Host-Derived Smooth Muscle Cells Accumulate in Cardiac Allografts: Role of Inflammation and Monocyte Chemoattractant Protein 1

Transplant arteriosclerosis is characterized by inflammation and intimal thickening caused by accumulation of smooth muscle cells (SMCs) both from donor and recipient. We assessed the relationship between clinical factors and the presence of host-derived SMCs in 124 myocardial biopsies from 26 consecutive patients who received hearts from opposite-sex donors. Clinical and demographic information was obtained from the patients' medical records. Host-derived SMCs accounted for 3.35±2.3% of cells in arterioles (range, 0.08–12.51%). As shown by linear regression analysis, an increased number of SMCs was associated with rejection grade (mean, 1.41±1.03, p = 0.034) and the number of leukocytes (19.1±12.7 per 20 high-power fields, p = 0.01). The accumulation of host-derived SMCs was associated with an increased number of leukocytes in the allografts. In vitro, monocyte chemoattractant protein 1 (MCP-1) released from leukocytes was crucial for SMC migration. After heart allotransplantion, mice treated with MCP-1-specific antibodies had significantly fewer host-derived SMCs in the grafts than mice treated with isotypic antibody controls. We conclude that the number of host-derived SMCs in human cardiac allografts is associated with the rejection grade and that MCP-1 may play pivotal role in recruiting host-derived SMCs into cardiac allografts

Logistic linear regression analysis of the association between predicting factors and accumulation of vascular progenitor cells in arterioles.

<p>Logistic linear regression analysis of the association between predicting factors and accumulation of vascular progenitor cells in arterioles.</p

Immnunohistochemical analysis of mouse cardiac allograft treated anti-MCP-1 or isotypic control.

<p>(A and B) Distribution of CD45⁺ leukocytes in cardiac allografts treated with anti-MCP-1 antibodies (A) and control isotypic antibodies (B). (C and D) Distribution of CD68⁺ leukocytes in cardiac allografts treated with antibodies against MCP-1 antibodies (C) and control isotypic antibodies (D). Blue, positive signal; red, nuclear counterstaining. (E) Numbers of αSMA-positive vessels and leukocytes expressing CD45, CD68, CD3, CD4, and CD8. *p<0.05.</p

Baseline characteristic of the patients^*.

*<p>Values are numbers of patients, unless indicated otherwise.</p

Migration of SMCs <i>in vitro</i>.

<p>SMC migration was induced by leukocyte-conditioned medium and MCP-1 and inhibited by neutralizing antibodies against MCP-1 and CCR2. *p<0.05.</p

Logistic linear regression analysis of factors associated with accumulation of vascular progenitor cells in arterioles.

<p>HDL, high density lipoprotein; LDL, low density lipoprotein.</p

Staining of mouse cardiac allografts for αSMA to identify the origin of cells expressing αSMA.

<p>(A and B) Host-derived SMCs were present in arterioles with a single layer of SMCs (yellow) (A) but not in those with more SMC layers (B). Arrows indicate host-derived cells. Blue, αSMA; green, green fluorescent protein; red, nuclear counterstaining. Confocal microscopy analysis is followed by hematoxylin-eosin staining of parallel sections in order to present structure of vessels. Staining of human cardiac allografts for MCP-1 revealed MCP-1 around the small arterioles in an area with inflammation (C).</p

Immunohistochemical characteristic of human cardiac allografts.

<p>(A) Immunohistochemistry for αSMA (blue) followed by in situ hybridization for chromosome Y (green) and nuclear counterstaining (red). (B–K) Immunohistochemical staining of human cardiac allografts for αSMA (B), vWF (C), CD45 (D), CD14 (E), IgG (F), IgM (G), CD4 (H), and CD8 (I). Arrows indicate positive cells and staining. (J and K) Scatter plots showing the association between the number of αSMA-positive cells in the vessel and patient age (J) CD45+ cells (K).</p