SARS-CoV-2 and Covid-19 Immunopathogenesis

19 The coronavirus disease 2019 (COVID-19) is now a global pandemic caused by the new severe acute 20 respiratory syndrome coronavirus 2 (SARS-CoV-2). Unlike other known coronaviruses, such as the 21 Middle East respiratory syndrome coronavirus (MERS-CoV), SARS-CoV-2 reveals new clinical, 22 immunological, and pathologic features. The lymphocyte depletion, macrophage and neutrophil 23 hyperactivation, cytokine dysregulation, thrombophilia, delayed antiviral response, and immune 24 exhaustion are key immunological findings linked to the clinical progression of this disease. 25 Understanding and identifying the underlying immunological basis of COVID-19 is crucial to 26 designing effective therapies. Here, we provide an overview of immunopathogenesis driven by SARS27 CoV-2 after its interactions with the immune system. 28

tropism beyond the respiratory tract, including the kidneys, liver, heart, and brain (25). The initial 76 examination of lung specimens from the early phases of COVID-19 reveals some important 77 histological changes: (1) interstitial edema and proteinaceous and fibrin exudate; (2) 78 reactive pneumocyte hyperplasia with patchy inflammatory cellular infiltration, corresponding to the 79 ground-glass radiology findings; (3) thickening of alveolar walls and septa due to fibroblastic 80 proliferation and type II pneumocyte hyperplasia, consistent with early diffuse alveolar damage 81 patterns; and (4) abundant macrophage infiltration (26). Later stages have shown bilateral diffuse 82 The ACE2 was discovered in 2000 by two different groups of scientists (49). This enzyme is a zinc 137 metalloproteinase and key regulator of the renin-angiotensin system (RAS). It has, in its catalytic 138 domain, 42% identical residues compared to endothelial ACE (50; 51). ACE2 cleaves only one amino 139 acid from angiotensin I (ANG) to form angiotensin (1-9), which is then converted to Angiotensin II by 140 ACE (52). There is another important action of ACE2, which is metabolized ANG II to form peptide 141 ANG (1-7), a vasodepressor responsible for decreasing the vasopressor peptide ANG II levels in the 142 circulatory system and tissues. Additionally, the activity and action of ACE2 are not affected by ACE 143 inhibitors, further distinguishing ACE2 from the classic ACE (53). Therefore, the pathophysiology of 144 ACE2 needs to be explored when it comes to understanding cell infection and the influence of COVID-145 19 on the body. 146 The immunopathogenesis of COVID-19 is related to the ACE2 receptor in the following ways: (1) it 147 affects many tissues as it is widely distributed and expressed at higher levels in at-risk groups with 148 comorbidities, (2) the use of the receptor can cause downregulation that influences RAS homeostasis, 149 (3) the binding between the virus and ACE2 modulates tumor necrosis factor (TNF)-α-converting 150 enzyme (TACE) activity and (4) ACE2 tissue distribution (54; 55; 56; 57; 49). 151

Tissue distribution and expression according to comorbidities 152
ACE2 is expressed on the apical surface of type II alveolar cells of the lung, esophagus epithelial cells, 153 enterocytes from the ileum and colon, cholangiocytes, myocardial cells, endothelium of the coronary 154 and intrarenal vessels, kidney proximal tubule cells, bladder urothelial cells, and tongue 155 epithelium (55). ACE2 is also found in central nervous system cells, indicating that SARS-CoV-2 156 affects neuronal cells after brain invasion via the olfactory epithelium (58). This tissue distribution 157 explains the wide multiorgan virus tropism of SARS-CoV-2 (59). 158 Older patients with comorbidities, such as systemic hypertension, diabetes mellitus (DM), obesity, and 159 respiratory diseases, as well as smokers and those with chronic obstructive pulmonary disease 160 (COPD) (56; 57; 49), have a greater risk of developing the severe form of the disease. There is also a 161 correlation between ACE-2 and a poor prognosis in pregnant women. 162 The expression of ACE2 is substantially increased in patients with type 1 or type 2 diabetes who are 163 treated with ACE inhibitors and angiotensin II type I receptor blockers (56). Most studies have shown 164 that DM is associated with more severe cases of COVID-19 and other viral infections, acute respiratory 165 distress syndrome (ARDS), and increased mortality. These patients are more likely to be older than 166 those without type II DM. Diabetes has a notable immune effect on the body, especially on the innate 167 immune response, the first line of defense against viruses, and it has been associated with exaggerated 168 pro-inflammatory cytokine responses (notably interleukin (IL)-1, IL-6, and TNF-α)(60). 169 Systemic hypertension is associated with a severe form of COVID-19. A study enrolled 1,099 patients,  170 of whom 173 had a severe disease with comorbidities, such as hypertension (23.7%) and coronary heart 171 disease (5.8%) (9). Another study showed that among 140 patients who were COVID-19-positive, 30% 172 had hypertension (61). Another study enrolled 78 patients with mild to moderate heart failure and found 173 that the myocardium of these patients that had dilated or those who had ischemic cardiomyopathy had 174 significantly increased expression, at mRNA and protein levels, of ACE and ACE2 compared to the 175 control group (62). 176 Obesity is another risk factor that can lead to severe complications in SARS-CoV-2 infections (57). 177 The ACE2 expression is higher in adipose tissue than in lung tissue (63). Individuals with obesity have 178 more adipose tissue, so have an increased number of ACE2-expressing cells and, consequently, a 179 higher predisposition to more severe infections by SARS-CoV-2 (64). 180 Most of the severe cases of COVID-19 have been described in those over the age of 55 years with 181 significant comorbidities, such as COPD. ACE-2 expression in the human small airway epithelium was 182 significantly increased in those with COPD compared to non-smokers, but not in healthy smokers (49 Within the endosome, the S1 and S2 subunits carry out processes that culminate in the fusion of the 228 viral membrane and the release of its content into the host cytoplasm. The S1 subunit is cleaved, 229 exposing the fusion peptide, which inserts itself into the host membrane. The S2 region folds over itself 230 to bring together the HR1 and HR2 regions, which merge to participate in the viral fusion process (82; 231 83; 84; 85). The viral entry is coupled with TNF-α production (86). In contrast, using a variety of 232 pattern recognition receptors (PRRs), alveolar epithelial cells and alveolar macrophages detect the 233 pathogen-associated molecular patterns (PAMPs), such as viral RNA, and damage-associated 234 molecular patterns (DAMPs), including ATP, DNA, and ASC oligomers, initiating the innate immune 235 response (Figure 1). 236 The PRRs that integrate the recognition systems of PAMPs and DAMPs across the cell surface are toll-237 like receptors (TLR) 1, 4, and 6, which activate the signaling pathway, leading to the activation of NF-238 kB and IRF3/IRF7, and the subsequent expression of pro-inflammatory cytokines and type I   has a role in autoimmune diseases, such myocardial infarction and metabolic syndromes (101). 287 TNF is produced by T cells, NK cells, macrophages, and monocytes. The principal receptor is TNFR1 288 (55 kD) and TNFR2 (75 kD) and the binding of TNF-α and TNF-β with it triggers inflammatory 289 reactions (101). TNF-α can provoke blood clotting, leading to disseminated intravascular coagulation 290 (102). 291 IL-6 can promote the differentiation of CD4+ T cells via IL-21 production into Th17 effector cells. 292 The increase of Il-6 levels in septic patients is correlated with gravity and organ failure (102). 293 Additionally, IL-6 also suppresses Major Histocompatibility Complex (MHC) class II expression in 294 dendritic cells via STAT3 activation (104). 295 According to previous studies, SARS-CoV-2 has a high inflammatory characteristic associated with 296 macrophages and neutrophils, mainly due to the release of pro-inflammatory cytokines (105). The 297 maintenance of this inflammatory state, especially in the presence of pro-inflammatory cytokines, is 298 related to tissue damage in multi-organs, septic shock, and circulatory failure (106; 44). 299  pathways, such as IL23A and CD74, were reduced in terms of abundance in the patient with altered 327 chest radiographs (111). 328

Antigen-presenting cells (APCs) and the virus
High levels of IL-6 were identified in patients with more severe COVID-19 (112). IL-6 inhibited HLA 329 D-related (HLA-DR) expression (104) and the low expression of HLA-DR on CD14 monocytes is 330 characteristic of sepsis-induced immunoparalysis (113). In patients with pneumonia caused by SARS-331 CoV-2 when the number of molecules of HLA-DR on CD14 monocytes decrease, severe respiratory 332 failure proceeds, which leads to the idea that high levels of IL-6 mediate the low expression of HLA-333 DR on CD14 monocytes of patients with severe COVID-19, affecting the antigen presentation to T 334 CD4+ naive cells (114). Interestingly, the IL-6 inhibition with tocilizumab restores the expression of 335 HLA-DR expression and antigen presentation, partially rescuing SARS-CoV-2-associated immune 336 dysregulation (115). 337 but recognized as possible inhibitors. ORF 3b inhibits IFN-β production mediated by RIG-I and 353

Viral escape mechanisms
MAVS, but not that which is mediated by TNF-α, and ORF 6 blocks nuclear translocation of the 354 transcription factor STAT1 that interrupts the IFN pathway (120; 121). SARS-CoV-2 presents the 355 capacity to produce nps 1-16 and the same ORF 6, but not ORF 3b (122), thus, this mechanism of 356 exhaustion and the similarity of SARS-CoV-2, SARS-CoV, and MERS can assist in the development 357 of treatment against SARS-CoV-2. Collectively, SARS-CoV-2 induces delayed INF and Th1 358 responses. The delayed IFN response may also account for the shift of Th1 to Th17 lymphocytes, 359 leading to tissue accumulation of neutrophils and an increase in the neutrophil:lymphocyte ratio in 360 blood (123). 361

Lymphocyte and cell depletion during COVID-19 362
Lymphocytes constitute protection for an organism by being part of the adaptive immunity and forming 363 a humoral immune response by B lymphocytes or cell mediation by T lymphocytes. Normally, from 364 the identification of the viral epitope by the APC, the T lymphocytes are activated via the TCR, and 365 proliferates and differentiates into Th1 cells, becoming effector T cells acting on cell-mediated 366 immunity for intracellular pathogens. B lymphocytes, on the other hand, will activate through the APC 367 and become Ab-producing cells, resulting in humoral immunity. Both immunities appear around the 368 third day of infection and act to eliminate the antigen. SARS-CoV-2 appears to dump cellular and 369 humoral responses depleting lymphocytes. 370 The new infection caused by SARS-CoV-2 reaches this lymphocyte barrier, generating 371 lymphocytopenia through several defense mechanisms. Lymphocytopenia is a common marker 372 presented by patients with COVID-19. A previous study indicated the presence of positive regulation 373 in the mechanisms of autophagy, apoptosis, and p53 in peripheral blood mononuclear cells (PBMCs), 374 mostly lymphocytes and a smaller number of monocytes, resulting in lymphocyte depletion (124). In 375 terms of comparison, the MERS produced by MERS-CoV is capable of generating apoptosis of 376 primary T lymphocytes through the extrinsic and intrinsic pathways, but it cannot replicate within the 377 lymphocytes. SARS-CoV-2 is believed to have a similar mechanism that results in lymphocytopenia. 378 SARS-CoV-2 infection of lymphocytes is more competent compared to SARS-CoV. Protein S can 379 considerably increase infection even in cells with low expression of hACE2 (125). However, 380 lymphocytic infection is not limited to a single mechanism, as it was discovered that the new virus can 381 infect T cells through the endocytosis pathway mediated by receptors, such as HR1, or through the 382 fusion of membranes through the spike protein and its subunits. The S1 subunit assists in binding to 383 the receptor and the S2 subunit facilitates membrane fusion. 384 Studies involving flow cytometry to evaluate cell phenotypes in patients with COVID-19 have resulted 385 in markedly reduced total T cell number, B cell, and NK cell cellularity, more intensely in severe cases. overproduction is linked to disease severity and fatal outcomes (138). IL-6 is significantly increased in 434 these patients and continues to increase over time, mostly derived from lung-accumulated macrophages 435 and neutrophils, being relatively more elevated in non-survivors than survivors (71; 139; 140). This 436 abnormal cytokine and chemokine production leads to a cytokine storm profile with uncontrolled 437 inflammation ( Figure 3 and Figure 4)  respectively. In the course of the first two weeks, Ab levels and seroconversion rates increased fast, as 535 the cumulative seropositive rate hit 50% on day 11 and 100% by the day 39 of disease onset (159). 536 However, another study found that 100% of patients were positive to virus-specific IgG around 17-19 537 days after symptom onset. Interestingly, for IgM, the peak took more days to occur and was a little 538 lower, reaching 94.1% by days 20-22. No association between plateau IgG levels and the clinical 539 characteristics of the patients was found. A small number of patients initially presented as seronegative; 540 however, by the end of the third week all patients achieved seroconversion of IgG or IgM (160). 541 Regarding Ab levels at the late stage of the infection and their association with virus clearance, it was 542 shown, in agreement with data presented previously, that IgG was first detected within an average of 543 15 days. The IgM begins to decline and reaches lower levels by week five, and almost disappears by 544 week seven, whereas IgG persists beyond seven weeks (161). Most importantly, it has also been found 545 that SARS-CoV-2 can coexist with specific Abs for 36-50 days, which leads to a new question: how 546 can the virus circulate in the presence of these for such a long time? Additionally, it enhances the 547 importance of innate and adaptative immunity in the resolution of COVID-19 (162). 548 Severe cases of COVID-19 are more frequently found in patients with high levels of IgG (51.8%) 549 compared to those with lower levels (32.3%). With these findings, it is proposed that the Ab response 550 might be linked to secondary organ damage, other than the antiviral activity (163). Additionally, the 551 association between IgG levels and the severity of symptoms, a positive correlation with Ab titers for 552 two weeks after onset, was found. It is suggested that high Ab levels alone might be a risk factor, 553 separate to other known risk factors, such as the presence of comorbidities, being elderly, and being 554 male (159). The combined detection of specific IgM and IgG against viral nucleotides (N-IgM, N-IgG) 555 and spike proteins (S-IgM, S-IgG) can be used as an efficient method of early detection of SARS-CoV-556 2 infection since the seropositive rate of these four Abs combined reaches 75% after the first week. By 557 the third week, the seropositive rates of N-IgG and S-IgG hits 100% (164). Thereafter, the most 558 sensitive and earliest serological marker is total Abs, levels of which begin to increase from the second 559 week of symptom onset (165). 560 The impact of these specific Abs in predicting a patient´s prognosis is another point debated in the 561 same study. After analyzing blood samples from 38 patients (both ICU and non-ICU patients), 562 differences were observed in the IgM to IgG class-switch between these two groups that might reflect 563 distinct clinical outcomes. The ICU group presented an elevated production of N-IgM and N-IgG, but 564 lower levels of S-IgG compared to non-ICU patients. High N-IgG levels are believed to indicate more 565 severe illness than S-IgG levels, and, thus, a worse prognosis. On the other hand, non-ICU patients 566 switched from IgM to IgG more quickly and showed a positive correlation between the increase of S-567 IgG and decrease of C-Reactive Protein (CRP) (a protein that marks systemic inflammation) (164). 568 The neutralizing Ab (NAb) response, especially spike binding Ab levels (targeting RBD, and subunits 569 S1 and S2) has been evaluated through the plasma analysis of 175 recovered patients of SARS-CoV-570 2. Interestingly, around 30% of these patients generated a very low level of NAb titles, with one third 571 of them being below the limit of detection and not developing NAbs afterward. Elderly patients, on the 572 other hand, had higher levels of NAbs and these were negatively correlated with lymphocyte counts 573 and positively correlated with blood CRP levels (166). 574 Although the RT-PCR test has been used as a standard method to diagnose SARS-CoV-2 infection 575 globally, the reports of false-negative cases are afflicting and epidemiologically threatening. A Chinese 576 study analyzed 610 patients diagnosed with COVID-19 by the recommended protocol. In the first test, 577 at least 63.0% (384) of the patients returned negative PCR results and 57 were dubiously positive 578 (9.3%). In addition, 18 patients had a positive result after two consecutive negative results, showing an 579 oscillating pattern (167). Therefore, the search for a better understanding of more specific methods of 580 diagnosis has grown. Therefore, the measurement of virus-specific total Abs, as well as IgG and IgM, 581 represents the false-positive that labels persons erroneously as having COVID-19 with unnecessary quarantine 594 and (2) the false-negative that is especially harmful due to misidentification of infected persons. 595 Therefore, validation should be addressed for the available and developing tests as a way to improve 596 public health measures of epidemic control. 597

Does SARS-CoV-2 induce immunity? 598
One of the biggest questions surrounding SARS-CoV-2 is whether the immune system develops long-599 lasting immune responses after infection. As it has only been a few months since the spread of the 600 virus, there is not currently sufficient evidence to answer this question, and further studies are needed. 601 One of the main concerns is that other CoVs, such as SARS-CoV, showed a relatively low extent of 602 immune response after infection (170 CoV-2 through a post-pandemic period predicted a short duration of immunity (172). Therefore, the 607 immune protection against these viruses may wane over time and immune protection after re-exposure 608 is uncertain. 609 Remarkably, patients who recently recovered from the infection displayed serum neutralizing activities 610 in a pseudotype entry assay, indicating mounted IgG and IgM responses to SARS-CoV-2 proteins, 611 especially nucleocapsid protein and RBD of S protein, suggesting that the IgG amounts could be 612 sustained for at least two weeks after discharge. Additionally, this suggests that most patients post-613 discharge have serum-neutralizing SARS-CoV-2 infections (173). It has also been shown that IgG 614 specific to SARS-CoV-2 trimeric spike protein titers raised over the first three weeks from symptom 615 onset, and fell during the second month after symptom onset but remained detectable (174). 616

RBD-specific monoclonal Abs (mAbs) derived from single B cells of eight SARS-CoV-2-infected 617
patients showed potent neutralizing activity against pseudoviruses and lived SARS-CoV-2. It has also 618 been demonstrated that none of the SARS-CoV-2 Abs nor the infected plasma cross-reacted with RBDs 619 from either SARS-CoV or MERS-CoV, suggesting that the Ab response to RBDs is viral and species-620 specific (175). Over 1,100 isolated S-protein specific-memory B cells derived from seven COVID-19 621 convalescent donors showed that even though the frequency of S-protein specific-memory B cells is 622 This is a provisional file, not the final typeset article highly variable among donors, SARS-CoV-2-specific mAbs can be successfully isolated from most of 623 them. Additionally, 17 of the mAbs were able to effectively neutralize SARS-CoV-2 with high potency 624 when tested in vitro (176). 625 A recent study from China has demonstrated the lack of reinfection in rhesus monkeys after being 626 submitted to a rechallenge infection of SARS-CoV-2 28 days post-initial challenge. The levels of Abs 627 against SARS-CoV-2 were significantly higher 14 days post-rechallenge compared to 28 days after the 628 initial infection. Additionally, there were no significant pathological findings that could be attached to 629 possible reinfection. Although the results of this study were promising, there is a lack of evidence that 630 the effects of a rechallenge would remain the same after an interval longer than six months (177). 631 Moreover, emerging data comparing asymptomatic and symptomatic patients adjusting for individual 632 characteristics are showing that IgG levels and neutralizing Abs start to decrease 2-3 months after the 633 infection begins. These data indicate the risks of an "immune passport", relaxing public health 634 measures, such as social distancing and widespread immune tests, and high-risk groups' isolation (18). inflammation that activates more macrophages, causing hemophagocytosis, leading to multi-organ 660 dysfunction and poor outcomes. Other features of MAS are not usually present in patients with 661 COVID-19, such as hepatomegaly and splenomegaly, which may indicate a higher state of 662 inflammation in the lungs. 663 An autopsy series correlating clinical and laboratory findings studied the reticuloendothelial organs 664 (spleen, liver, and multiple pulmonary hilar/mediastinal lymph nodes) of four patients who died of 665 COVID-19. Three cases had histological evidence of hemophagocytosis within pulmonary 666 hilar/mediastinal lymph nodes, and one case showed hemophagocytosis in the spleen, but none showed 667 hemophagocytosis in the liver or bone marrow. It was also found that lymphophagocytosis was the 668 predominant form of hemophagocytosis. The clinical and laboratory data of one patient showed 669 diagnostic features of hemophagocytic lymphohistiocytosis (HLH) with an H-score of 217, while a 670 second patient was likely HLH with a partial H-score of 145 due to missing triglyceride levels (183). 671

Neutrophils and SARS-CoV-2-induced neutrophil-derived extracellular trap (NET) 672
formation 673 The increased number of neutrophils is related to the severity of the respiratory syndrome and adverse 674 outcomes in COVID-19 (9). NET formation is a key factor in tissue damage and organ failure during 675 sepsis (184). NETs are networks of fibers composed of nuclear chromatin, nuclear histones, and 676 granular anti-antimicrobial proteins. The NETs are triggered by activated PRR or chemokines, 677 followed by ROS production and calcium mobilization (185). During NET formation, large amounts 678 of ROS, myeloperoxidase, and elastase were released, with the aim to trap and kill pathogens (186). should be explored as a therapeutic target (192; 186). 693

COVID-19 and hyperferritinemia 694
The severe form of COVID-19 is believed to be a part of the "hyperferritinemia syndrome" group 695 since it presents features of high serum ferritin and systemic hyper-inflammation. The other four 696 entities comprehended under this term include MAS, adult-onset Still's disease (AOSD), catastrophic 697 anti-phospholipid syndrome (CAPS), and septic shock. Since these conditions share a common 698 pathogenic background, COVID-19 patients could benefit from a similar therapeutic approach, 699 including anti-inflammatory and immunomodulatory agents (193). In a study from China conducted 700 with 21 severe COVID-19 patients, tocilizumab presented itself as an effective treatment, improving 701 symptoms, and repressing clinical deterioration (194). 702 In order to understand the mechanisms of serum ferritin secretion and its relationship with 703 inflammation, an experiment analyzing mouse serum ferritin secretion concluded that serum ferritin is 704 not only a result of a cellular leak, but also actively secreted by macrophages through a nonclassical 705 secretion process involving secretory lysosomes. After lysosomal processing, ferritin can be further 706 degraded or secreted by cells that have a lysosomal secretory pathway, such as cells from the 707 hematopoietic lineage (including macrophages) or renal tubular cells. Genetic findings with 708 macrophages and the iron regulatory protein 2 (IRP2), and the fact that splenectomy caused decreased 709 serum ferritin concentrations in mice, supported that macrophages contribute significantly to serum 710 ferritin. Further evidence includes demonstrations that primary cultures of bone marrow-derived 711 macrophages secrete ferritin into their culture medium. The results obtained seem to explain that serum 712 ferritin is elevated in inflammation when increased hepcidin levels inhibit iron recycling from 713 macrophages (195). In AOSD, high ferritin serum levels and findings of ferritin expression in the 714 lymph node B area have been described, suggesting that macrophage activation might be related to 715 hyperferritinemia (196). 716 A study aiming to evaluate clinical characteristics of infection markers in severe and very severe 717 patients with COVID-19 showed that both groups exhibited increased serum ferritin levels, but the 718 serum ferritin in the very severe COVID-19 group was significantly higher (1006.16 ng/ml) than that 719 of the severe COVID-19 group (291.13 ng/ml). This increase in ferritin levels might be related to severe 720 secondary bacterial infection in COVID-19 and a poor prognosis (197). 721

Role of HGMB-1 and TF in thrombotic events 722
High mobility group box 1 protein (HMGB-1) is an endogenous DAMP protein that can induce 723 inflammation. HMGB-1 can be produced and released by damaged or dying cells and is involved in 724 the innate immunity system. A study from 2015 sought to investigate platelet-derived HMGB1 with 725 transgenic mice with platelet specific HMBG-1 ablation. It was reinforced that platelets store and 726 express HMGB1 on their surfaces after activation and mediate platelet aggregation and thrombosis. It 727 was also shown that the prothrombotic effect was mediated via platelet . described (201). 736 Considering the high number of reported cases on thrombosis related to COVID-19, a possible 737 pathological mechanism is an association with HMGB1. A similar hypothesis was proposed for SARS-738 CoV in 2004. In this case, HMGB1 was related to lung injury and its release from endothelial alveolar 739 damaged cells and innate immunity cells (such as macrophages and monocytes) (202). Due to its 740 relationship to various SARS-CoV-2 symptoms and mortality, scientists point to HMGB1 as a 741 therapeutic target for COVID-19 (203; 204). induced coagulopathy (SIC), a type that is less severe and occurs earlier in patients than DIC (224). 776 However, during SARS-CoV-2 infection, SIC can progress to DIC, and the reasons are still unclear. 777 As discussed, the development of coagulation test abnormalities seen in SARS-CoV-2-infected 778 patients is likely a result of the profound inflammatory response (217). In patients with sepsis-induced 779 coagulopathy, the importance of evolution from adaptive hemostasis to pathologically-induced DIC 780 with multiorgan failure continues to be evaluated. is also present in SARS-CoV-2, suggesting that the mechanism is similar (228; 229 The DIC results from the activation of endothelial cells and monocytes by the cytokines released during 798 tissue injury, cytokine storm, and together with the expression of tissue factor, Willebrand factor (233), 799 factor VII, and fibrinogen (232). Another line of thought is that the origin of DIC in COVID-19 patients  800 is based on a decrease in urokinase-type plasminogen activator (u-PA), plasmin rescue for SARS-CoV-801 2 protein S cleavage (inefficient control of anticoagulant pathway), and increases in plasminogen 802 activator inhibitor 1 (PAI-1) and α2 antiplasmin (α2-AP) (234). Additionally, the cytokine storm and 803 CID seem to maintain a feedback relationship; some cytokines present in the cytokine storm increase 804 tissue factor expression storm (TNF, IL-1β, IL