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

Abstract

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.

Phenotype and Effector Function of CC Chemokine Receptor 9-Expressing Lymphocytes in Small Intestinal Crohn’s Disease

“…These data suggest the potential involvement of CCR9 ϩ T cells in the pathogenesis of SB CD (11). Furthermore, we have demonstrated that the memory subset of circulating CCR9 ϩ CD4 ϩ T cells in healthy donors has characteristics of mucosal T lymphocytes since they have an activated phenotype, respond to anti-CD2 stimulation, and exhibit a Th1 or T regulatory 1 cytokine profiles (12).…”

“…The combined expression of ␣ 4 ␤ 7 /CCR9 by intestinal homing T lymphocytes may further define SB vs colonic mucosal T cell trafficking through CCL25 (selectively expressed in the SB) triggering of integrin activation from CCR9 engagement (9,10). Therefore, expression of CCR9 by mucosal homing T cells may be used to distinguish SB from colonic immune responses (12). CCL25 is selectively expressed in the thymus and SB endothelial cells, intestinal crypts, and a subset of LP cells (9,10).…”

“…IFN-␥ was quantitated in culture supernatants by amplified sandwich ELISA as reported previously (12). Briefly, 96-well microtiter plates were coated overnight with anti-IFN-␥ mAb (BD Pharmingen).…”

“…Chemokines constitute a large family of small (ϳ8 -14 kDa), structurally related heparin binding proteins, which are constitutively expressed in lymphoid and extra lymphoid tissues, and play a critical role in immune homeostasis by regulating lymphocyte trafficking to or within lymphoid organs and in peripheral tissues (7)(8)(9)(10)(11)(12)(13). They are classified as C, CC, CXC, and CX3C based on the positioning of cysteine residues that form two disulfide bonds (14).…”

“…The only known receptor for CCL25, CCR9, is highly expressed on developing thymocytes and small intestinal lamina propria lymphocytes (LPL) and intraepithelial lymphocytes (9,10,16). We and others (9,10,12) have proposed that the CCL25/CCR9 chemokine ligand receptor pair may play an important role in the regional specialization of intestinal immunity and that the coexpression of CCR9 and ␣ 4 ␤ 7 on the cell surface may provide a small intestinal "address code" for circulating intestinal memory T cells. We previously reported, that in peripheral blood (PB), CCR9 ϩ T lymphocytes were markedly elevated in patients with SB immune-mediated diseases, including CD, but not in patients with purely colonic CD, and that CCL25 expression is altered in inflamed SB but is not expressed in either normal or inflamed colon.…”