Urgent And Detailed Research Warranted On Enigmatic Role Of Depleting Levels Of The Macrophage-Derived Chemokine MDC/CCL22 In COVID-19

COVID-19 News: In the sprawling realm of immunology, the Macrophage-Derived Chemokine, known as MDC or CCL22, is a significant player. Belonging to the CC subfamily, this chemokine is produced by dendritic cells and macrophages, with or without external stimulation. The Saint Petersburg Pasteur Institute and Pavlov First State Medical University in Russia have spearheaded groundbreaking studies on the puzzling dynamics of MDC/CCL22 in the course of COVID-19 but still further detailed studies are warranted of the role of depleting levels of this macrophage-derived chemokine in COVID-19 and the effects it has on the human host in the long term health especially in terms of cancer and whether the  decreased levels of this chemokine seen even in Post COVID individuals would help the progression of cancers and also other health issues.


 Possible mechanisms for lower MDC/CCL22 concentrations in COVID-19 patient plasma. I
- decrease in MDC/CCL22 concentration associated with selective binding to SARS-CoV-2 viral
peptides. II - restriction of MDC/CCL22 secretion by producer cells due to their functional failure

Amid the global turmoil of the COVID-19 pandemic, these research findings by the Russian study team underscore an enigmatic anomaly: a profound depletion of MDC/CCL22 concentrations. Intriguingly, these shifts in concentrations demonstrate remarkable stability, regardless of the SARS-CoV-2 variant in question, and persist even in convalescent patients. The cause and significance of this mysterious phenomenon are yet to be fully understood, sparking a flurry of speculation and hypothesis.
 
At the heart of the COVID-19 disease is the SARS-CoV-2 virus. This cunning invader breaches the cell's defenses through membrane fusion or viral particle uptake, kickstarting a cascade of immune responses. Crucial to this process are the ACE2, TMPRSS2, and NRP1 cellular receptors, which facilitate membrane fusion and enable the virus to infiltrate the host cell's cytoplasm. Once inside, the virus triggers inflammation by interacting with the ACE2 receptor, potentially setting off a ‘cytokine storm’ - a hyperinflammatory reaction often linked with severe COVID-19 that has been covred in may past peer reviewed published studies and COVID-19 News reports.
 
Amidst this maelstrom of immune reactions, MDC/CCL22 has a pivotal role to play. This chemokine acts as a potent chemoattractant for immune cells and is key to chronic inflammation. It is primarily produced by maturing dendritic cells and activated monocytes/macrophages, playing a crucial role in cellular migration and Th1/Th2 polarization. Yet, in a curious departure from the norm, COVID-19 patients consistently exhibit significantly lower MDC/CCL22 concentrations.
 
Investigations reveal that these reduced concentrations persist even in convalescent patients, with levels remaining notably lower than those in healthy individuals. This persistent deficiency suggests that SARS-CoV-2 leaves a lasting imprint on the immune system, potentially contributing to immune dysregulation and severe pulmonary pathology.
 
Beyond the scope of COVID-19, MDC/CCL22 has been the subject of extensive research in oncology. Its critical role in recruiting immune cells to tumor sites has prompted exploration of its potential as a target for monoclonal antibody therapy. Additionally, in autoimmune and atopic diseases, MDC/CCL22 is typically overexpressed, leading to the recruitment of immune cells to target tissues and intense expression of pro-inflammatory markers.
 
MDC/CCL22 also plays a significant role in respiratory diseases, such as tuberculosis, where it shows lower concentrations in vitro in cells from infected patients. In patients with lung cancer, high levels of MDC/CCL22 are associated with positive post-surgical outcomes.
 
However, in the case of COVID-19, MDC/CCL22 levels decrease, underscoring the unique nature of this disease.
 
The research teams postulate two plausible mechanisms for this puzzling reduction in MDC/CCL22 concentrations in COVID-19 patients. The first hypothesis revolves around the potential binding of SARS-CoV-2 viral proteins with MDC/CCL22 due to potential affinity with, or mimicry of, MDC/CCL22's main ligands. In such cases, the chemokine's production remains unaffected, but its functional activity may be reduced due to changes in its antigenic structure. This could effectively render it invisible to commercial detection kits. This theory gains credence as other cytokines and chemokines, produced by dendritic cells and macrophages, show enhanced expression compared to healthy donors.
 
Interestingly, the virus needs mechanisms to evade immune responses, and one potential strategy could be to block chemoattraction by inactivating chemokines.

Alternatively, the mysterious drop in MDC/CCL22 could be explained by the second hypothesis: the virus could directly impact the functional activity of macrophage-derived chemokine producer cells. Research shows a significant deficiency of dendritic cells in COVID-19 patients during both the acute and post-recovery phases. This shortage is not just numerical but also qualitative, as in vitro studies reveal a reduction in dendritic cell functionality.
 
The complex dynamics of COVID-19 and MDC/CCL22 interaction opens a Pandora's box of questions. The SARS-CoV-2 virus is known to suppress dendritic cell function and MDC/CCL22 production, but the precise mechanisms remain shrouded in mystery.
 
The persistent deficiency of MDC/CCL22 in the blood plasma of COVID-19 patients when compared to healthy donors suggests this chemokine may play a critical role in the pathogenesis of the disease. A detailed understanding of this intriguing interplay could potentially pave the way for developing new therapeutic strategies to combat COVID-19 and other infectious diseases.
 
MDC/CCL22 serves as a mediator for both Th2 immune responses and regulatory T cells. A deficit of this chemokine could potentially tilt the balance of the inflammatory response towards hyperactivation. The noticeable depletion of MDC/CCL22 concentrations in the blood plasma of acute COVID-19 patients might explain the relatively greater severity of COVID-19 compared to other respiratory viral infections.
 
The unique role of MDC/CCL22 in COVID-19, especially its intriguing reduction in concentration, presents a compelling case for further investigation. This chemokine could potentially be the missing link in our understanding of COVID-19's complex immunological processes. Its role in the formation of vaccine-associated immunity, particularly in individuals who have survived severe COVID-19, cannot be overstated. As MDC/CCL22 concentrations tend to decrease in association with COVID-19, a hyperinflammatory profile and an inadequate reaction to external stimuli may present potential challenges in immunity formation.
 
In the labyrinth of COVID-19 research, the role of MDC/CCL22 stands as a riddle wrapped in an enigma. While we are on the precipice of new discoveries, further research is needed to fully comprehend the role and dynamics of MDC/CCL22 in COVID-19. The journey towards unearthing these answers will undoubtedly pave the way for more effective treatment strategies, ultimately bringing us one step closer to winning the war against COVID-19.
 
The Russian study findings were published on a preprint server and definitely warrants further investigations and research.
https://www.preprints.org/manuscript/202305.0420/v1
 
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