ApoB-specific CD4+ T cells circulate in human blood and formation of a memory population is driven by coronary artery disease and an elevated cardiovascular risk profile
Authors: Hansen S , Abogunloko T , Horstmann H , Marchini T , Heitlinger S , Mwinyella T , Gissler M C , Westermann D , Wolf D 
Published: November 2023

Abstract

Aim
Atherosclerosis is a chronic inflammatory disease involving an autoimmune response against Apolioprotein B (ApoB), the core protein of low-density lipoprotein (LDL) cholesterol. Using a translational bench-to-bedside approach, we linked the presence and immuno-phenotype of ApoB-specific CD4+ T cells to clinical risk profiles for cardiovascular disease in humans.

Methods
Peripheral blood mononuclear cells (PBMCs) from 230 patients that underwent coronary angiography were co-incubated in vitro with a pool of immunodominant peptides from human ApoB for 6h. Reactive ApoB-specific T cells (ApoB+) were defined in flow cytometry by expression of the activation marker CD40L. Partition of ApoBpos into naïve and memory T cells was achieved by extracellular fluorochrome-based staining of CD45RO, CCR7 and CD45RA. Cytokine expression of ApoBpos was determined by intracellular staining.

Results
We found that a median of 0.69±0.1% of circulating CD4+ T cells were reactive to Apolipoprotein B. We found detectable concentrations of auto reactive ApoB+ T cells in 86,44% of all healthy individuals. However, overall frequencies of ApoB reactive T cells did not correlate with diagnosed coronary artery disease (CAD). Compared to ApoBneg. T cells, we detected a higher fraction of memory T cells in ApoBpos (p&lt;0,0001), suggesting a previously occurred ApoB directed immune response. Accordingly, elevated serum levels of ApoB specific IgG Antibodies associated with high proportions of ApoB specific memory cells. Patients diagnosed with coronary artery disease presented higher percentages of central memory T cells among ApoBpos compared to healthy individuals. Correspondingly, these observations applied to patients with an elevated 10-year risk for cardiovascular events estimated by the ESC-SCORE2. These effects largely grounded on strong associations with the clinical diagnosis of arterial hypertension, elevated levels of Lp(a) and obesity. Interestingly, systolic blood pressure and LDL-serum levels correlated with elevated proportions of memory-status ApoBpos T cells in patients without statin intake, although this was not the case for patients with LDL-lowering medication. Analysis of cytokine expression in ApoBpos CD4+ T cells showed significantly increased expression of anti-inflammatory Il-2 and IL-10 in addition to pro-inflammatory IFNγ. Cytokine secretion was mainly driven by memory-status ApoBpos when compared to naïve ApoBpos T cells. Interestingly, a significant number of patients showed a mixed TH1/Treg phenotype among ApoBpos with simultaneous expression of IL-10 and IFN-γ.

Conclusions
Our data show for the first time that ApoB-reactive T cells exist even in healthy individuals. Cardiovascular risk factors and clinically relevant atherosclerotic disease drive memory formation and activation of ApoB+ T cells. ApoB+ Memory T cells are prone to secrete pro- and anti-inflammatory cytokines and may modulate systemic inflammation in atherosclerosis.