John Prehn

The Role of Thymus-Expressed Chemokine and Its Receptor CCR9 on Lymphocytes in the Regional Specialization of the Mucosal Immune System

Chemokines play an important role in the migration of leukocytes at sites of inflammation, and some constitutively expressed chemokines may direct lymphocyte trafficking within lymphoid organs and peripheral tissues. Thymus-expressed chemokine (TECK or Ckβ-15/CCL25), which signals through the chemokine receptor CCR9, is constitutively expressed in the thymus and small intestine but not colon, and chemoattracts a small fraction of PBLs that coexpress the integrin α4β7. Here we show that TECK is expressed in the human small bowel but not colon by endothelial cells and a subset of cells in intestinal crypts and lamina propria. CCR9 is expressed in the majority of freshly isolated small bowel lamina propria mononuclear cells (LPMC) and at significantly higher levels compared with colonic LPMC or PBL. TECK was selectively chemotactic for small bowel but not colonic LPMC in vitro. The TECK-induced chemotaxis was sensitive to pertussis toxin and partially inhibited by Abs to CCR9. TECK attracts predominantly the T cell fraction of small bowel LPMC, whereas sorted CD3+CCR9+ and CD3+CCR9− lymphocytes produce similar Th1 or Th2 cytokines at the single cell level. Collectively, our data suggest that the selective expression of TECK in the small bowel underlie the homing of CCR9+ intestinal memory T cells to the small bowel rather than to the colon. This regional specialization implies a segregation of small intestinal from colonic immune responses.

TL1A Synergizes with IL-12 and IL-18 to Enhance IFN-γ Production in Human T Cells and NK Cells

TL1A, a recently described TNF-like cytokine that interacts with DR3, costimulates T cells and augments anti-CD3 plus anti-CD28 IFN-γ production. In the current study we show that TL1A or an agonistic anti-DR3 mAb synergize with IL-12/IL-18 to augment IFN-γ production in human peripheral blood T cells and NK cells. TL1A also enhanced IFN-γ production by IL-12/IL-18 stimulated CD56+ T cells. When expressed as fold change, the synergistic effect of TL1A on cytokine-induced IFN-γ production was more pronounced on CD4+ and CD8+ T cells than on CD56+ T cells or NK cells. Intracellular cytokine staining showed that TL1A significantly enhanced both the percentage and the mean fluorescence intensity of IFN-γ-producing T cells in response to IL-12/IL-18. The combination of IL-12 and IL-18 markedly up-regulated DR3 expression in NK cells, whereas it had minimal effect in T cells. Our data suggest that TL1A/DR3 pathway plays an important role in the augmentation of cytokine-induced IFN-γ production in T cells and that DR3 expression is differentially regulated by IL-12/IL-18 in T cells and NK cells.

The T Cell Costimulator TL1A Is Induced by FcγR Signaling in Human Monocytes and Dendritic Cells

The recently described TL1A/DR3 ligand/receptor pair mediates strong costimulation of Th1 cells. Activation of T and NK cells induces DR3 expression, permitting soluble recombinant TL1A to increase IFN-γ production and proliferation of these cells. Gut T cells and macrophages express TL1A, especially in Crohn’s disease (CD), and there is a strong association between CD and tl1a single nucleotide polymorphisms. Murine studies implicate TL1A in gut inflammation. To determine whether professional T cell-activating cells can express TL1A, fresh blood monocytes and monocyte-derived dendritic cells were stimulated with various activating ligands, including TLR agonists, IFN-γ, and immune complexes. FcγR stimulation strongly induced TL1A mRNA in both cell types, which correlated with the detection of TL1A on the cell surface and in cell culture medium. TLR agonists capable of inducing IL-6 and TNF-α in monocytes and dendritic cells did not induce surface nor soluble TL1A. Furthermore, we demonstrate that TL1A production in monocytes leads to enhancement of T cell responses. The induction of TL1A on APCs via specific pathway stimulation suggests a role for TL1A in Th1 responses to pathogens, and in CD.

Dominant Role for TL1A/DR3 Pathway in IL-12 plus IL-18-Induced IFN-γ Production by Peripheral Blood and Mucosal CCR9+ T Lymphocytes

The TNF-like cytokine TL1A augments IFN-γ production by anti-CD3 plus anti-CD28 and IL-12/IL-18-stimulated peripheral blood (PB) T cells. However, only a small subset of PB T cells respond to TL1A stimulation with IFN-γ production. PB CCR9+ T cells represent a small subset of circulating T cells with mucosal T cell characteristics and a Th1/Tr1 cytokine profile. In the current study, we show that TL1A enhanced IFN-γ production by TCR- or CD2/CD28-stimulated CCR9+CD4+ PB T cells. However, TL1A had the most pronounced effect on augmenting IFN-γ production by IL-12/IL-18-primed CCR9+CD4+ PB T cells. TL1A enhanced both the percentage and the mean fluorescence intensity of IFN-γ in CCR9+CD4+ T cells as assessed by intracellular cytokine staining. IL-12 plus IL-18 up-regulated DR3 expression in CCR9+CD4+ T cells but had negligible effect on CCR9−CD4+ T cells. CCR9+CD4+ T cells isolated from the small intestine showed a 37- to 105-fold enhancement of IFN-γ production when TL1A was added to the IL-12/IL18 cytokine combination. Cell membrane-expressed TL1A was preferentially expressed in CCR9+CD4+ PB T cells, and a blocking anti-TL1A mAb inhibited IFN-γ production by cytokine-primed CCR9+CD4+ T cells by ∼50%. Our data show that the TL1A/DR3 pathway plays a dominant role in the ultimate level of cytokine-induced IFN-γ production by CCR9+ mucosal and gut-homing PB T cells and could play an important role in Th1-mediated intestinal diseases, such as Crohn’s disease, where increased expression of IL-12, IL-18, TL1A, and DR3 converge in the inflamed intestinal mucosa.

CC Chemokine Receptor 9 Expression Defines a Subset of Peripheral Blood Lymphocytes with Mucosal T Cell Phenotype and Th1 or T-Regulatory 1 Cytokine Profile

The chemokine receptor CCR9 is expressed on most small intestinal lamina propria and intraepithelial lymphocytes and on a small subset of peripheral blood lymphocytes. CCR9-expressing lymphocytes may play an important role in small bowel immunity and inflammation. We studied the phenotype and functional characteristics of CCR9+ lymphocytes in blood from normal donors. A subset of CCR9+ T cells have a phenotype of activated cells and constitutively express the costimulatory molecules CD40L and OX-40. In contrast to CCR9−, CCR9+CD4+ peripheral blood T cells proliferate to anti-CD3 or anti-CD2 stimulation and produce high levels of IFN-γ and IL-10. IL-10-producing cells were exclusively detected within the CCR9+ subset of CD4+ T cells by intracellular staining and were distinct from IL-2- and IFN-γ-producing cells. Moreover, memory CCR9+CD4+ lymphocytes respond to CD2 stimulation with proliferation and IFN-γ/IL-10 production, whereas memory CCR9−CD4+ cells were unresponsive. In addition, memory CCR9+CD4+ T cells support Ig production by cocultured CD19+ B cells in the absence of prior T cell activation or addition of exogenous cytokines. Our data show that the memory subset of circulating CCR9+CD4+ T cells has characteristics of mucosal T lymphocytes and contains cells with either Th1 or T-regulatory 1 cytokine profiles. Studies on the cytokine profile and Ag specificity of this cell subset could provide important insight into small intestinal immune-mediated diseases and oral tolerance in humans.

Expression and regulation of the chemokine receptor CXCR3 on lymphocytes from normal and inflammatory bowel disease mucosa.

Chemokine receptors play an important role in the recruitment of activated T cells to inflammatory sites. The aim of this study was to analyze the expression of the chemokine receptor CXCR3 on T lymphocytes in intestinal lymphoid tissues and to document the altered disposition of these cells in patients with inflammatory bowel disease (IBD). The expression and regulation of CXCR3 on mucosal lymphoid tissue and peripheral blood lymphocytes (PBLs) were analyzed by flow cytometry and Northern blotting. The migration of lamina propria lymphocytes (LPLs) and PBLs to interferon (IFN)-γ-inducible protein (IP)-10 (or CXCL10) was evaluated by chemotaxis assays. IFN-γ and interleukin-4–producing T lymphocytes were quantitated by intracellular staining, and IFN-γ was measured in culture supernatants by enzyme-linked immunosorbent assay. CXCR3 is expressed on the majority of CD4+ lamina propria (LP) T cells and correlates with a T-helper (Th) type 1/Th-0 cytokine phenotype on LP and mesenteric lymph node (MLN) CD4+ T lymphocytes. IP-10/CXCL10 is more chemotactic in vitro for both CD4+ and CD8+ T cells that have been isolated from the LP compared with peripheral blood. CXCR3 protein, but not messenger RNA, expression was lower in inflamed LPLs compared with uninvolved LPLs in patients with ulcerative colitis but not in those with Crohn’s disease. However, CXCR3 was expressed on a higher percentage of MLN CD4+ T cells isolated from inflamed intestinal tissue, and CXCR3 expression could be induced in vitro with T-cell activation in MLN CD4+ T cells. In summary, most CXCR3+ T lymphocytes in normal intestinal tissues are Th-1/Th-0 effector/memory cells. Activation-dependent receptor regulation and alteration in receptor-bearing cells, primarily in MLN draining inflamed intestinal tissue, suggest an important role for this T-cell subset in the pathogenesis of human IBD.

1,25-Dihydroxyvitamin-D3 regulation of interleukin-2 and interleukin-2 receptor levels and gene expression in human T cells

1,25-Dihydroxyvitamin-D3 (1,25-D3) is known to inhibit DNA synthesis, immunoglobulin and lymphokine production [interleukin-2 (IL-2), gamma interferon (G-IFN), and granulocyte-monocyte colony-stimulating factor (GM-CSF)] by mitogen-stimulated human peripheral blood mononuclear cells (PBMCs). Recent data suggest these inhibitory effects are mediated at the gene level through inhibition of mRNA accumulation of specific lymphokines in the activated cells. In previous studies, we have demonstrated the CD8+ T cell population was less sensitive to the anti-proliferative actions of 1,25-D3 than CD4+ T cells. The purpose of this investigation was to further assess ability of 1,25-D3 to regulate CD4+ and CD8+ T cell functions. Initial experiments showed that 1,25-D3 inhibited both IL-2 production and mRNA accumulation in mitogen-stimulated PBMC. However, IL-2 receptor (IL-2R) expression and mRNA accumulation in stimulated PBMC was not affected by 1,25-D3. Both FACS sorted CD4+ and CD8+ T cells expressed IL-2R equally upon stimulation and neither showed an inhibitory effect on this expression by 1,25-D3. Human CD4+ and CD8+ T cells showed a stimulus-specific production of IL-2. CD4+ cells stimulated with mitogen and HLA-DR positive accessory cells produced measurable levels of IL-2 that were completely inhibited by 1,25-D3. CD8+ T cells did not generate measurable amounts of IL-2 in this system. However, CD4+ and CD8+ T cells produced large amounts of IL-2 when stimulated with mitogen and a protein kinase C activator, phorbol myristate acetate (PMA). Under these circumstances, both CD4+ and CD8+ T cell IL-2 production was inhibited completely by 1,25-D3. These data suggest that IL-2R expression in PBMCs and T cell subsets is equal and unaffected by 1,25-D3 while IL-2 production in T cell subsets is stimulus-specific and completely inhibited by 1,25-D3.

TL1A Selectively Enhances IL-12/IL-18-Induced NK Cell Cytotoxicity against NK-Resistant Tumor Targets

IntroductionTL1A (TNFSF15) augments IFN-γ production by IL-12/IL-18 responsive human T cells. Its ligand, death domain receptor 3 (DR3), is induced by activation on T and NK cells. Although IL-12/IL-18 induces DR3 expression on most NK cells, addition of TL1A minimally increases IFN-γ production.Methods51Chromium release and flow cytometric analysis were used to determine whether the TL1A-DR3 pathway is implicated in tumor cell lysis. Our aim was to determine whether the TL1A-DR3 pathway is implicated in tumor cell lysis.ResultsTL1A had no additional effect on IL-12/IL-18-induced cytotoxicity against an NK-susceptible tumor (K562); however, it promoted cytotoxicity against NK-resistant targets susceptible to lysis only by activated NK cells.DiscussionWith IL-12/IL-18 activation, TL1A increased CD107a expression on NK cells which led to enhanced lysis of Daudi by PBMC and purified NK cells. To a lesser degree, TL1A increased lysis of colorectal adenocarcinoma epithelial derived lines (WiDr and SW837) by IL-12/IL-18-activated cells.ConclusionTL1A increased cytotoxicity of IL-12/IL-18-activated NK cells against target cells dependent on NK activation for lysis and could function in vivo as a key co-activator of NK cytotoxicity.

Potent inhibition of cytokine production from intestinal lamina propria T cells by phosphodiesterase-4 inhibitory thalidomide analogues.

In Crohns disease, intestinal lamina propria (LP) T cells overproduce TNF-α and IFN-γ, and clinical and animal studies indicate that this is pathogenic. Thalidomide influences cytokine production by leukocytes, inhibiting macrophage TNF-α, and is beneficial in treating Crohns disease. Chemical analogues have been synthesized that may lack teratogenic and other side effects of thalidomide. We tested three analogues [selective cytokine inhibitory drugs (SelCIDs) A, B, and C, all potent PDE4 inhibitors] for effect on TNF-α, IFN-γ, and IL-10 production by and on proliferation of intestinal LP mononuclear cells after T-cell stimulation and results were compared with those for peripheral blood leukocytes (PBL). While thalidomide itself had little effect, the SelCIDs were potent inhibitors, with relative inhibitory potencies: A≥B>>C. The LP T cells were less sensitive to inhibition by the SelCIDs than were PBL. Since highly pre-activated PBL were even less sensitive, activation state alone can account for the responsiveness of intestinal LP T cells. Thalidomide analogues could play a role in treating Crohns disease and other inflammatory disorders.

Serum interleukin-2 levels in a patient with focal segmental glomerulosclerosis: relationship to clinical course and cyclosporin A therapy

We describe a patient with steroid-resistant focal segmental glomerulosclerosis (FSGS) whose serum interleukin-2 (IL-2) levels were markedly elevated in association with disease activity. With cyclosporin A (CsA) treatment, the patient entered remission and serum IL-2 fell to undetectable levels. After cessation of CsA, the patient relapsed and the serum IL-2 levels were elevated again. Reinstitution of CsA therapy was followed by a partial remission and disappearance of detectable serum IL-2 levels.