In this study we found that the prevalence of DM in the COVID-19 group was 20% (19/95), and those severe patients had higher the prevalence of DM than those non-severe patients. As a comorbidities for COVID-19 patients,[8-9,20]the 20%(19/95) prevalence of DM in this cohort was consistent with one literature reported that 20%(8/41),higher than other literature reported that 13% (13/99). And the 36.67%(11/30) prevalence of DM in severe patients relative to 12.31%(8/65) in non-severe patients were not consistent with literature reported that no significant difference of DM prevalence was found between severe and non-severe patients.The reasons may be that there were 8 newly diagnosed DM cases after admission in this cohort , of them 3 non-severe cases and 5 severe cases. This discovery prompt that closely monitoring plasma glucose, testing glycated hemoglobin and performing glucose tolerance test for COVID-19 patients are necessary in order to find people with diabetes in time.
Further analysis we found that the severe rate in patients with COVID-19 and DM coexisting was lower than those Only COVID-9 and no DM, moreover DM was positively correlated with the viral negative conversion time and the disease severity, simultaneously it was an essential influencing factor for the disease severity, these findings was consistent with those literature reports that in patients with acute respiratory distress syndrome (SARS) and DM in 2003, the mortality rate ,the rate of check in the intensive care unit sand mechanical ventilation were 3.0~3.3 times of those no DM,the intensive care units rate of patients withH1N1 influenza and DM was 4.29 times of those no DM,in 2014a high-risk factor of the Middle East Respiratory Syndrome coronavirus infection severe cases was also DM.
We also found that overall and significantly reduced lymphocyte and subsets existed in COVID-19 patients, especially those with DM. Moreover the severe rate was the highest in those with DM, the prognosis was worst, and lymphocyte and subsets especially CD4+, CD8+ T and B cells was the lowest in those severe cases with DM, these findings was consistent with literature. But in the literature there was no hierarchical analysis performed between COVID-19 patients with and without DM .
Further analysis we found that factors negatively correlated the disease severity were lymphocyte and subsets, negatively correlated the prognosis was lymphocyte. The indicating factors for the disease severity were lymphocyte percentage value, CD4+ percentage value, age and DM, moreover for the prognosis included the disease severity, age and the virus negative conversion time.
In this study we also found that severe patients without DM were significantly older than non-severe patients without DM, this was consistent with that a poor prognosis was found in elderly COVID-19 patients.[8-9]Study found that between old and young mice CD4 T cell subsets were markedly different, exhausted three cell subsets, cytotoxic, and activated regulatory T cells (a Tregs) rarely appeared in young mice, but with age that gradually accumulated. Extreme anti-inflammatory and pro-inflammatory phenotypes of cytotoxic CD4 T cells and a Tregs were most unexpected. It was found that the relative frequency and total number of B cells will decrease with age. Plasma blasts, memory cell types and transitional B cells decrease in the older than 70 years group. Lymphocytes and their subsets (including NK (CD56 +) cells, B (CD19 +) cells and T (CD3 +) cells) were mainly responsible for regulating host immunity. T cells played an important role in promoting or maintaining inflammation by producing inflammatory cytokines.[22,25-28]A subtype of CD4+ effector T cells was activated Th1 cells, which triggered phagocyte-dependent inflammation and cell-mediated immunity through the production of Interferon-γ (IFN-γ), interleukin 2 (IL-2) and tumor necrosis factor β (TNF-β).In contrast, another subtype of CD4+ effector T cells, activated Th2 cells, modulated the antibody response by producing IL-13, IL-10, IL-9,IL-6, IL-5 and IL-4.Viral infection played a major role in disease progression by inducing indirect host immune response and direct cytopathic effects.[13,26]A fast and well-coordinated innate host immune response was the first line of defense against viral infections, but a dysregulated immune response could lead to excessive inflammation and even death.
Non-severe non-DM patients were younger than severe non-DM ones, and age was positively correlated with the prognosis, the viral negative conversion time and the disease severity, moreover age was an essential indicating factor for the prognosis and the disease severity, which was consistent with that the elderly had a poor prognosis.[8-9]However similar age was found between non-severe DM and severe DM patients, that is to say, age was not a factor in the disease severity for DM patients, which was inconsistent with those reports.[8-9]Type 2 diabetes mellitus (T2DM) is a systemic chronic low-grade inflammatory disease. The function of specific T lymphocyte subsets (including T regulatory (Treg) cells) has changed, leading to the following hypothesis: partial inflammation exacerbate T2D autoimmunity.T cells play an important role in promoting or maintaining insulin resistance and inflammation by inducing the production of pro-inflammatory cytokines in metabolic organs (such as pancreas, muscle, adipose tissue and liver).[28,30-32] In adipose tissue the major inflammatory cells was macrophages.[ 28,30-32]Proinflammatory M1 macrophages releasing proinflammatory cytokines such as IL-6, TNF-a and IL-1contribute to the local and systemic inflammation.On the contrary, anti-inflammatory M2 macrophages secreting IL-10inhibit the activity of most pro-inflammatory cell types including M1 macrophages.IL-10 by interacting with the p38/MAPK pathway suppress TNF-a.Th1 cells producing TNF-a,IL-2,IFN-γpromote M1 polarization and enhance its pro-inflammatory functions. In contrast, Th2 cells skew the differentiation of macrophage towards M2 by producing anti-inflammatory IL-4, and IL-13. [28,30-32] Therefore, Th1 and Th2 responses, which are closely related to M1/M2 polarization, may also have a critical role in T2DM. [ 28,30-32]
Previous research found that in COVID-19 patient higher expression of proinflammatory cytokines and chemokines, especially in the severe cases, the consumption of CD4+ and CD8+ T cells, and the decrease of regulatory T cells, might result in aggravated inflammatory responses, the production of cytokine storm and make damaged tissue worse. Maybe lower number of lymphocytes suggested a role for dysregulated immune responses in COVID-19 pathogenesis.[13-14]Our research discoveries suggested that the coexistence of viral infection and DM result in more dysregulated host immune responses thus worsen the already aggravated inflammatory process, more susceptible to bacterial infections, more severe organ damage and worse prognosis, simultaneously the coexistence of viral infection and DM can reduce or delay antibody production by decreasing B(CD19+) count level and percentage value, thereby delaying the removal of the virus, worsening prognosis.
In this work, we evaluated that the characteristics of lymphocyte subsets and its relationship with the disease progression in COVID-19 patients with or without DM, and found that the coronavirus disease 2019 (COVID-19) patients had overall reduced lymphocyte and subsets. Partial decreased lymphocyte subsets, age and DM as factors closely related with the disease severity, the viral negative conversion time and the prognosis. Our study demonstrated several novel information that the coexistence of viral infection and DM result in more dysregulated host immune responses thus worsen the already aggravated inflammatory process, more susceptible to bacterial infections, more severe organ damage and worse prognosis, simultaneously the coexistence of viral infection and DM can reduce or delay antibody production, thereby delaying the removal of the virus, worsen prognosis. Combination immunomodulatory therapy based on comprehensive treatment might improve prognosis of COVID-19 patients, especially those severe cases or with DM.
Our study had several limitations. It was a retrospective, single center and small sample study. Despite that, our study demonstrated several novel information that the coexistence of viral infection and DM result in more dysregulated host immune responses thus worsen the already aggravated inflammatory process, more susceptible to bacterial infections, more severe organ damage and worse prognosis, simultaneously the coexistence of viral infection and DM can reduce or delay antibody production, thereby delaying the removal of the virus, worsen prognosis.