using dual colour immunofluorescence labelling. The percentage of dual positive T lymphocytes was similar between arthritic PB, SF, and normal PB, as was the density of both CD45RA and CD45RO antigens. Thus, CD45 isoform expression did not indicate where T lymphocytes were activated. However, we identified a previously unreported population of CD45RA+ CD45RO+ HLA-DR- T lymphocytes in arthritic and normal PB. In SF, this population was absent, but a substantial number of dual CD45RA, CD45RO-positive HLA-DR+ T lymphocytes were identified. This population would not be predicted by the current model of T lymphocyte activation. Division of T lymphocytes into functional groups on the basis of CD45 isoform expression is likely to be more complicated than previously thought. Based on our findings we propose an alternative model of T lymphocyte differentiation.