Discussion
The world observed the SARS outbreak in 2002 and 2003, as well as the MERS spread in 2011, both of which were caused by coronaviruses. Another coronavirus that causes respiratory disease was found in Wuhan, China, near the end of 2019, and was formally designated COVID-19. (13) This infection has advanced to other regions of China and other countries since late 2019, and its transmission rate, fatality rate, and clinical manifestations have all been determined. However, it will take several months, if not years, to completely understand all of the disease’s qualities and characteristics, including its genesis, symptoms, and the patient’s immunological response to this infection. The production of high levels of cytokines such as IL-1, IL-2, IL-4, IL-6, IL-10, IL-17 , TNF- alpha and IFN-gamma in infected patients, is involved in the underlying pathophysiology of the present COVID-19 pandemic,(13,14) while specific immunoglobulins IgG and IgM (15), cholesterol levels (16) CRP (17) and lymphocyte counts (18) are implicated in the diagnosis and progression of the disease.
In our study there was a significant relationship between lymphocyte count and all parameters including lymphocyte counts, CRP (P=0.02), IL10 (P=0.0), and cholesterol levels in all groups. (19)This is in accordance with other studies that have indicated that lymphocyte counts are an important indicator of COVID-19 and disease progression. (19)
In our study lymphocyte counts in unvaccinated patients 50% had higher lymphocyte counts while in vaccinated patients only 70% had lymphocyte counts higher than normal. Lymphocyte counts in all control groups were normal. In our study since the lymphocyte count measurement was made 2-3 weeks after infection only 15.4% of the patients had lower than normal counts. Many clinical studies indicated a decrease in lymphocyte counts which was became a standard diagnosis parameter for COVID. These studies show that severe disease is specifically identified by an increased neutrophil count is among the key results which is combined with a lower lymphocyte count (therefore the neutrophil to lymphocyte ratio has increased significantly). (20)
In unvaccinated patients 65% had higher cholesterol levels, while in vaccinated patients only 15% had cholesterol levels higher than normal. Cholesterol levels in all control groups were normal. Our results show that 65% of unvaccinated patients in this study have higher cholesterol levels which might be a reason for the higher susceptibility of this group and the correlation between the studied cytokines and cholesterol levels is significant (Table1) which indicates a meaningful relationship in COVID-19 patients and warrants further investigation. (20)
In the unvaccinated patient group 90% had CRP levels significantly higher than normal (P<0.05) while in the vaccinated patients group 80% had higher than normal CRP levels. (Figure 5) CRP levels in all control groups were normal. Our results show that higher CRP levels are a reliable indicator for COVID-19 diagnosis in most cases and this result is in accordance with other studies. (21)
In our study 100% of unvaccinated patients and 90% of vaccinated patients had significantly higher than normal IL6 levels after the infection. (Figure 2) IL6 in all control groups were normal. Our findings correlated with many other clinical studies that indicated that IL6 is a major inflammatory factor in COVID-19 and plays a key role in the events leading to a cytokine storm. (22) High levels of IL-6, a pro-inflammatory cytokine, are known to inhibit NK cell function and have also been linked to an impaired lytic activity. Disease progression symptoms such as elevated body temperature, elevations in inflammatory indicators such as CRP and serum ferritin, and advanced chest computed tomography imaging were related to higher IL-6 levels that decreased during recovery in COVID-19 patients. This link between IL-6 and pulmonary diseases has previously been established in individuals with radiation-induced pneumonia or severe alveolitis. (23) In our work, also the levels of IL6 after infection (first day of positive PCR) was higher than after recovery. (Figure 2)
In our work, 95% of unvaccinated patients and 100% of the vaccinated patients had statistically significant higher than normal levels of IL10 after the infection as compared to healthy controls. IL10 levels in all control groups were within the normal range. (Figure 3 ) These results indicate that an increase in IL-10 during COVID-19 is a hallmark of both vaccinated and unvaccinated patients. IL-10, on the other hand, is an anti-inflammatory cytokine that has been observed to be increased in individuals with severe COVID-19. T-cell stress was also observed to be associated with IL-6, IL-10, and TNF-levels in COVID-19 patients. IL-10 is a key molecule with the main role of suppressing the inflammatory process. IL-10 has also been associated with T-cell immune activation and non-responsiveness in anti-tumor cell responses, in addition to viral infection. Studies show that an antibody against IL-10 or its receptor or genetic ablation of IL-10 resulted in the eradication of viral or bacterial pathogen attacks. Thus, higher IL-10 levels in severe COVID-19 patients were first attributed to a negative feedback mechanism, including its anti-inflammatory actions. (23)
In our study 95% of unvaccinated patients and 90% of vaccinated patients had significantly higher IL17 after the infection. IL17 in all control groups were normal. (Figure 4) IL-17 specifically boosts proinflammatory, but not antiviral gene expression in human cells infected with respiratory viruses by stimulating non immune cells (fibroblasts and epithelial cells) to produce increased amounts of proinflammatory cytokines and chemokines in response to viral infections that attract other immune cell types (for example, neutrophils) which can lead to increased morbidity while simultaneously remaining inefficient in inhibiting the spread of the pathogen. Th17 cells appear to play a major role in COVID-19 disease, not only by stimulating the cytokine pathway, but also by promoting Th2 responses, blocking Th1 differentiation, and inhibiting regulatory T cells. (24)
Also correlation studies in our work show significant correlation between CRP, IL-6, IL-10 and IL-17 (Figure 6,7) indicating that common signaling pathways may be involved between inflammatory factors and these cytokines as other work have indicated.(25)
In conclusion, it may be inferred that while research on the COVID-19 pandemic at the global level is ongoing our clinical studies have displayed a meaningful relationship between cholesterol levels, IgM/ IgG detection, CRP levels and IL-6, IL-10 and IL-17 pointing to the importance of these immune and metabolic factors for diagnosis and therapy for COVID-19 patients. Further studies on the long term consequences of COVID on life quality parameters are also underway and will shed light on the ambiguous dimensions of the Long COVID phenomena. This study has been performed for the first time in Iraq , Wasit province and will serve as an important standard for future basic and clinical research in this field.