# Immunomodulatory Effects of Pentoxifylline: Profiling Data Based on RAW 264.7 Cellular Signaling
## 4 Discussion
PTX activates the adenosine A2A receptor, which is expressed by many types of immune cells, endothelial cells, and platelets, thereby up-regulating anti-inflammatory and anti-thrombotic molecules, and finally inhibiting the cytokine storm syndrome, which is believed to be the main pathogenic mechanism of COVID-19's lethal complications [26]. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an RNA virus genetically located within the genus Betacoronavirus that uses a glycoprotein (spike protein) to bind to the angiotensin-converting enzyme 2 (ACE2) receptor. After binding, the serine protease TGRBBS2 facilitates virus entry into the cell [37]. Currently, no therapeutic agent is effective in treating the SARS-CoV-2 infection, but the classes of drugs that are used include antiviral agents, neuraminidase inhibitors, and anti-inflammatory drugs [38]. As an antiviral agent, Lopinavir/ritonavir is an antiretroviral of the protease inhibitor class and is mainly used in COVID-19 patients with less severe symptoms and also in the early stage of the disease. Remdesivir, which belongs to the class of nucleotide analogs, was previously used in the Ebola virus epidemic in Africa and is currently used in moderate and severe COVID-19 [39]. As immunomodulatory drugs, an abnormal release of pro-inflammatory cytokines such as interleukin-6 (IL-6), interferon-gamma, and tumor necrosis factor-alpha was observed in moderate to severe stage COVID-19 patients. Anti-inflammatory drugs (particularly monoclonal antibodies) are used in COVID-19 patients. In this category, anti-IL6 (Tocilizumab), anti-IL-1 (Anakira), JAK inhibitors (Baricitinib), corticosteroids, antimalarialials (Chloroquine/Hydroxychloroquine), heparins, and immunoglobulins. Antiviral agents are useful to inhibit the clinical progression and complications of COVID-19. Clinical and survival improvements were found in patients treated with plasma and hyperimmune immunoglobulins. Inflammation inhibitors are candidates for the treatment of advanced-stage COVID-19 [39]. Most patients with severe COVID-19 show elevated serum levels of pro-inflammatory cytokines including IL-6, IL-18, IL-2, IL-8, IL-17, G-CSF, GM-CSF, MCP1, and TNF, characterized as cytokine storm [40]. A number of studies have trialed plans to reduce inflammatory responses. As already mentioned, PTX is derived from a methylxanthine derivative that inhibits phosphodiesterase-4 (PDE-4). PTX functions as a hemorrhage agent and affects immunomodulation, inflammation, and oxidative stress [41]. In this study, the expression levels of IL-1, IL-6, M-CSF, MCP-1, MMP-10, and COX-2 were significantly down-regulated by PTX treatment in RAW 264 cells. Inhibition of proinflammatory cytokines by PTX treatment shares a context to other immunomodulatory agents used in COVID-19. The levels of CD4 and IL-10 were increased and PTX was found to increase immune function. In addition, the proliferation of macrophages is inhibited by PTX treatment, the macrophage-related acute immune response can be suppressed (Figure S2). The expressions of IGF1, HER1, and HER2 in growth factor-related protein expressions were slightly up-regulated. The expression levels of FGF-1 and FGF-2 were significantly reduced after PTX treatment. When PTX was applied to a renal fibroblast cell line, it inhibited fibroblast proliferation and suppressed FGF-2 synthesis [42]. Clinical studies on radiation-induced fibrosis have also shown that circulating the FGF-2 level was reduced after eight weeks of PTX treatment [43]. Tissue hypoxia can induce macrophage infiltration,which is a source of pro-fibrotic mediators, including TGF-\(\beta\)1 [44]. In this study, TGF-\(\beta\)1 expression was not significantly affected by PTX treatment. The expression of CRP-1, CD4, IL-10, MMP-1, MMP-2, MMP-3, and MMP-9 was upregulated in inflammation-related protein profiles. The expression levels of IL-1, IL-6, CD3, CD28, M-CSF, MCP-1, MMP-10, hepcidin, cathepsin K, LTA4H, CXCR4, and COX-2 were all down-regulated by PTX treatment.