CXCR6 identifies a putative population of retained human lung T cells characterised by co-expression of activation markers.

Expressions of activation markers have been described on the surface of T cells in the blood and the lung in both health and disease. We have studied the distribution of activation markers on human lung T cells and have found that only certain populations exist. Importantly, the presence or absence of some markers appears to predict those of others, in particular cells which express CD103 also express CD49a and CD69, whereas cells which do not express CD69 also do not express CD49a or CD103. In view of the paucity of activation marker expression in the peripheral blood, we have hypothesised that these CD69+, CD49a+, and CD103+ (triple positive) cells are retained in the lung, possess effector function (IFNgamma secretion) and express particular chemokine receptors which allow them to be maintained in this environment. We have found that the ability of the triple negative cells to secrete IFNgamma is significantly less than the triple positive cells, suggesting that the expression of activation markers can highlight a highly specialised effector cell. We have studied the expression of 14 chemokine receptors and have found that the most striking difference between the triple negative cells and the triple positive cells is the expression of CXCR6 with 12.8+/-9.8% of triple negative cells expressing CXCR6 compared to 89.5+/-5.5% of triple positive cells. We propose therefore that CXCR6 may play an important role in the retention of T cells within the lung.

IL-4-expressing bronchoalveolar T cells from asthmatic and healthy subjects preferentially express CCR 3 and CCR 4.

BACKGROUND: The concept of the polarization of chemokine receptor expression by T(H)1 and T(H)2 cells provides an attractive mechanism for their differential recruitment to tissue, which could be subject to disease-specific therapeutic intervention. The paradigm that T(H)1 cells preferentially express CXCR 3 and CCR 5 and T(H)2 cells preferentially express CCR 3, CCR 4, and CCR 8 has been well established in the setting of in vitro polarized cell lines; however, the situation in vivo appears less clear-cut. OBJECTIVE: We sought to investigate whether this pattern of polarization can be demonstrated in human lung tissue. METHODS: We used single-cell analysis to investigate the relationship between chemokine receptor expression and cytokine production on peripheral blood and bronchoalveolar lavage fluid T cells in patients with asthma, a putative T(H)2 disease, as well as in healthy control subjects. RESULTS: We have found in both asthmatic and control subjects that IL-4-expressing blood and bronchoalveolar lavage fluid T cells are significantly more likely to express the T(H)2 type 2 chemokine receptors CCR 3 and CCR 4, with 10-fold and 2-fold differences in expression, respectively, compared with IFN-gamma-expressing cells. CONCLUSION: We have provided evidence that polarization of T(H)2-type chemokine receptors on IL-4-expressing cells can be demonstrated in an in vivo setting and therefore that these cells might indeed be susceptible to differential patterns of recruitment as a result of expression of the relevant chemokines at inflammatory sites.

Differential expression of CCR3 and CXCR3 by human lung and bone marrow-derived mast cells: implications for tissue mast cell migration.

The selective microlocalization of mast cells within specific airway structures, such as the airway smooth muscle and submucosal glands, in asthma is important in the pathophysiology of inflammatory lung disease. Chemokines are likely candidates mediating mast cell migration into these tissue compartments. In this study, we have defined the chemokine receptor profile of human lung mast cells (HLMC) compared with mast cells derived from human bone marrow (BM) and the human mast cell line HMC-1. CXC chemokine receptor 3 (CXCR3) was the most highly expressed chemokine receptor on ex vivo HLMC analyzed by flow cytometry, and CXCR3 expression by mast cells in the bronchial mucosa was confirmed by immuno-histochemistry. CXCR3 was functional, inducing a rise in cytosolic-free Ca2+, actin reorganization, and chemotaxis in response to the CXC ligands CXCL9, -10, and -11. CXCR3 activation did not induce degranulation or cytokine synthesis. In addition, more than 10% of ex vivo HLMC expressed CC chemokine receptor 3, CXCR1, and CXCR4. It is interesting that CXCR3 was not expressed by human BM-derived mast cells, suggesting its expression is induced during tissue maturation. As CXCR3 ligands are elevated in many pulmonary diseases, CXCR3 may be important for determining the anatomical microlocalization of mast cells within the human lung.