A butyrophilin family member critically inhibits T cell activation

The costimulatory molecules in the B7-CD28 families are important in the regulation of T cell activation and tolerance. The butyrophilin family of proteins shares sequence and structure homology with B7 family molecules; however, the function of the butyrophilin family in the immune system has not been defined. In this study, we performed an analysis on multiple butyrophilin molecules and found that butyrophilin-like (BTNL)1 molecule functions to dampen T cell activation. BTNL1 mRNA was broadly expressed, but its protein was only found in APCs and not T cells. The putative receptor for BTNL1 was found on activated T cells and APCs. Also, recombinant BTNL1 molecule inhibited T cell proliferation by arresting cell cycle progression. The administration of neutralizing Abs against BTNL1 provoked enhanced T cell activation and exacerbated disease in autoimmune and asthma mouse models. Therefore, BTNL1 is a critical inhibitory molecule for T cell activation and immune diseases.

Statins induce regulatory T cell recruitment via a CCL1 dependent pathway

The statins, a group of inhibitors of the 3-hydroxy-3-methylglutaryl coenzyme A reductase, are reported to influence a variety of immune system activities through 3-hydroxy-3-methylglutaryl coenzyme A reductase-dependent and -independent mechanisms. How statin treatment regulates immune system function in vivo nonetheless remains to be fully defined. We analyzed the immunomodulatory effects of lovastatin in a Candida albicans-induced delayed-type hypersensitivity reaction in mice. In this model, lovastatin administration reduced the acute inflammatory response elicited by C. albicans challenge. This anti-inflammatory activity of lovastatin was associated with a shift from a Th1 to a Th2 immune response, as well as an increase in the percentage of regulatory T cells at the inflammation site and in the regional draining lymph node. The lovastatin-induced increase in regulatory T cells in the inflamed skin was dependent on expression of CCL1, a chemokine that is locally up-regulated by statin administration. The anti-inflammatory effect of lovastatin was abrogated in CCL1-deficient mice. These results suggest that local regulation of chemokine expression may be an important process in statin-induced modulation of the immune system.

Coordinated involvement of mast cells and T cells in allergic mucosal inflammation: critical role of the CC chemokine ligand 1:CCR8 axis

CCL1 is the predominant chemokine secreted from IgE-activated human and mouse mast cells in vitro, colocalizes to mast cells in lung biopsies, and is elevated in asthmatic airways. CCR8, the receptor for CCL1, is expressed by approximately 70% of CD4(+) T lymphocytes recruited to the asthmatic airways, and the number of CCR8-expressing cells is increased 3-fold in the airways of asthmatic subjects compared with normal volunteers. In vivo, CCL1 expression in the lung is reduced in mast cell-deficient mice after aeroallergen provocation. Neutralization of CCL1 or CCR8 deficiency results in reduced mucosal lung inflammation, airway hyperresponsiveness, and mucus hypersecretion to a similar degree as detected in mast cell-deficient mice. Adenoviral delivery of CCL1 to the lungs of mast cell-deficient mice restores airway hyperresponsiveness, lung inflammation, and mucus hypersecretion to the degree observed in wild-type mice. The consequences of CCR8 deficiency, including a marked reduction in Th2 cytokine levels, are comparable with those observed by depletion of CD4(+) T lymphocytes. Thus, mast cell-derived CCL1- and CCR8-expressing CD4(+) effector T lymphocytes play an essential role in orchestrating lung mucosal inflammatory responses.

Analysis of post-translational CCR8 modifications and their influence on receptor activity

Post-translational modifications of the extracellular portions of receptors located in the cell membrane can contribute to modulating their biological activity. Using a mutagenesis approach in which single or multiple Tyr-to-Phe, Thr-to-Ala, Ser-to-Ala, and Asn-to-Gln substitutions were made at the appropriate positions, we analyzed the sulfation and glycosylation state of the murine CCR8 chemokine receptor, and the way in which these post-translational modifications affect CCR8 activity. A Y14Y15-to-F14F15 CCR8 mutant was less sulfated than the wild-type receptor. An N8-to-Q8 mutant was less glycosylated than wild-type, and a double T10T12-to-A10A12 mutant showed even less glycosylation. We established a flow cytometric analysis with an Fc-fused form of mouse CCL1 to determine precisely the ligand-binding activity of these mutants. Single mutants at amino acid positions 8, 10 or 12 bound CCL1-Fc similarly to wild-type CCR8, whereas the F14F15 double mutant was essentially inactive and the A10A12 double mutant showed about 65% of wild-type ligand-binding activity. Calcium flux activity assays were performed with these mutants, yielding results consistent with those from the ligand binding assays. These data indicate that sulfation at specific positions of the N-terminal domain of mouse CCR8 is critical for its biological activity, whereas glycosylation has a minor influence.

Absence of CCR8 does not impair the response to ovalbumin-induced allergic airway disease

Interaction of chemokines with their specific receptors results in tight control of leukocyte migration and positioning. CCR8 is a chemokine receptor expressed mainly in CD4(+) single-positive thymocytes and Th2 cells. We generated CCR8-deficient mice (CCR8(-/-)) to study the in vivo role of this receptor, and describe in this study the CCR8(-/-) mouse response in OVA-induced allergic airway disease using several models, including an adoptive transfer model and receptor-blocking experiments. All CCR8(-/-) mice developed a pathological response similar to that of wild-type animals with respect to bronchoalveolar lavage cell composition, peripheral blood and bone marrow eosinophilia, lung infiltrates, and Th2 cytokine levels in lung and serum. The results contrast with a recent report using one of the OVA-induced asthma models studied here. Similar immune responses were also observed in CCR8(-/-) and wild-type animals in a different model of ragweed allergen-induced peritoneal eosinophilic inflammation, with an equivalent number of eosinophils and analogous increased levels of Th2 cytokines in peritoneum and peripheral blood. Our results show that allergic diseases course without critical CCR8 participation, and suggest that further work is needed to unravel the in vivo role of CCR8 in Th2-mediated pathologies.

The transient expression of C-C chemokine receptor 8 in thymus identifies a thymocyte subset committed to become CD4+ single-positive T cells

Developing T cells journey through the different thymic microenvironments while receiving signals that eventually will allow some of them to become mature naive T cells exported to the periphery. This maturation can be visualized by the phenotype of the developing cells. CCR8 is a ss-chemokine receptor preferentially expressed in the thymus. We have developed 8F4, an anti-mouse CCR8 mAb that is able to neutralize the ligand-induced activation of CCR8, and used it to characterize the CCR8 protein expression in the different thymocyte subsets. Taking into account the intrathymic lineage relationships, our data showed that CCR8 expression in thymus followed two transient waves along T cell maturation. The first one took place in CD4(-) CD8(-) double-negative thymocytes, which showed a low CCR8 expression, and the second wave occurred after TCR activation by the Ag-dependent positive selection in CD4(+) CD8(+) double-positive cells. From that maturation stage, CCR8 expression gradually increased as the CD4(+) cell differentiation proceeded, reaching a maximum at the CD4(+) CD8(-) single-positive stage. These CD4(+) cells expressing CCR8 were also CD69(high) CD62L(low) thymocytes, suggesting that they still needed to undergo some differentiation step before becoming functionally competent naive T cells ready to be exported from the thymus. Interestingly, no significant amounts of CCR8 protein were detectable in CD4(-) CD8(+) thymocytes. Our data showing a clear regulation of the CCR8 protein in thymus suggest a relevant role for CCR8 in this lymphoid organ, and identify CCR8 as a possible marker of thymocyte subsets recently committed to the CD4(+) lineage.

Down-regulation of the beta-chemokine receptor CCR6 in dendritic cells mediated by TNF-alpha and IL-4

Chemokines are involved in the control of dendritic cell (DC) trafficking, which is critical for the immune response. We have generated DC from human umbilical cord blood CD34+ progenitors cultured with granulocyte-macrophage colony-stimulating factor, tumor necrosis factor alpha (TNF-alpha), and stem cell factor. Using an anti-CCR6 monoclonal antibody, we observed that these cells showed maximum expression of this beta-chemokine receptor when they were immature, as determined by their relatively low expression of several DC maturation markers such as CD1a, CD11c, CD14, CD40, CD80, and CD83. Immature DC responded strongly to macrophage inflammatory protein-3alpha (MIP-3alpha), the CCR6 ligand, in migration and calcium mobilization assays. CCR6 expression decreased in parallel with the DC maturation induced by prolonged TNF-alphaq treatments. Interleukin-4 was also able to decrease CCR6 protein levels. Our findings suggest that the MIP-3alpha/CCR6 interaction plays an important role in the trafficking of immature DC to chemokine production sites such as injured or inflamed peripheral tissues, where DC undergo maturation on contact with antigens.

Identification of CCR8 as the specific receptor for the human beta-chemokine I-309: cloning and molecular characterization of murine CCR8 as the receptor for TCA-3

Chemokine receptor-like 1 (CKR-L1) was described recently as a putative seven-transmembrane human receptor with many of the structural features of chemokine receptors. To identify the ligand of CKR-L1, we have studied chemokine-induced calcium mobilization in 293 cells transfected with CKR-L1. Of 20 different chemokines tested, only I-309 was able to elicit a significant calcium mobilization. In addition, I-309 induced the transfectants to migrate in vitro. As expected for chemokine receptor-mediated effects, pertussis toxin, but not cholera toxin, inhibited both the calcium flux and migration of the CKR-L1 transfectants in response to I-309. All of these data support the conclusion that I-309 is a functional ligand for CKR-L1. According to the current chemokine receptor nomenclature, we have designated this gene as CCR8. The murine CCR8 (mCCR8) gene was cloned, and its predicted amino acid sequence showed a 71% identity with that of human CCR8. As human CCR8, mCCR8 is expressed in thymus. Both I-309 and its murine homologue TCA-3 were able to induce calcium mobilization in transiently transfected 293-EBNA cells expressing mCCR8. The affinity of the binding of 125I-labeled TCA-3 to mCCR8 was high (Kd approximately 2 nM); the binding was prevented completely by an excess of cold TCA-3, and only partially competed (40%) by I-309. The identification of I-309 and TCA-3 as the functional ligands for CCR8 receptors will help to unravel the role of these proteins in physiologic and pathologic situations.

Association between ocular pressure and certain health parameters

Intraocular pressure (IOP) was measured in a mixed population of 12,803 apparently healthy employed people. Mean IOP was 13.5 +/- 3.3 mmHg, without sex difference. Frequency distribution demonstrated skewness towards high values. IOP weakly correlated with age (R = 0.06), and older subgroups showed more marked skewness, but further analysis showed this effect to be spurious. The correlations of IOP with heart rate and with systolic blood pressure were small, but stronger than with age (R = .16 and .15, respectively). Moreover, when corrected for heart rate, the effect of age was nullified. Other factors found to be correlated with IOP included blood glucose and hemoglobin concentration, smoking, and height. None of these factors significantly increased the correlation between IOP and heart rate or blood pressure, and the skewness was not fully explained by any of these factors or their combinations. The value of the epidemiologic approach to detection of factors responsible for ocular hypertension is stressed.