Genetic clues to COVID-19 severity: Exploring the stromal cell-derived factor 1/CXCL12 rs2839693 polymorphism in BMC in adult Egyptians Infectious Diseases

Since the tragedy of COVID-19 first emerged, numerous investigations have been conducted to understand the mechanisms of the disease and determine the reasons for differences in symptoms among patients. Due to the importance of chemokines and their receptors in the pathogenesis of cytokine storm and ARDS, they are one of the most important elements to study in this context. Therefore, by fully understanding the characteristics of chemokines and their receptors, it may be possible to predict the outcome of COVID-19. Therefore, we propose that CXCL12 may affect the outcome and severity of COVID-19.

Our current study examined 156 mild or moderate and 144 severe or critical COVID-19 patients at Assiut University Quarantine Hospital from a cross-sectional perspective.

The majority of our participants were vaccinated (69.3% compared with 30.7% of unvaccinated patients) and non-smokers (60.7% compared with 39.3% of smokers). Hypertension and diabetes were the most common comorbidities, accounting for 35.7% and 26.0% of patients respectively; kidney disease, heart disease and thyroid disease were less common. These findings are consistent with a study by Petrakis et al., who reported that the most common comorbidities were hypertension in 38.4% of patients and diabetes in 20.9% of patients (19).

Furthermore, in terms of clinical manifestations in the study group, the main clinical symptoms of COVID-19 were fatigue (55.0%), dry cough (53.7%), and dyspnea (48.0%), and these findings were similar to those of Rodriguez-Morales et al. ., reported that the main clinical symptoms of COVID-19 were cough (57.6) and dyspnea (45.6); in sharp contrast to our results of fatigue (29.4%) (20).

Regarding laboratory evaluation, in most cases the lymphocyte value 185 (61.7%) was usually in the range (1.0–4.0 × 109/L), whereas lymphopenia was observed in 84 (28.0%) patients. Ferritin and CRP were elevated by 200 (66.7%) and 250 (83.3%) respectively in most cases. In addition, D-dimer was elevated in 180 (60.0%) of our cases. Our results are consistent with those of Kadhim et al. and Smail et al., who observed lymphopenia and elevated CRP, ferritin, and D-dimer in COVID-19 patients (21, 22).

Bilateral GGO was the most common CT abnormality 205 (68.3%). Pulmonary consolidation is another common CT feature in COVID-19 patients 107 (35.7%). These findings are similar to a previous meta-analysis study of 13 studies, which concluded that GGO is the predominant CT finding in COVID-19 patients, followed by consolidation (23).

The majority of our participants received antibiotics, 288 (96.0%) patients; 323 (77.3%) and 176 (58.7) patients received antiviral therapy and glucocorticoid therapy, respectively. 227 patients (75.7%) required oxygen therapy: 78 (26.0%) with nasal cannula, 150 (50.0%) with mask oxygen, and 18 (6.0%) with invasive mechanical ventilation. Langford et al.’s meta-analysis study on the use of antibiotics for COVID-19 found that the frequency of antibiotic treatment was 74.6% (24).

The average length of stay was 7.0 days. These findings are consistent with Alwafi et al., who reported a mean length of stay of 6.0 days (25). Median ICU length of stay was 7.0 days. In contrast to our results, López-Cheda et al. reported a median ICU length of stay of 14.0 days (26).

Median recovery time was 15.0 days. Our data are consistent with SeyedAlinaghi et al., who found a median recovery time of 13.5 days (27). Regarding mortality, our data shows that 39 people (13.0%) died. These results are consistent with data collected from 20 Italian regions by Immovilli et al., which showed mortality rates ranging from 3.1% to 16.7% (28).

The TT genotype and T allele frequencies of CXCL12 rs2839693 were significantly different between mild and moderate patients and severe and critical patients. The frequency of TT genotype and T allele in the severe or critical group was higher than that in the mild or moderate group, which may indicate the role of CXCL12 rs2839693 in the pathogenesis and severity of COVID-19. Patients with the TT genotype or T allele are at increased risk of developing severe or critical disease rather than mild or moderate disease. Our results are consistent with Mohamed et al., who reported no difference in the frequency of the TT genotype or T allele of CXCL12 rs2839693 in ITP patients and controls and no correlation between this SNP and disease severity (13).

Normal CXCL12 is the only ligand that can bind to the CXCR4 receptor. SARS-CoV-2 is a competitor of CXCL12 at the CXCR4 receptor. The severe condition of patients with TT genotype may be due to the influence of CXCL12 polymorphism, which leads to its dysfunction. Therefore, it clears the way for SARS-CoV-2 to bind to CXCR4 as a coreceptor, leading to increased viral load and disease severity.

CXCL12 has anti-inflammatory effects, for example by increasing angiogenesis and tissue repair. Prolonged CXCL12 activity may not only improve leukocyte chemotaxis, which is beneficial, but may also worsen the chronic inflammation found in COVID-19 (29). CXCL12 expression increases with autoimmune diseases. CXCL12 levels are elevated in individuals with a range of inflammatory diseases, suggesting a role for CXCL12 in autoimmunity (30).

The expression of CXCL12 is elevated in fibroblasts from severe COVID-19 patients, which may help attract immune cells with CXCR4 receptors, such as macrophages, T cells, and NK cells (31). Previous research found that severe COVID-19 patients hospitalized in intensive care units had higher levels of CXCL12 in the blood compared with hospitalized patients with mild to moderate disease and/or healthy controls (32).

CXCL12 gene polymorphisms may affect the regulation of ACE2, the receptor used by the SARS-CoV-2 virus to enter human cells. Alterations in ACE2 expression or function may affect viral entry and disease progression. ACE2 expression levels are much higher in patients with severe COVID-19, making the virus more aggressive (33).

Genetic polymorphisms in CXCL12 may lead to differences in immune cell recruitment and activation, which may affect the immune response to the virus and the development of severe COVID-19. Efficient hematopoiesis, T cell and memory B cell homing to lymph nodes and monocyte recruitment are dependent on CXCL12 (CXCR4 ligand). Several viruses exploit inhibition of this axis to reduce the number of circulating immune cells and increase their own proliferation rate (32).

CXCL12 polymorphisms may affect the ability to clear the virus from the body, thereby affecting the duration and severity of COVID-19. Cellular clearance of the virus depends on the production of virus-specific antibodies that prevent free viral particles from entering uninfected cells, either by protein recruitment or by phagocytosis by immune cells containing the CXCL12 receptor, such as macrophages and neutrophils. Eliminate to condition the virus to inactivate it. They also inactivate or initiate killing of infected cells by activating the complement cascade and antibody-mediated cytotoxicity processes, which are critical (34) .

Eliminating SARS-CoV-2 could shorten recovery time or reduce disease severity. According to Cheng, F. et al., removal of viral shedding after viral clearance in patients will also help reduce viral transmission (35).

Wang et al. found that patients with CXCL12 rs2839693 were associated with increased susceptibility to sepsis, which is consistent with our data (36). Zhang et al. conducted a study on 597 patients with coronary artery disease and the results showed that CXCL12 rs2839693 TT is associated with an increased risk of coronary artery disease in men (12).

Multivariable logistic regression analysis for genotypes of clinical COVID19 showed that combined genotype CT + TT could serve as an independent predictor of severe or critical clinical status of COVID 19.

According to the CXCL12 rs2839693 genotype, our results showed no significant differences between genotypes in terms of age, sex, vaccination, and comorbid diseases. On the other hand, regarding symptoms, our results showed a significant correlation between genotype distribution and dyspnea, vomiting, and dysarthria in COVID-19 patients. Dyspnea was more prevalent in the CT + TT combination and the TT genotype than in the CC and CT, CC genotypes. Vomiting and dysarthria were significantly more common in the TT genotype compared with the CT and CC genotypes. Regarding the clinical course of the disease, we found that severe or critical illness associated with CT + TT and TT combinations was more common in the CT + TT and TT combination genotypes than in the CC and CT, CC genotypes, respectively.

Based on laboratory assessment, our results showed significant differences in CRP, D-dimer, and ferritin between genotypes. Compared with CC and CC, CT genotypes, CRP and D-dimer were significantly increased in CT + TT combination and TT; compared with CC and CT genotypes, ferritin was significantly increased in TT genotype. Furthermore, no significant differences were found between the 3 genotypes in terms of lymphocyte count, white blood cell count, and CT results.

Regarding treatment, significant differences were detected between genotypes with clexane as treatment; Clexane was more common in the TT genotype than in the CC and CT genotypes. There were significant differences in the number of patients not requiring oxygen therapy between genotypes, with the CC genotype being more common compared with the CT + CC and TT genotype combinations. Nasal intubation and invasive mechanical ventilation were more prevalent in the TT and combined CT + TT genotypes, respectively, compared with the combined CC, CT, and CC genotypes. Patients with the CT + TT genotype more commonly used mask oxygen than patients with the CC genotype.

The number of patients requiring home management was significantly higher with the CC genotype compared with the CT + TT combination and the TT genotype. Patients with the CT + TT combination and TT genotype had significantly higher ICU hospitalization requirements compared with CC and CC, CT genotypes. Regarding mortality, our results showed that the CT + TT combination and TT genotype had significantly higher mortality compared with CC and CC, CT, respectively. Patients with the TT genotype had a longer hospital stay than patients with the CC genotype.

Our findings may provide new insights into the different factors that influence disease severity and the mechanisms of cytokine storm syndrome, which may influence COVID-19 outcomes and treatment strategies.

We encountered two limitations while conducting this study. First, the number of patients is limited due to difficulties in collecting samples from critical cases, asymptomatic cases, or recovered cases. Second, some cases were excluded from the study due to negative symptoms or some comorbidities that were not suitable for the study.


This study recommends investigating other SNPs in the CXCL12 gene and their relationship with COVID-19 pathogenicity and severity. It also recommends expanding the study patient population to better understand the impact of CXCL12 gene variants in COVID-19 patients.

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