Yet Another Alarming Research Finding! Persistence of SARS CoV-2 S1 Protein Found in CD16+ Monocytes Of Post COVID-19 Patients Up To 15 Months After So-Called Recovery!
: A new research by scientist from California, Massachusetts, New York, Orlando and also Costa Rican researchers have discovered that in patients having being deemed as recovered from COVID-19 but are still suffering from Long COVID conditions, it was found that even 15 months later, there was SARS-CoV-2 S1 protein found in the CD16+ monocytes of these patients. The study has numerous implications that need further studies to verify including the fact that viral persistence is present in recovered COVID-19 patients are concealing themselves in reservoirs (The CD16+ monocytes could even be serving as reservoirs for the virus or its spike proteins) , that the SARS-CoV-2 virus could be directly attacking the intermediate and non-classical monocytes as what many previous studies had even suggested in the past, that the spike protein could also playing a key role in long COVID-19 manifestations.
According to the study abstract, “The recent COVID-19 pandemic is a treatment challenge in the acute infection stage but the recognition of chronic COVID-19 symptoms termed post-acute sequelae SARS-CoV-2
infection (PASC) may affect up to 30% of all infected individuals. The underlying mechanism and source of this distinct immunologic condition three months or more after initial infection remains elusive. The study team investigated the presence of SARS-CoV-2 S1 protein in 46 individuals. The team analyzed T-cell, B-cell, and monocytic subsets in both severe COVID-19 patients and in patients with post-acute sequelae of COVID-19 (PASC). The levels of both intermediate (CD14+, CD16+) and non-classical monocyte (CD14Lo, CD16+) were significantly elevated in PASC patients up to 15 months post-acute infection compared to healthy controls (P=0.002 and P=0.01, respectively). A statistically significant number of non-classical monocytes contained SARS-CoV-2 S1 protein in both severe (P=0.004) and PASC patients (P=0.02) out to 15 months post infection. Non-classical monocytes were sorted from PASC patients using flow cytometric sorting and the SARS-CoV-2 S1 protein was confirmed by mass spectrometry. Cells from 4 out of 11 severe COVID-19 patients and 1 out of 26 also contained SARS-CoV-2 RNA. Non-classical monocytes are capable of causing inflammation throughout the body in response to fractalkine/CX3CL1 and 70 RANTES/CCR5.
The study findings were published on a preprint server and are currently being peer reviewed. https://www.biorxiv.org/content/10.1101/2021.06.25.449905v1
Already Thailand Medical News had suggested through an unproven hypothesis that the SARS-CoV-2 coronavirus was much more dangerous than HIV as it was attacking the various components of the human immune system including the T Cells and was disrupting numerous immune pathways. https://www.thailandmedical.news/news/hypothesis-sars-cov-2-variants-worse-than-hiv,-disrupting-immune-system-and-giving-rise-to-dangerous-opportunistic-infections-including-candida-auris
This new study finding only adds to the list of our concerns.
The three subtypes of circulating monocytes (c
lassical, intermediate, non-classical) express very different cell surface molecules and serve very different functions in the immune system. Generally, classical’ monocytes exhibit phagocytic activity, produce higher levels of ROS and secrete proinflammatory molecules such as IL-6, IL-8, CCL2, CCL3 and CCL5. Intermediate monocytes express the highest levels of CCR5 and are characterized by their antigen presentation capabilities, as well as the secretion of TNF-α, IL-1β, IL-6, and CCL3 upon TLR stimulations. Non-classical monocytes expressing high levels of CX3CR1 are involved in complement and Fc gamma-mediated phagocytosis and anti-viral responses.
Typically after maturation, human monocytes are released from bone marrow into the circulation as classical monocytes. Strong evidence supports the concept that intermediate and nonclassical monocytes emerge sequentially from the pool of classical monocytes. This is supported by transcriptome analysis showing that CD16+ monocytes have a more mature phenotype .
In humans, 85% of the circulating monocyte pool are classical monocytes, whereas the remaining 15% consist of intermediate and nonclassical monocytes. Classical monocytes have a circulating lifespan of approximately one day before they either migrate into tissues, die, or turn into intermediate and subsequently nonclassical monocytes. During pathologic conditions mediated by infectious/inflammatory reactions, the proportions of monocyte subsets vary according to the functionality of each specific subpopulation.
Previous study results show that during early stages of the disease, PASC group have reduced classical monocyte and increased intermediate monocyte percentages compared with healthy controls.
However in this study, the researchers report an increase in nonclassical monocytes in PASC group 6-15 months post infection, and higher percentages of intermediate and nonclassical monocytes at day 0 in severe cases, suggesting augmented classical-intermediate-nonclassical monocyte transition in both groups but with different kinetics. (Note a possible reasoning for this new observations could also be due to the fact that the new variants are behaving differently from the initial strains that were studied.)
The clinical relevance of monocyte activation in COVID-19 patients and the significance of these cells as viral protein reservoir in PASC is supported by the team’s data reporting the presence of S1 protein within nonclassical monocytes. Viral particles and/or viral proteins can enter monocyte subpopulations in distinct ways, and this appears to be regulated differently in individuals that will develop severe disease or PASC.
Classical monocytes are primarily phagocytes and express high levels of the ACE-2 receptor . Therefore, they could either phagocyte viral particles and apoptotic virally infected cells or be potential targets for SARS-CoV-2 infection. Considering their short circulating lifespan, viral protein-containing classic monocytes turn into intermediate and nonclassical monocytes.
According to the study results, this process happens faster in the severe group than in the PASC group. Indeed, at early stages of the disease the severe group show increased nonclassical monocytes whereas in PASC both the intermediate monocytes and non-classical monocytes are elevated.
Additionally, CD14+CD16+ monocytes express intermediate levels of ACE-2 receptors and could as well serve as an infectious target of SARS-CoV-2 as it has been proved to be an infectious target of HIV-1 and HCV.
Nonclassical monocytes have been proposed to act as custodians of vasculature by patrolling endothelial cell integrity, thus pre-existing CD14+ and CD16+ cells could ingest virally infected apoptotic endothelial cells augmenting the proportion of nonclassical monocytes containing S1 protein. This mechanism is more likely to take place in the PASC group where the S1 protein was detected 12-15 months post infection than in the severe group.
Furthermore, nonclassical monocytes are associated with FcR-mediated phagocytosis, which might be related with the ingestion of opsonized viral particles after antibody production at later stages of the disease in PASC.
Previous reports indicate that the numbers of classical monocytes decrease, but the numbers of intermediate and non-classical monocytes increase in COVID-19 patients.
Hence, the presence of S1 protein in nonclassical monocytes in both severe and PASC, might be associated with clinical characteristics and outcome of these groups.
Previously, the team found that individuals with severe COVID-19 have high systemic levels of IL-6, IL-10, VEGF and sCD40L5. Consistent with the study data, other studies showed association of increased production of IL-6, VEGF and IL-10 by nonclassical monocytes with disease severity. In the case of PASC, the persistence of circulating S1-containing nonclassical monocytes up to 16 months post infection, independently of the different possible mechanisms of viral proteins internalization discussed above, indicates that certain conditions are required to maintain this cell population.
It has been shown in both humans and mice that nonclassical monocytes require fractalkine (CX3CL1) and TNF to inhibit apoptosis and promote cell survival.
Previous data show high IFN-γ levels in PASC individuals, which can induce TNF-α production.
Further, TNF-α and IFN-γ induce CX3CL1/Fractalkine production by vascular endothelial cells creating the conditions to promote survival of nonclassical monocytes. Another important aspect is the permanency of S1-containing cells in the circulation, intermediate monocytes express high levels of CCR5 and extravasation of these cells can occur in response to CCL4 gradients.
The study team showed that PASC individuals have low levels of CCL45 maintaining these cells in circulation until they turn into nonclassical monocytes. Moreover, IFN-γ induced CX3CL1/Fractalkine production by endothelial cells creates a gradient within the vascular compartment preserving nonclassical monocytes expressing CX3CR1 in the circulation.
Nonclassical monocytes are usually referred as anti-inflammatory cells, nevertheless it was recently shown that this subset can acquire a proinflammatory phenotype .
Nonclassical monocytes acquire hallmarks of cellular senescence, which promote long term survival of these cells in circulation as explained above. Additionally, this induces an inflammatory state of the non-classical monocytes that could be a manifestation of the senescence-associated secretory phenotype (SASP), characterized by a high basal NF-κB activity and production of proinflammatory cytokines such as IL-1α, TNF-α and IL-8.
The hallmark of PASC is the heterogeneity of symptoms arising in a variety of tissues and organs. These symptoms are likely associated with the inflammatory phenotype of these senescent nonclassical monocytes. The CD14lo, CD16+, S1 protein+ monocytes could be preferentially recruited into anatomic sites expressing fractalkine and contribute to vascular and tissue injury during pathological conditions in which this monocyte subset is expanded as previously demonstrated in non-classical monocytes without S1 protein. Previously, CD16+ monocytes were demonstrated to migrate into the brain of AIDS patients expressing high levels of CX3CL1 (fractalkine) and SDF-1 , and mediate blood-brain barrier damage and neuronal injury in HIV-associated dementia via their release of proinflammatory cytokines and neurotoxic factors.
These sequelae are very common in PASC and these data could represent the underlying mechanism for the symptoms. Interestingly, a number of papers have been written discussing the increased mobilization of CD14lo, CD16+ monocytes with exercise. These data support the reports of worsening PASC symptoms in individuals resuming pre-COVID exercise regimens.
In summary, the mechanism of PASC discussed in this report suggests that intermediate monocytes remain in circulation due to low CCL4 levels extending their time to differentiate leading to an accumulation of non-classical monocytes. The utility of using CCR5 antagonists in preventing migration of intermediate and non-classical monocytes due to the elevated levels of CCL5/RANTES in PASC.
Further, the study findings suggests that interruption of the CX3CR1/fractalkine pathway would be a potential therapeutic target to reduce the survival of S1-containing non-classical monocytes and the associated vascular inflammation previously discussed and presented here.
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