Month: May 2021

A group from Vrije Universiteit Amsterdam, Netherlands has studied alterations in the dendritic cells (DCs) signal paths after α2-3Sia binding.
https://www.frontiersin.org/articles/10.3389/fimmu.2021.673454/full

DCs possess the extraordinary capacity to recognize various pathogens with its pattern recognition receptors (PPRs) and present those antigens with MHC to tell the information to T-cells.
Sialic acids are increasingly attracting attention with their role in the immune regulation of cancer. During cancer progression, tumor cells often highly increase their sialic acid expression to create an immunosuppressive tumor microenvironment. Sialic acids are also advantageous for pathogens to evade from immune attacks. Bacteria obtain sialic acids by de novo synthesis or from an environmental source, and thereby can hide and escape from immune surveillance.

Authors analyzed alterations in the DC phosphoproteins, Kinase signatures, and JAK-STAT signaling pathway due to α2-3Sia stimulation in the presence of Lipopolysaccharide (LPS). LPS is often used as a model antigen (as an endotoxin) to activate immunity.

Overview of the result was summarized as follows.
Phosphorylation was enhanced upon α2-3Sia stimulation, while simultaneous α2-3sia and LPS stimulation resulted in less phosphorylation, indicating that recognition of a2-3Sia by DC alters TLR 4 triggering and DC signaling. α2-3Sia stimulated DCs compared to control with simultaneous α2-3sia and LPS stimulation showed decreased scoring of kinases ERK, AKT1, PKCB, GSK3, PKCD, PAK1, PKA, GSK3, GRK, IκB, and RAF1, and those affected kinase signatures were involved in the chemokine signal pathway. α2-3sia stimulation affected the JAK-STAT signaling by lowering the phosphorylation status of STAT3 and STAT5A.

Although the things are so complicated, these changes result in downregulation of IL-12 (inflammatory cytokine) pathway and inversely upregulation of IL-10 (anti-inflammatory cytokine) pathway, leading allover features to the direction of suppressing inflammation.
 

A group from IRCCS Azienda Ospedaliero-Universitaria di Bologna, Italy has reported on differences in lung microbiome between COVID-19 patients and COVID-19 negative persons.
https://www.nature.com/articles/s41598-021-89516-6

Several indexes have been developed to discuss about similarity among groups and characteristics of each group.
Similarity Percentage analysis highlighted that the lung microbiome of COVID-19 patients was characterized by a higher relative abundance of Pseudomonas spp. compared to COVID-19-negative persons. On the other hand, the lung microbiome of COVID-19-negative persons was mainly characterized by the enrichment of lung commensal bacteria (such as Haemophilus influenzae, Veillonella dispar, Granulicatella spp., Porphyromonas spp., and Streptococcus spp).

The linear discriminant analysis (LDA) highlighted that the lung microbiome of COVID-19 patients was characterized by the presence of Pseudomonas alcaligenes, Sphingobacterium spp., Clostridium hiranonis, Acinetobacter schindleri, Enterobacteriaceae of unknown genus and Acinetobacter spp.

A common feature between these two analysis indexes was Pseudimonas spp. This means that enrichment of opportunistic gram-negative pathogens frequently associated with multidrug resistance increase in COVID-19 patients and the lung commensal bacteria decrease inversely.

A group from Hokkaido University, etc. has reported on changes in the expression levels of ACE2 and TMPRSS2 with agonists for Toll-like receptors (TLRs) and with Fluticasone Propionate (FP)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8107375/

It is said that SARS-CoV-2 cell entry depends on two proteins present on the surface of host cells, angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2). Authors has investigated effects of activation of innate immune signal path onto the expression levels of ACE2 and TMPRSS2, and also if there is any effect of FP administration on that.

As sample cells, primary human nasal epithelial cells (HNECs) were collected from the nasal mucosa. HNECs were stimulated by Poly(I:C), which is a double-stranded RNA (dsRNA) often used as a agonist for TLRs in a model of viral infection.

ACE2 and TMPRSS2 protein expression levels were evaluated by using immunofluorescent analysis. The ACE2 intensity in HNECs was significantly promoted by Poly(I:C) (a 2.884±0.505-fold change vs. untreated cells, p=0.003), but there were no significate changes in the TMPRSS2 expression levels. And, this Poly(I:C)-induced change in ACE2 was significantly suppressed by FP (a 0.405±0.312-fold change vs. Poly(I:C)-treated cells, p=0.044).

Further studies are required to evaluate whether FP suppresses SARS-CoV-2 viral cell entry in vivo.

A group from Stanford University School of Medicine, etc. has reported about passive immunity of infants born to mothers infected with SARS-CoV-2.
https://pubmed.ncbi.nlm.nih.gov/33972953/

An important aspect of immunity against infectious pathogens in young infants relies on effective maternal antibody production, transfer of maternal antibodies across the placenta to the fetus, and persistence of passive immunity in the infant. Authors have investigated SARS-CoV-2 antibody transplacental transfer ratios with respect to the timing of maternal infection during gestation, antibody response to SARS-CoV-2 infection in the newborns, and persistence of passively- and actively-acquired SARS-CoV-2 antibodies in infants.

The study enrolled 145 mothers with SARS-CoV-2 infection and 147 of their infants. There was a significant positive correlation between IgG levels in the 125 paired maternal and cord blood samples (Rs=0.93, p<0·0001). Transplacental IgG transfer ratios were calculated in 77 IgG positive mother-infant dyads, and the median transfer ratio was 1.0 (95% CI 0.86-1.09). The transfer ratio was significantly higher in the mothers who were severe-critically symptomatic (n=4) compared to mothers who were asymptomatic (n=23) (1.6 vs. 1.0, p=0.003) or mild-moderately symptomatic (n=50) (1.6 vs. 0.9, p=0.002). The transfer ratios based on time elapsed from the first maternal positive PCR to delivery were 0.6 (<60 days, n=22), 1.2 (60-180 days, n=27), and 0.9 (>180 days, n=5). These studies demonstrate that cross-placental SARS-CoV-2 IgG transfer occurs throughout gestation, and a higher transfer efficiency is achieved when infection onset is more than two months prior to delivery. These findings have important implications in determining optimal timing of vaccination in pregnant mothers and infants. 

A group from University of Alberta, Canada, etc. has reported that Gal-9 could be a quite good diagnostic marker for COVID-19.
https://mbio.asm.org/content/12/3/e00384-21.long

Innate immune cells recognize and respond to a wide variety of pathogens. For example, activated macrophages/monocytes secrete excessive amounts of cytokines including IFN-γ, IL-1, IL-6, TNF-α, and IL-18. Similarly, neutrophils produce neutrophil extracellular traps and NK cells prolong the antigenic stimulation due to diminished/skewed cytolytic functions, both of which can amplify cytokine production. Overall, it appears that the viral burden, accompanied by the dysregulated innate immune response due to underlying disease, and aging may ignite the cytokine storm.

Galectins are involved in many biological functions such as development, signal transduction, and immune responses. This study was performed in a cohort of 120 SARS-CoV-2-infected individuals and 59 healthy controls (HCs) to understand how galectins, especially focusing on Gal-9, could be positioned in COVID-19.

Significantly higher levels of Gal-9 in the plasma of COVID-19 patients were observed comparing to HCs (ranging between 0 and 2,042 pg/ml). The plasma Gal-9 concentrations were substantially greater in severe cases (ranging between 1,950 and 125,510 pg/ml) comparing to those with mild/moderate cases (ranging between 1,000 and 83,717 pg/ml). From a ROC curve, quite high specificity/sensitivity (95%) to discriminate COVID-19 from either HCs or patients with HIV and virus-associated cancers with a cutoff value of 2,042 pg/ml. It is quite interesting to know that the plasma Gal-9 concentration in COVID-19 patients surpasses the detectable levels reported in other conditions such as HIV, dengue fever, influenza, and virus-associated solid tumors.

Through a series of experiments to identify what cells secrete Gal-9 and to understand how Gal-9 activates innate immune cells contributing to the cytokine storm, the following model was proposed as a conclusion. The damaged lung epithelial cells following SARS-CoV-2 infection release Gal-9, which activates alveolar macrophages, resulting in the secretion of proinflammatory cytokines and Gal-9 from the activated or apoptotic cells. Subsequently, Gal-9 activates monocytes and other immune cells, orchestrating another wave of proinflammatory cytokines and Gal-9 release, and exacerbates the cytokine storm further.

A group from National Institute of Metrology, Beijing, China, etc. has reported characteristics of antibody responses in COVID-19 asymptomatic individuals.
https://www.nature.com/articles/s41392-021-00596-2

Over 40% of individuals undergo asymptomatic infection without showing any symptoms. It is considered that these asymptomatic individuals can efficiently transmit viral infection accounting for more than 30% of virus infection

A total of 143 asymptomatic individuals with SARS-COV-2 were recruited in the study. The viral loads of SARS-CoV-2 based on N gene in saliva peaked at Day 9 of the first detection (315.1 copies/mL, 95% CI 238.1–417.1), followed by gradual decrease and from Day 21 detection was below the cut-off value (102 copies/mL) in a figure below. The positive rate of SARS-CoV-2 detection showed the same trend with the viral loads.

It is found that the antibody responses are short-lived lasting only about 69 days.

A group from University of Campania L. Vanvitelli, Naples, Italy has reported the relationship between expression levels of ACE2 and increased risks of SARS-CoV-2 infection to cardiomyocytes due to Diabetes Mellitus
https://cardiab.biomedcentral.com/articles/10.1186/s12933-021-01286-7

Comparing diabetes mellitus (DM) patients and healthy individuals, the expression levels of ACE2 and TMPRSS2 were higher in DM patients than non-DM individuals significantly (see a figure below).
Further, comparing COVID-19 patients and non-COVID-19 individuals, the expression levels of ACE2 and TMPRSS2 were much higher in COVID-19 patients.
As a result, the increased risk of SARS-CoV-2 infection in DM patients would be related to the increased expression levels of ACE2.

A group from Universidade Federal do Rio de Janeiro, etc. has reported the relationship among the expression levels of ACE2, TMPRSS2, and severity of COVID-19.
https://www.nature.com/articles/s41598-021-88944-8

ACE2 and TMPRSS2 are known to be key players on SARS-CoV-2 entry into host cells. However, it is still unclear whether expression levels of these factors could reflect disease severity. The angiotensin-converting enzyme 2 (ACE2) has been described as the entry receptor for SARS-CoV-2 and the transmembrane serine protease 2 (TMPRSS2) as an important priming enzyme required during this process.

A case–control study was carried out including 213 individuals with SARS-CoV-2 infection confirmed by RT-qPCR in nasopharyngeal samples.
Expression of both genes of ACE2 and TMPRSS2 was positively correlated to age (r = 0.20; p = 0.03 and r = 0.21; p = 0.01 for ACE2 and TMPRSS2, respectively), while no association with sex was observed.
Transcription levels of ACE2 were significantly lower among cases than in controls, while similar levels of TMPRSS2 were observed in both groups. However, TMPRSS2/ACE2 ratios were significantly higher among cases than those of controls. From blog admin’s point of view, It is interesting but quite difficult to understand that the expression levels of ACE2 showed a protective effect for the infection, no significant association between the levels of TMPRSS2 and the infection, but TMPRSS2/ACE2 ratio could be a risk factor on COVID-19 severity, suggesting that other infection paths would be behind the ACE2/TMPRSS2 infection path.