The Lymphocytic Infiltration in Calcific Aortic Stenosis Predominantly Consists of Clonally Expanded T Cells

Abstract

Valve lesions in degenerative calcific aortic stenosis (CAS), a disorder affecting 3% of those older than 75 years, are infiltrated by T lymphocytes. We sought to determine whether the ␣␤ TCR repertoire of these valve-infiltrating lymphocytes exhibited features either of a polyclonal nonselective response to inflammation or contained expanded clones suggesting a more specific immune process. TCR ␤-chain CDR3-length distribution analysis using PCR primers specific for 23 V␤ families performed in eight individuals with CAS affecting tri-or bileaflet aortic valves revealed considerable oligoclonal T cell expansion. In five cases, ␤-chain nucleotide sequencing in five selected V␤ families showed that an average of 92% of the valve-infiltrating T cell repertoire consisted of expanded T cell clones, differing markedly in composition from the relatively more polyclonal peripheral CD8 or CD4 T cell subsets found even in this elderly population. Twenty-four of the valveinfiltrating T cell clones also had the same clone identified in blood, some of which were highly expanded. Interestingly, 22 of these 24 shared clones were CD8 in lineage (p ‫؍‬ 1.5 ؋ 10 ؊12 ), suggesting a possible relationship to the expanded CD8 ؉ CD28 ؊ T cell clones frequently present in the elderly. Additionally, the sequences of several TCR ␤-chain CDR3 regions were homologous to TCR ␤-chains identified previously in allograft arteriosclerosis. We infer that these findings are inconsistent with a nonselective secondary response of T cells to inflammation and instead suggest that clonally expanded ␣␤ T cells are implicated in mediating a component of the valvular injury responsible for CAS.

The Inflammatory Infiltrate in Calcific Aortic Stenosis is Characterized by Clonal Expansions of T Cells and is Associated with Elevated Proportions of Circulating Activated and Effector Memory CD8 T Cells

“…Since a few clones exhibited sequence homologies to clones previously identified in various inflammatory sites, such as multiple sclerosis lesions and HTLV-1 infection, (Wu et al 2007), this suggests that a minority of CAS clones may be considered as bystander clones (McNally & Welsh 2002) related to the non antigen specific component of inflammation. However, the minor proportion of polyclonal, non-expanded T cells in many CAS samples compared to other inflammatory sites such as atherosclerotic plaques of inflamed synovia (Curran et al 2004, Oksenberg et al 1997, Stemme et al 1991, Swanson et al 1994, argues that inflammation-mediated T cell recruitment is not a general feature of CAS.…”

“…The TCR-chain CDR3 length distribution in valves removed at surgery was found to be highly restricted, with skewed length spectra indicating the presence of a considerable number of oligoclonal expansions, (Wu et al 2007) as illustrated below in Figure 2. Despite considerable heterogeneity, the majority of the infiltrating T cells in most valves and in most BV families consist of oligoclonal expansions, as shown by patterns containing one, two, or three peaks similar to those illustrated.…”

“…The size of each group reflects the extent of clonal expansion and predominance as measured by the frequency distribution of the TCR -chains from each clone, figure 1. For technical details of this methodology, see (Wu et al 2007). Since the molecular events underlying the recombination of V, D, and J segments involve exonuclease nibbling from the ends of the joining segments, as well as the incorporation of additional non-germline nucleotides, the overall length of the -chain is usually randomly altered by some dozens of nucleotides.…”

“…Immunostaining of the valves was performed to define the phenotype and distribution of infiltrating T cells to aid in the interpretation of the repertoire analyses and relating the www.intechopen.com findings in the valve T cell infiltration to the phenotype found in blood , Wu et al 2007). The valve illustrated in figure 4 had a moderate level of polyclonality found by repertoire analysis, however upon staining, the large proportion of the infiltrating T cells exhibit the phenotype CD8 + CD28 -in the region of neovascularization.…”

“…These two primary scenarios can readily be distinguished by TCR repertoire analysis, which can delineate the clonal composition of the T cell infiltrate in the valve leaflet through structural features of the clonally specific -chain T cell TCR. This would help determine whether the inflammatory infiltrate in the valve leaflet was primarily polyclonal, suggesting it was a secondary response to injury, or whether the infiltrate contained expanded T cell clones that would imply features of an adaptive immune response occurring within the valve leaflets (Wu et al 2007). …”