The Journal of Immunology, 2006, 176: 1-2.
Copyright © 2006 by The American Association of Immunologists
IN THIS ISSUE
CXCL16 and GALT
Foreign macromolecules are recognized and taken up by M (membranous or microfold) cells within follicle-associated epithelium (FAE) on the luminal side of Peyer’s patches (PPs) and of isolated lymphoid follicles (ILFs) in small intestine mucosa. Although chemokines contribute to the spatial distribution of myeloid dendritic cells in PPs, it is not known if they attract lymphocytes. Hase et al. (p. 43
) used high-density oligonucleotide microarrays to analyze chemokine mRNA expression of mouse FAE and intestinal villous epithelial cells (IECs). CXCL16 mRNA expression was 5- to 15-fold higher in FAE vs IECs; in situ hybridization and immunohistochemistry localized CXCL16 distribution to the basolateral side of all regions of the FAE, including M cells, ILFs, and cecal patches but not IECs. A similar distribution was seen in biopsy samples of human terminal ileum. CXCR6, the receptor of CXCL16, was detected on most CD8+, and on some CD4+, T cells in PPs. Receptor-positive cells were CD44highCD62Llow, and CXCR6 expression was up-regulated by anti-CD3/CD28 mAb stimulation. Activated PP CD8+ and CD4+ T cells migrated in a chemotaxis assay in response to the N-terminal domain of CXCL16. PP T cells were found by anti-CD3
mAb staining to accumulate in the interfollicular region, in the subepithelial dome between FAE and lymphoid follicles, and in germinal centers of lymphoid follicles. Homing of injected fluorescence-labeled activated T cells to the subepithelial dome was inhibited and to the interfollicular region increased by prior injection of recipients with anti-CXCL16 mAb. The data suggest that membrane-bound CXCL16 mediates lymphocyte interactions with GALT epithelium.
T cell clonal expansion and aging
One consequence of aging is an increase in clonal expansion of single CD8+ T cells (TCEs) which could result from Ag-responding (AR-TCE) and/or Ag-independent (AI-TCE) mechanisms. To study TCE generation, Messaoudi et al. (p. 301
) determined that 39% of 20- to 24-mo-old wild-type mice had AI-TCEs identified by four-parameter analysis of TCRV
-chain usage, CDR3 length analysis, and surface expression of CD122 and CD44. AI-TCE incidence was reduced to 6.6% at 24 mo in MHC class I–/– mice, and all AI-TCEs had a CD4+ T cell phenotype. Mice deficient in MHC class II or CD8 had half the number of AI-TCEs whereas mice lacking only one MHC class I molecule had more AI-TCEs and enhanced homeostatic proliferation of CD4+ and CD8+ T cells than age-matched wild-type controls. Adult thymectomy produced greater naive T cell proliferation, as measured by BrdU incorporation, an earlier onset of AI-TCE and twice the incidence of AI-TCEs compared with wild-type animals. Levels of AI-TCEs in IL7R–/– mice reached 85–100% by 18 mo of age. Adjuvant-only treatment of wild-type mice increased AI-TCE frequency, but immunization with a viral Ag plus adjuvant did not elicit AR-TCE. The incidence of AI-TCEs was not affected in strains of mice transgenic for only a viral Ag-specific TCR 
or -chain. The authors conclude that the major mechanism in the formation of TCEs in mice is homeostatic and/or bystander proliferation independent of Ag.
Post-injury immunosuppression
Loss of T cell function occurs 
7 days after an injury. The Lederer laboratory showed that the loss is due to control of inflammatory reactions by regulatory CD4+CD25+ T (Treg) cells. In the follow-up to their study, Choileain et al. (p. 225
) looked at the increase in Treg activity following injury in a mouse burn model of tissue damage. Burn injury did not alter levels of FoxP3 mRNA or cell surface molecules in Treg or CD4+ CD25– T cells compared with sham-injured controls. However, draining lymph node, but not spleen, CD4+CD25+ T cells of burn mice suppressed anti-CD3 mAb-induced proliferation of CFSE-labeled CD4+CD25– T cells at day 7, but not at day 1, after injury. Transwell separation of the cell populations abrogated the suppression of anti-CD3 mAb-induced proliferation. Spleen or lymph node Treg cells isolated 7 days after burn injury produced high levels of IL-10 when stimulated with anti-CD3 mAb compared with controls. Addition of anti-TGF-1 mAb, but not anti-IL-10 mAb, to mixed cultures inhibited Treg suppression, and only the Treg cells showed an increase in cell surface TGF-1 expression after burn injury. Anti-CD3 mAb-stimulated production of IL-2 and IFN-
by naive lymph node cells was suppressed more by addition of lymph node Treg cells from burn mice than by those from sham mice. Increased expression of two T cell immune regulatory receptors was seen only on Treg cells at 7 days after burn injury. More IFN- was released from Ag-stimulated lymph node cells from sham or burn mice treated with anti-CD25 Ab before TNF-OVA immunization compared with controls. Treg depletion increased titers of IgG2a in the sham and burn mice. The authors propose that CD4+CD25+ T cells suppress the inflammatory response to burn injury and inhibit Th1-type immune function by a cell contact-dependent mechanism involving cell surface TGF-1.
Angiogenic activity of HMGB1
Extracellular high mobility group box-1 protein (HMGB1) acts as a signal of tissue injury and a mediator of inflammation. However, its involvement in angiogenesis has not been demonstrated. Mitola et al. (p. 12
) found that HMGB1 activated intracellular ERK1/2 in bovine aortic and murine endothelial cells in vitro. Its ability to induce a mitogenic response by the bovine cells was blocked by Ab against its receptor RAGE (receptor for advanced glycation end products). HMGB1 induced migration of bovine and mouse cells in a Boyden chamber assay, stimulated formation of cell sprouts from aggregates of mouse endothelial cells embedded in a three-dimensional fibrin gel, and induced formation of membrane ruffles at the edge of a mechanically wounded endothelial cell monolayer. Anti-RAGE Ab blocked ruffle formation and the appearance of numerous macroscopic blood vessels 72 h after implantation of HMGB1-loaded alginate beads onto chicken embryo chorioallantoic membranes (CAMs). RAGE expression on the surface of endothelial cells in the CAMs was detected by immunostaining. The data demonstrate the ability of HMGB1 to elicit a variety of activities associated with angiogenesis in vitro in bovine and mouse endothelial cells and in vivo in the chick embryo CAM.
Suppressing Th1 cell IL-2 production
The Hunter laboratory has shown that acute mortality of IL-27R–/– mice infected with Toxoplasma gondii is associated with increased IL-2 production. However, the impact of IL-27 production by APCs on IL-2 production by activated CD4+ T cells is not known. Villarino et al. (p. 237
) determined that IL-27R–/–CD4+ T cells activated under nonpolarizing or Th1-polarized conditions expressed higher IL-2 mRNA and secreted more IL-2 protein than wild-type controls. CD4+ T cells from T. gondii-infected IL-27R–/– mice secreted more IL-2 and expressed higher levels of CD25 and FasL at day 14 postinfection compared with wild-type cells. Anti-IL-2 mAb injection at day 7 postinfection increased survival and decreased IFN- serum levels in infected IL-27R–/– mice. The number of IL-2-positive cells was decreased by addition of IL-12 to wild-type or IL-27R–/–CD4+ T cells 48 h after activation under Th1 polarizing conditions; IL-12 plus IL-27 nearly abolished IL-2 production. IL-12 or IL-12 plus IL-27 increased IFN- production from activated CD4+ T cells cultured under nonpolarizing conditions, whereas IL-27 alone had no effect. IL-27, but not IL-12, suppressed IL-2 production by STAT4–/–CD4+ T cells. Proliferation of activated CFSE-labeled IL-27R–/–CD4+ T cells was greater than wild-type cells in nonpolarizing or Th1 polarizing conditions and was partially dependent on IL-2. Both IL-27 and IL-12 induced expression of suppressor of cytokine signaling 3. The experiments demonstrate that IL-27 synergizes with IL-12 to reduce T. gondii-induced inflammation by limiting IL-2 production in activated Th1-polarized CD4+ T cells in mice.
Correcting MRL/lpr lupus
The MRL/lpr mouse strain has a spontaneous mutation in the Fas gene that results in an autoimmune disease similar to human systemic lupus erythematosus. Komori et al. (p. 395
) observed mice in their MRL/lpr breeding colony that exhibited attenuation of systemic lupus erythematosus. They designated the new mutant strain rpl (regression of phenotype associated with lpr) or MRLrpl. Both MRL/lpr and MRLrpl mice lacked Fas expression on thymocytes or spleen cells. However, MRLrpl mice had reduced lymphadenopathy of spleen and lymph nodes, reduced glomerulonephritis and renal vasculitis, decreased blood urea nitrogen, fewer B220+Thy-1+ T cells, and reduced hypergammaglobulinemia and autoantibody production compared with MRL/lpr mice. The lymph node phenotype was mapped to a single locus on the X chromosome by linkage analysis in (MRLrpl x C3H/lpr)F2 mice. A single nucleotide insertion was detected at codon 21 in mRNA for the small adaptor protein signaling lymphocyte-activation molecule-associated protein (SAP). RFLP on genomic DNA mapped the insertion to the first SAP exon. No SAP was detected in thymocyte protein extracts by immunoblotting. The data indicate that SAP is critical in mediating autoimmunity, possibly through activation of Fyn tyrosine kinase, the sole src-family member to interact with it.
Preventing bone loss
Bone remodeling balances osteoclast generation from monocyte/macrophages (by receptor activator of NF-
B ligand (RANKL) and M-CSF produced by osteoblasts) with inhibition of osteoclast formation (by osteoprotegerin (OPG), which blocks binding of RANKL to RANK). IL-1 shifts the balance to bone resorption by increasing production of PGE2 and the ratio of RANKL/OPG in osteoblasts and stromal cells. Ha et al. (p. 111
) found that -lipoic acid (LA) and its reduced form, dihyrolipoic acid (DHLA), inhibited IL-1-induced osteoclast formation in cocultures of mouse primary osteoblasts and bone marrow cells but not in bone marrow macrophage cultures. LA and DHLA inhibited IL-1-induced RANKL mRNA expression and slightly attenuated IL-1-induced reduction of OPG mRNA at 72 h. LA also inhibited vitamin D-induced osteoclast formation or IL-1-induced PGE2 production in cocultures. Addition of RANKL or PGE2 to IL-1-treated cocultures reversed these effects of LA and DHLA. A specific inhibitor of cyclooxygenase-2 (COX-2) blocked IL-1-induced osteoblast generation, inhibited RANKL expression, and prevented down-regulation of OPG mRNA at 72 h in cocultures. DHLA inhibited COX-2 activity in vitro. Daily injection of LA into mice prevented the increased osteoclast numbers and bone resorption of calvarial bones at sites of IL-1-impregnated collagen sponges and the loss of cancellous bone in mice injected with LPS. This study shows that LA prevented IL-1-induced osteoclast differentiation by inhibiting RANKL expression, COX-2 activity, and PGE2 production.
Summaries written by Dorothy L. Buchhagen, Ph.D.
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