Mucosal-Associated Invariant T Cells are not susceptible in vitro to SARS-CoV-2 infection but accumulate into the lungs of COVID-19 patients

Prolonged T cell lymphopenia is common in COVID-19, caused by SARS-CoV-2. While the mechanisms of lymphopenia during COVID-19 remain elusive, it is especially pronounced in a specialized innate-like T cell population called Mucosal Associated Invariant T cells (MAITs). MAITs has been suggested to express Angiotensin-Converting Enzyme 2 (ACE2), which is the well-known cellular receptor for SARS-CoV-2. However, it is still unclear if SARS-CoV-2 can infect or affect MAIT cells directly. In this study, we performed multicolor flow cytometry on peripheral blood mononuclear cells obtained from COVID-19 patients to assess the frequencies of CD8+Vα7.2+CD161+ MAIT subsets at acute and convalescent disease phases. The susceptibility of MAITs and T cells to direct exposure by SARS-CoV-2 was analysed using cells isolated from healthy donor buffy coats by viability assays, virus-specific RT-PCR, and flow cytometry. In situ lung immunofluorescence was used to evaluate retention of T cells, especially MAIT cells, in lung tissues during acute COVID-19. Our study confirms previous reports indicating that circulating MAITs are activated, and their frequency is declined in patients with acute SARS-CoV-2 infection, whereas an accumulation of MAITs and T cells was seen in the lung tissue of individuals with fatal COVID-19. However, despite a fraction of MAITs found to express ACE2, no evidence for the susceptibility of MAITs for direct infection or activation by SARS-CoV-2 particles was observed. Thus, their activation and decline in the circulation is most likely explained by indirect mechanisms involving other immune cells and cytokine-induced pro-inflammatory environment but not by direct exposure to viral particles at the infection site.

Stable Levels of Antibodies Against Unrelated Toxoid Vaccines After COVID-19: COVID-19 Infection Does Not Affect Toxoid Vaccine Antibody Levels

Background

Lymphopenia is common in COVID-19. This has raised concerns that COVID-19 could affect the immune system akin to measles infection, which causes immune amnesia and a reduction in protective antibodies.

Methods

We recruited COVID-19 patients (n = 59) in Helsinki, Finland, and collected plasma samples on 2 to 3 occasions during and after infection. We measured IgG antibodies to diphtheria toxin, tetanus toxoid, and pertussis toxin, along with total IgG, SARS-CoV-2 spike protein IgG, and neutralizing antibodies. We also surveyed the participants for up to 17 months for long-term impaired olfaction as a proxy for prolonged post-acute COVID-19 symptoms.

Results

No significant differences were found in the unrelated vaccine responses while the serological response against COVID-19 was appropriate. During the acute phase of the disease, the SARSCoV-2 IgG levels were lower in outpatients when compared to inpatients. SARS-CoV-2 serology kinetics matched expectations. In the acute phase, anti-tetanus and anti-diphtheria IgG levels were lower in patients with prolonged impaired olfaction during follow up than in those without.

Conclusions

We could not detect significant decline in overall humoral immunity during or after COVID-19 infection. In severe COVID-19, there appears to be a temporary decline in total IgG levels.

Real-life clinical sensitivity of SARS-CoV-2 RT-PCR test in symptomatic patients

BACKGROUND

Understanding the false negative rates of SARS-CoV-2 RT-PCR testing is pivotal for the management of the COVID-19 pandemic and it has implications for patient management. Our aim was to determine the real-life clinical sensitivity of SARS-CoV-2 RT-PCR.

METHODS

This population-based retrospective study was conducted in March-April 2020 in the Helsinki Capital Region, Finland. Adults who were clinically suspected of SARS-CoV-2 infection and underwent SARS-CoV-2 RT-PCR testing, with sufficient data in their medical records for grading of clinical suspicion were eligible. In addition to examining the first RT-PCR test of repeat-tested individuals, we also used high clinical suspicion for COVID-19 as the reference standard for calculating the sensitivity of SARS-CoV-2 RT-PCR.

RESULTS

All 1,194 inpatients (mean [SD] age, 63.2 [18.3] years; 45.2% women) admitted to COVID-19 cohort wards during the study period were included. The outpatient cohort of 1,814 individuals (mean [SD] age, 45.4 [17.2] years; 69.1% women) was sampled from epidemiological line lists by systematic quasi-random sampling. The sensitivity (95% CI) for laboratory confirmed cases (repeat-tested patients) was 85.7% (81.5-89.1%) inpatients; 95.5% (92.2-97.5%) outpatients, 89.9% (88.2-92.1%) all. When also patients that were graded as high suspicion but never tested positive were included in the denominator, the sensitivity (95% CI) was: 67.5% (62.9-71.9%) inpatients; 34.9% (31.4-38.5%) outpatients; 47.3% (44.4-50.3%) all.

CONCLUSIONS

The clinical sensitivity of SARS-CoV-2 RT-PCR testing was only moderate at best. The relatively high false negative rates of SARS-CoV-2 RT-PCR testing need to be accounted for in clinical decision making, epidemiological interpretations, and when using RT-PCR as a reference for other tests.

Factor H family proteins: on complement, microbes and human diseases

At present, the human Factor H protein family represents seven multidomain, multifunctional serum proteins. This group includes the complement and immune regulators Factor H, the Factor H-like protein 1 (FHL-1) and five Factor H-related proteins proteins (FHR-1, -2, -3, -4 and -5). Each is exclusively composed of individually folded protein domains, termed short consensus repeats (SCRs) or complement control modules. Structure-function analyses allowed the localization of the complement regulatory domain of Factor H and FHL-1 in the N-terminal region within SCRs 1-4. In addition, multiple binding sites for C3b, heparin and microbial surface proteins were localized in the N-terminus, within the middle region and also in the C-terminus of Factor H and FHL-1. Recent results show a central role for the C-terminus of Factor H, i.e. SCRs 19-20. These particular domains are conserved in all FHRs identified so far, include contact points for C3b, heparin and microbial surface proteins and represent a 'hot-spot' for gene mutations in patients that suffer from the Factor H-associated form of haemolytic uraemic syndrome.

Factor H and disease: a complement regulator affects vital body functions

Factor H is a multidomain and multifunctional protein. As a complement regulator factor H determines the fate of newly formed C3b and controls formation and stability of C3 convertases both in the fluid phase and on cell surfaces. In addition, this plasma protein displays functions outside complement control as it has been suggested to act as an adhesion protein, to be a ligand for the cellular integrin receptor CR3 (CD11b/CD18) and to display chemotactic activity. Genetic and pathophysiological analyses describe a role for factor H in vital body functions. Depletion or the absence of factor H due to genetic reasons leads to unrestricted C3 consumption. A reduced amount of factor H in plasma or mutations within the factor H gene may lead to glomerulonephritis (type II MPGN) or hemolytic uremic syndrome (HUS). Certain pathogenic organisms have been shown to evade complement attack by binding factor H from the host. Such specific factor H binding components have been demonstrated on the surface of microbes, e.g., Streptococcus pyogenes and Neisseria gonorrhoeae. Here, we summarize the current knowledge how abnormalities in function of the central complement regulator factor H are associated with human diseases.