Cardiovascular risk factors: The effects of ageing and smoking on the immune system, an observational clinical study

Currently immunomodulatory compounds are under investigation for use in patients with cardiovascular disease, caused by atherosclerosis. These trials, using recurrent cardiovascular events as endpoint, require enrollment of large patient groups. We investigated the effect of key risk factors for atherosclerosis development, ageing and smoking, on the immune system, with the objective to identify biomarkers differentiating between human populations, and potentially serving as endpoints for future phase 1B trials with immunomodulatory compounds. Blood was collected from young healthy volunteers (aged 18-25 years, n=30), young smokers (18-25 years, n=20), elderly healthy volunteers (>60 years, n=20), heavy smokers (>45 years, 15 packyears, n=11) and patients with stable coronary artery disease (CAD) (>60 years, n=27). Circulating immune cell subsets were characterized by flow cytometry, and collected plasma was evaluated by proteomics (Olink). Clear ageing effects were observed, mostly illustrated by a lower level in CD8⁺ and naïve CD4⁺ and CD8⁺ T cells, with an increase in CD4⁺ and CD8⁺ effector memory T cells in elderly healthy volunteers compared to young healthy volunteers. Heavy smokers showed a more inflammatory cellular phenotype, especially a shift in Th1/Th2 ratio: higher Th1 and lower Th2 percentages compared to young healthy volunteers. A significant decrease in circulating atheroprotective oxLDL-specific IgM was found in patients with CAD compared to young healthy volunteers. Elevated pro-inflammatory and chemotactic proteins TREM1 and CCL11 were observed in elderly volunteers compared to young volunteers. In addition, heavy smokers had an increase in pro-inflammatory cytokine IL-6 and lysosomal protein LAMP3. These data show that ageing and smoking are associated with an inflammatory immunophenotype, and that heavy smokers or aged individuals may serve as potential populations for future clinical trials investigating immunomodulatory drugs targeted for cardiovascular disease.

B cell depletion skews cd4+ t cell towards a pro-inflammatory phenotype in aged atherosclerotic mice

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Dutch Heart Foundation

ERA CVD

Aims

Aging is associated with changes in the composition and function of the immune system, such as decreased B cell numbers and reduced antibody responses (1). In addition, aging is related to an increased incidence of inflammatory diseases, such as the lipid-driven chronic inflammatory disease atherosclerosis, the main underlying cause of cardiovascular disease (2). B cells play a major role in atherosclerosis progression by antibody secretion, antigen presentation and T cell regulation. Different B cell subsets, with either proatherogenic or antiatherogenic properties, have been identified in atherosclerosis, but the impact of aging on B cells during atherosclerosis remains to be elucidated. In contrast to young atherosclerotic mice where few B cells are found within the plaque, single cell RNA sequencing and flow cytometry data from our group revealed that B cells are one of the most dominant leukocytes present in atherosclerotic aortas from naturally aged LDLr-/- mice. In this study, we aimed to gain further insights into the role of these aged B cells on T cell immunity in atherosclerosis by depleting B cells in aged atherosclerotic mice.

Methods and Results

Aged (85-95 weeks) atherosclerotic male LDLr-/- mice were kept on a chow diet for six weeks, during which the mice received 250 µg B cell-depleting anti-CD20 antibody (Genentech) (n=12) or 250 µg rat IgG2a isotype control (n=12) once a week intraperitoneally. Mice that received the anti-CD20 antibody showed effective B cell depletion in the blood and lymphoid organs, such as the spleen and lymph nodes, but also locally in the atherosclerotic plaque. In addition, B cell depleted mice showed a significant increase in the percentage of T-bet expressing CD4+ T cells in aortic plaques compared to control mice (αCD20: 25.05±2.88% vs. ctrl: 15.94±2.14%, p<0.05). Furthermore, the percentage of RORyt+ and IL-17+ CD4+ T cells in the spleen and heart draining lymph nodes was increased after B cell depletion, indicating a shift towards Th17 differentiation.

Conclusions

Collectively, we show that CD20+ B cell depletion in aged LDLr-/- mice skews CD4+ T cells towards a Th1 phenotype in the atherosclerotic plaque and towards a Th17 phenotype in lymphoid organs, suggesting a protective role for aged B cells in atherosclerosis. However, B cells are a heterogeneous population and further research should elucidate whether aged B cells exert a pro- or anti-atherogenic role. In conclusion, our results indicate that aged B cells have an important function in CD4+ T cell differentiation and could be attractive targets to combat age-related cardiovascular disease.

Granzyme B+ CD4+ T cells associate with an unstable plaque phenotype in advanced human atherosclerosis

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): The Dutch Heart Foundation

Cytotoxic CD4+ T cells have previously been found in peripheral blood of patients with coronary artery disease (1), however their occurrence in atherosclerotic plaques and their association with the pathophysiology of atherosclerosis has not been established.

Single-cell RNA sequencing was performed on human carotid atherosclerotic plaques of 18 patients to identify specific T cell populations (2). Next, human femoral and carotid atherosclerotic plaques (n=95) and matched blood samples (n=49) were analyzed by flow cytometry for the presence of CD4+GZMB+ T cells. Plaque morphology was assessed by Movat’s Pentachrome staining.

A distinct cytotoxic GZMB+ PRF1+ CD28- CD4+ T cell cluster was identified using single-cell RNA sequencing. Furthermore, flow cytometry analysis showed that the percentage of GZMB+CD4+ T cells was significantly elevated in plaque compared to blood (Blood: 12.17±2.0 vs. Plaque: 17.40±1.0; P=0.0002). Moreover, a significant positive correlation was observed between the percentage of GZMB+CD4+ T cells in blood versus plaque (P=0.031). In line with the proinflammatory character of these cells, we found a positive association of GZMB+CD4+ T cells (P=0.036) with necrotic core size, whereas no correlation was found with this subtype in the circulation.

In this study we have shown an enrichment of cytotoxic CD4+ T cells in atherosclerotic lesions, which positively correlate with necrotic core size. Future studies are aimed at elucidating the role of these cells in advanced atherosclerosis.

New mutations in two Dutch patients with early infantile galactosialidosis

Galactosialidosis is an autosomal recessive lysosomal storage disease caused by a combined deficiency of lysosomal beta-galactosidase and neuraminidase as a result of a primary defect in the protective protein/cathepsin A (PPCA). We report the first 2 Dutch cases of early infantile galactosialidosis, both presenting with neonatal ascites. The defect was identified in urine, leukocytes, and fibroblasts. Residual activity was determined with a modified assay for cathepsin A and was <5% in leukocytes and <1% in fibroblasts. Histological examination of the placenta in case 1 showed extensive vacuolization in all cell types. Northern blot analysis of RNA isolated from the patients' cultured fibroblasts showed substantially decreased levels of the PPCA transcript, which nevertheless had the correct size of 2 kb. Mutation analysis of both mRNA and genomic DNA from the patients identified two novel mutations in the PPCA locus. Case 1 was a compound heterozygote, with a single missense mutation in one allele, which resulted in Gly57Ser amino acid substitution, and a single C insertion at nucleotide position 899 in the second allele, which gave rise to a frame shift and premature termination codon. Case 2 was homozygous for the same C899 insertion found in case 1.

Efficient replication of human immunodeficiency virus type 1 and measles virus in a human-to-mouse graft versus host disease model permits immunization research

An acute graft versus host disease (GvHD) murine model was developed to study the pathogenic and protective mechanisms against viruses that replicate in cells of the human immune system. The model allowed efficient replication of lymphotropic, macrophage and amphitropic strains of human immunodeficiency virus type 1 (HIV-1) and measles virus (MV). Cytopathic lymphotropic strains of HIV-1 and a wild-type MV strain replicated in a 'burst'-like manner, whereas a non-cytopathic lymphotropic HIV-1 strain and all macrophage-tropic HIV-1 strains caused persistent infection of the graft. The replication kinetics of infection with these viruses were highly reproducible and were very similar to those observed in natural infection of humans. Infection with these viruses, with the exception of HIV-1SF2, led to a delay [corrected] and abrogation of the GvHD, indicating a direct immunosuppressive effect. Interestingly, infection with the lymphotropic HIV-1SF2 strain was rapidly and spontaneously abrogated. The model was also shown to be suitable for the evaluation of passive immunization strategies. Administration of a combination of antibodies against the HIV-1 V3 loop and the HIV-1 CD4 binding sites prevented subsequent infection with HIV-1IIIB. In contrast, administration of CD4 binding site specific human monoclonal antibody at a concentration that would neutralize the virus in vitro enhanced in vivo infection with HIV-1IIIB. The model also allowed evaluation of in vivo immunization studies. Immunization with a live attenuated measles vaccine resulted in protection from a wild-type MV challenge, whereas immunization with a subunit candidate vaccine appeared to give partial protection.

In vitro suppression of leukemia by alkylated interleukin-3

We report the in vitro suppression of the IL-3-dependent MO-7 acute myeloid leukemia proliferation by an interleukin-3 antagonist. The antagonist was generated by alkylation to inactivate catalytic His-residues of native human interleukin-3. The resulting inhibitor caused a factor 7 inhibition of the growth-response curve of the IL-3 control-stimulated proliferation of a MO-7 leukemia cell line. A 40% inhibition of the MO-7 proliferation could be achieved with a partially alkylated inhibitor in presence of a factor 30 excess of native IL-3. Therefore, the inhibitor had a substantially improved affinity for the IL-3 receptor on these leukemia cells. At a concentration of as low as 0.1 ng/ml it still caused a 2-fold inhibition of the native IL-3-stimulated proliferation response curve. Thus it can be concluded that this alkylate IL-3 is a potent IL-3 antagonist. Based on the reported specific zinc binding of IL-2, IL-6, GM-CSF and gamma-interferon this suggests that more leukemias and even other forms of cancer can be effectively suppressed by alkylated growth factors.

Native electrophoresis to monitor chemical modifications of human interleukin-3

Native electrophoresis on the Pharmacia PhastSystem using a new buffer system is used to monitor chemical modifications of human interleukin-3. The method is faster, more gentle and more convenient than amino acid analysis. Micrograms of protein suffice in contrast with milligrams required in spectrophotometric methods. As compared to generally used native electrophoresis, the combination of a changed conductivity, lower pH and the low density matrix results in a much better separation and detection of both the reaction products containing a high charge and the reaction products containing a low charge. This enables monitoring of extensive modifications as well as mild modifications. Our method also provides indications for denaturation of the protein. It has proven to be highly reproducible for at least 10 different modification reactions. Information can be obtained about the presence of the various distinct forms of the modified molecule, for instance leading to the average number of groups on the molecule. It also detects modifications not detectable with generally used native electrophoresis.

Human interleukin-3 contains a discontinuous zinc binding domain

The primary structure of human interleukin-3 contains two amino acid consensus sequences at Glutamate 22- Histidine 26 and Histidine 95-Histidine 98, that are characteristic for zinc binding proteins. Therefore, the hypothesis was tested that human interleukin-3 binds zinc specifically by either one or both sequences. Protein dotblotting, followed by probing with radioactive zinc demonstrated specific zinc binding of interleukin-3. Metal specificity was confirmed by competition experiments with 12 other divalent- and trivalent metal ions. Protease treatment combined with plasma desorption mass spectrometry was used to localize the zinc binding domain. Specific zinc binding was restricted to a fragment composed of Threonine 11-Lysine 28 and Asparagine 80-Lysine 100. It was found to decrease by a factor of five when either of these two amino acid stretches was missing. It is concluded that human interleukin-3 is a zinc binding protein. Interleukin-3 zinc binding capacity is largely determined by both moieties of the protein that contain the consensus sequences. In addition we propose that the zinc binding of hIL-3 is involved in (de)phosphorylation of the hIL-3 receptor.

Detection of migrated allogeneic oligodendrocytes throughout the central nervous system of the galactocerebrosidase-deficient twitcher mouse

Galactocerebrosidase-deficient oligodendrocytes of 'twitcher' (twi/twi) mice degenerate prematurely. Transplantation of normal bone marrow cells has been shown to alleviate symptoms and to prolong survival time. However, characteristic ataxia ('twitching') is not cured. In an attempt to improve further the condition of twitcher mice, allogeneic foetal liver cells were transplanted as a source of normal haemopoietic stem cells and supplemented with intracerebral transplantation of foetal brain cells. A reliable method was developed to detect donor-type cells in brain tissue. Bacteriophage lambda transgenic foetal mice were used as donors of both foetal liver and brain cells. Integrated copies of lambda DNA in donor cells were detected by in situ hybridization with biotinylated probes, which were then stained using streptavidin alkaline phosphatase. This technique was combined with immunohistochemistry to distinguish donor-type oligodendrocytes from macrophages. Immunoperoxidase staining with an antiserum to carbonic anhydrase-II produced dark perikarya of oligodendrocytes. The results demonstrated that local foetal brain cell grafts resulted in a wide dissemination of donor-type oligodendrocytes throughout the twitcher brain. The addition of a foetal brain cell graft to haemopoietic cell transplantation resulted in significantly prolonged survival of twitcher mice.