CD45 isoforms on human CD4+ T-cell subsets

Tetraspanin CD53 controls T cell immunity through regulation of CD45RO stability, mobility, and function

T cells depend on the phosphatase CD45 to initiate T cell receptor signaling. Although the critical role of CD45 in T cells is established, the mechanisms controlling function and localization in the membrane are not well understood. Moreover, the regulation of specific CD45 isoforms in T cell signaling remains unresolved. By using unbiased mass spectrometry, we identify the tetraspanin CD53 as a partner of CD45 and show that CD53 controls CD45 function and T cell activation. CD53-negative T cells (Cd53^-/-) exhibit substantial proliferation defects, and Cd53^-/- mice show impaired tumor rejection and reduced IFNγ-producing T cells compared with wild-type mice. Investigation into the mechanism reveals that CD53 is required for CD45RO expression and mobility. In addition, CD53 is shown to stabilize CD45 on the membrane and is required for optimal phosphatase activity and subsequent Lck activation. Together, our findings reveal CD53 as a regulator of CD45 activity required for T cell immunity.

Dynamic intron retention modulates gene expression in the monocytic differentiation pathway

Monocytes play a crucial role in maintaining homeostasis and mediating a successful innate immune response. They also act as central players in diverse pathological conditions, thus making them an attractive therapeutic target. Within the bone marrow, monocytes arise from a committed precursor termed cMoP (Common Monocyte Progenitor). However, molecular mechanisms that regulate the differentiation of cMoP to various monocytic subsets remain unclear. Herein, we purified murine myeloid precursors for deep poly-A enriched RNA sequencing to understand the role of alternative splicing in the development and differentiation of monocytes under homeostasis. Our analyses revealed intron retention to be the major alternative splicing mechanism involved in the monocyte differentiation cascade, especially in the differentiation of Ly6C^hi monocytes to Ly6C^lo monocytes. Furthermore, we found that the key genes regulated by intron retention in the differentiation of murine Ly6C^hi to Ly6C^lo monocytes were also conserved in humans. Our data highlight the unique role of intron retention in the regulation of the monocytic differentiation pathway.

An imbalance of esophageal effector and regulatory T cell subsets in experimental eosinophilic esophagitis in mice

We recently reported a critical role for T cells in the induction of eosinophilic esophagitis (EE) in mice; however, the role of specific T cell subsets in disease pathogenesis is not yet understood. In the current study, we tested the hypothesis that allergen-induced EE develops in response to the disproportion of functionally different effector and regulatory T cells in the esophagus. Fluorescence-activated cell sorter analysis was performed to examine activated T cell subsets using the cell surface activation markers CD25 and CD69. A significant increase in activated CD4(+) and CD4(-) T cells was observed in the total esophageal cells isolated from the mouse model of EE. Furthermore, an imbalance in the effector and regulatory T cells was observed in the esophagus. The esophageal CD4(+)CD45RB(high) effector T cells in allergen-challenged mice increased compared with saline-challenged mice (65.4 +/- 3.6 x 10(3) to 44.8 +/- 4.2 x 10(3)), whereas CD4(+)CD45RB(low) mostly regulatory T cells decreased in allergen-challenged mice compared with saline-challenged mice (5.8 +/- 0.9 x 10(3) from 10.2 +/- 1.7 x 10(3)). The functional characteristics were examined by analysis of the pro- and anti-inflammatory cytokine profile of purified low and high CD4(+)CD45RB subsets from the spleen. Additionally, a significantly reduced interleukin (IL)-2 production by CD4(+)CD45RB(low) cells in allergen-challenged mice compared with saline-challenged mice was observed. The reduced IL-2 in the CD4(+)CD45RB(low) subset may be associated with reduction of CD4(+)CD45RB(low) subset. In conclusion, our results suggest that local regulatory interaction of CD45RB(high) and CD45RB(low) CD4(+) T cells may be required for protective and pathogenic immunity in EE.

Antibody-induced transplantation tolerance that is dependent on thymus-derived regulatory T cells

Targeting of the CD45RB isoform by mAb (anti-CD45RB) effectively induces donor-specific tolerance to allografts. The immunological mechanisms underlying the tolerant state remain unclear although some studies have suggested the involvement of regulatory T cells (T-regs). Although their generative pathway remains undefined, tolerance promoting T-regs induced by systemic anti-CD45RB treatment have been assumed to originate in the peripheral immune system. We demonstrate herein that separable effects on the peripheral and central immune compartments mediate graft survival induced by anti-CD45RB administration. In the absence of the thymus, anti-CD45RB therapy is not tolerogenic though it retains peripheral immunosuppressive activity. The thymus is required for anti-CD45RB to produce indefinite graft survival and donor-specific tolerance, and this effect is accomplished through thymic production of donor-specific T-regs. These data reveal for the first time an Ab-based tolerance regimen that relies on the central tolerance pathway.

An anti-CD45RO/RB monoclonal antibody modulates T cell responses via induction of apoptosis and generation of regulatory T cells

The effects of a chimeric monoclonal antibody (chA6 mAb) that recognizes both the RO and RB isoforms of the transmembrane protein tyrosine phosphatase CD45 on human T cells were investigated. Chimeric A6 (chA6) mAb potently inhibited antigen-specific and polyclonal T cell responses. ChA6 mAb induced activation-independent apoptosis in CD4⁺CD45RO/RB^high T cells but not in CD8⁺ T cells. In addition, CD4⁺ T cell lines specific for tetanus toxoid (TT) generated in the presence of chA6 mAb were anergic and suppressed the proliferation and interferon (IFN)-γ production by TT-specific effector T cells by an interleukin-10–dependent mechanism, indicating that these cells were equivalent to type 1 regulatory T cells. Similarly, CD8⁺ T cell lines specific for the influenza A matrix protein-derived peptide (MP.58-66) generated in the presence of chA6 mAb were anergic and suppressed IFN-γ production by MP.58-66–specific effector CD8⁺ T cells. Furthermore, chA6 mAb significantly prolonged human pancreatic islet allograft survival in nonobese diabetic/severe combined immunodeficiency mice injected with human peripheral blood lymphocytes (hu-PBL-NOD/SCID). Together, these results demonstrate that the chA6 mAb is a new immunomodulatory agent with multiple modes of action, including deletion of preexisting memory and recently activated T cells and induction of anergic CD4⁺ and CD8⁺ regulatory T cells.

Expression of CD45RB functionally distinguishes intestinal T lymphocytes in inflammatory bowel disease

The importance of CD45RB expression on T cells was already shown in mice where CD45RB(high) expression determines pathogenic potential. In this study, we analyzed the expression of CD45RA, CD45RB, and CD45RO on CD4(+) T lymphocytes in the intestinal mucosa and in the circulation of patients with inflammatory bowel disease (IBD). In addition, we studied the cytokine profile of these cells. In the circulation, virtually all CD4(+)CD45RB(high) T cells expressed the naive marker CD45RA, and circulating CD4(+)CD45RB(low) cells expressed the memory marker CD45RO in IBD patients and a control patient population. In contrast, the intestinal CD4(+) CD45RB(high) T cells are in normal controls for 90% CD45RO(+). However, in IBD, 27.7% [Crohn's disease (CD)] and 49% [ulcerative colitis (UC)] of the intestinal CD4(+) CD45RB(high) T cells are CD45RA(+). This special CD4CD45RA(+) T cell in IBD can be found in the lamina propria as well as in lymphoid follicles (confocal laser-scanning microscopy). The CD4(+)CD45RB(high) T lymphocytes produce significantly less interleukin (IL)-10 and IL-4 and produce more tumor necrosis factor alpha than CD45RB(low) T lymphocytes in control patients. CD4(+)CD45RB(low) T cells from IBD patients produced less IL-10 than CD4(+)CD45RB(low) T lymphocytes of controls, and interferon-gamma production by both T lymphocyte subsets was decreased in IBD. These data indicate that CD and UC are characterized by an influx of CD4(+)CD45RB(high) T lymphocytes. These CD4(+)CD45RB(high) T lymphocytes seem to be important in the pathogenesis of IBD, as they produce more proinflammatory cytokines and less anti-inflammatory cytokines compared with CD4(+)CD45RB(low) T lymphocytes.

Distinct gene expression profiles of human type 1 and type 2 T helper cells

BACKGROUND

The development and activation of CD4+ helper T cell (Th) subsets with distinct patterns of unbalanced production of cytokines play an important part in infectious, allergic and autoimmune diseases. Human neonatal cord blood CD4+ Th cells can be polarized into type 1 or type 2-like effector cells in vitro by culturing them in the presence of interleukin (IL)-12 or IL-4, respectively. We have exploited this experimental system to identify marker genes that are differentially expressed by polarized Th1 and Th2 cells. An oligonucleotide microarray specifically designed to screen for inflammation-related candidate genes was used and the differential expression was further validated with a quantitative real-time RT-PCR method.

RESULTS

In addition to the previously described marker genes of Th cells, we report subtle changes in the expression of several other genes that represent growth factors, receptors and other signaling molecules in polarized Th1 and Th2 cell subsets. Additionally, we describe a novel set of genes as Th1/Th2 differentiation markers for cells activated by anti-CD3 and anti-CD28 antibodies.

CONCLUSIONS

This study demonstrates the power of the targeted use of microarrays in combination with quantitative real-time RT-PCR in identifying and validating new marker genes for gene expression studies.

The role of CD45 and CD45-associated molecules in T cell activation

CD45 (lymphocyte common antigen) is a receptor-linked protein tyrosine phosphatase that is expressed on all leucocytes, and which plays a crucial role in the function of these cells. On T cells the extracellular domain of CD45 is expressed in several different isoforms, and the particular isoform(s) expressed depends on the particular subpopulation of cell, their state of maturation, and whether or not they have previously been exposed to antigen. It has been established that the expression of CD45 is essential for the activation of T cells via the TCR, and that different CD45 isoforms display a different ability to support T cell activation. Although the tyrosine phosphatase activity of the intracellular region of CD45 has been shown to be crucial for supporting signal transduction from the TCR, the nature of the ligands for the different isoforms of CD45 have been elusive. Moreover, the precise mechanism by which potential ligands may regulate CD45 function is unclear. Interestingly, in T cells CD45 has been shown to associate with numerous molecules, both membrane associated and intracellular; these include components of the TCR-CD3 complex and CD4/CD8. In addition, CD45 is reported to associate with several intracellular protein tyrosine kinases including p56lck and p59fyn of the src family, and ZAP-70 of the Syk family, and with numerous proteins of 29-34 kDa. These CD45-associated molecules may play an important role in regulating CD45 tyrosine phosphatase activity and function. However, although the role of some of the CD45-associated molecules (e.g. CD45-AP and LPAP) has become better understood in recent years, the role of others still remains obscure. This review aims to summarize recent findings on the role of CD45 and CD45-associated molecules in T cell activation, and to highlight issues that seem relevant to ongoing research in this area.