Constitutive homing of mast cell progenitors to the intestine depends on autologous expression of the chemokine receptor CXCR2

Abstract

Homing of mast cell progenitors (MCps) to the mouse small intestine involves the interaction of alpha4beta7 integrin with mucosal addressin cellular adhesion molecule-1 (MAdCAM-1). We now demonstrate the dependence of this process on CXC chemokine receptor 2 (CXCR2) and vascular cell adhesion molecule-1 (VCAM-1) using null strains and mice sublethally irradiated and bone marrow (BM) reconstituted (SIBR) with wild-type or null BM or with wild-type BM followed by administration of blocking antibody. The intestinal MCp concentration in CXCR2(-/-) mice was reduced by 67%, but was unaltered in CC chemokine receptor 2(-/-) (CCR2(-/-)), CCR3(-/-), or CCR5(-/-) mice. SIBR mice given CXCR2(-/-) BM had an intestinal MCp concentration that was 76% less than that in BALB/c BM reconstituted mice. Antibody blockade of VCAM-1 or of CXCR2 in SIBR mice reduced intestinal MCp reconstitution, and mice lacking endothelial VCAM-1 also had a marked reduction relative to wild-type mice. Finally, the half-life of intestinal MCps in wild-type mice was less than one week on the basis of a more than 50% reduction by administration of anti-alpha4beta7 integrin or anti-CXCR2. Thus, the establishment and maintenance of MCps in the small intestine is a dynamic process that requires expression of the alpha4beta7 integrin and the alpha-chemokine receptor CXCR2.

Figure 1.

Selective loss of MCps in the intestine of CXCR2^-/- mice. (A) MCp concentrations in the intestine, lung, spleen, and BM of wild-type BALB/c mice (▪) and CXCR2^-/- mice (□) evaluated in parallel. Concentrations are expressed as MCps per 10⁶ MNCs isolated from the various tissues. Values are the mean ± SEM for 5 separate experiments, except for BM where values are the mean ± ½ range for 2 separate experiments. ^*Statistical significance, with P < .001 relative to BALB/c mice. (B) Absolute numbers of MCps per tissue for the same tissues shown in panel A.

Figure 2.

Reduced intestinal MCps in SIBR BALB/c mice receiving CXCR2^-/- BM. (A) MCp concentrations in the intestine, lung, spleen, and BM in SIBR mice receiving BALB/c BM (▪) and SIBR mice receiving CXCR2^-/- BM (□) evaluated in parallel. Values are the mean ± SEM for 4 separate experiments except BM, where values are the mean ± SEM for 3 separate experiments. ^*Statistical significance, with P < .01 relative to wild-type BM-reconstituted mice. (B) The absolute numbers of MCps per tissue for the same tissues shown in panel A.

Figure 3.

Reduced intestinal MCp reconstitution in SIBR mice by treatment with anti–MAdCAM-1 or anti–VCAM-1 and in VCAM-1^-/- mice. (A-B) Bars represent the intestinal MCp concentrations (A) and the absolute number of intestinal MCps (B) in SIBR mice reconstituted with wild-type BM cells and treated with saline or antibody (Ab) directed against the indicated endothelial ligands. Values are the mean ± SEM for 4 experiments. (C-D) Bars represent the intestinal MCp concentrations (C) and the absolute number of intestinal MCps (D) in VCAM-1Flox and in VCAM^-/- mice evaluated in parallel. Values are the mean ± SEM for 3 experiments.

Figure 4.

Reduced intestinal MCp reservoir in wild-type mice by treatment with anti-α4β7 integrin and anti-CXCR2 antibodies. (A-B) Bars represent the intestinal MCp concentrations (A) and the absolute number of intestinal MCps (B) in mice treated with saline or antibody directed against the indicated integrins. Values are the mean ± SEM for 4 experiments. ^*Statistical significance (P < .05) relative to mice treated with anti-β1 integrin antibody. (C-D) Bars represent the intestinal MCp concentrations (C) and the absolute number of intestinal MCps (D) in mice treated with normal rabbit IgG or antibody directed against the chemokine receptor CXCR2. Values are the mean ± SEM for 3 experiments. ^*Statistical significance (P < .05) relative to mice treated with normal rabbit IgG.