Circulating NK cells establish tissue residency upon acute infection of skin and mediate accelerated effector responses to secondary infection.

Natural killer (NK) cells are present in the circulation and can also be found residing in tissues, and these populations exhibit distinct developmental requirements and are thought to differ in terms of ontogeny. Here, we investigate whether circulating conventional NK (cNK) cells can develop into long-lived tissue-resident NK (trNK) cells following acute infections. We found that viral and bacterial infections of the skin triggered the recruitment of cNK cells and their differentiation into Tcf1hiCD69hi trNK cells that share transcriptional similarity with CD56brightTCF1hi NK cells in human tissues. Skin trNK cells arose from interferon (IFN)-γ-producing effector cells and required restricted expression of the transcriptional regulator Blimp1 to optimize Tcf1-dependent trNK cell formation. Upon secondary infection, trNK cells rapidly gained effector function and mediated an accelerated NK cell response. Thus, cNK cells redistribute and permanently position at sites of previous infection via a mechanism promoting tissue residency that is distinct from Hobit-dependent developmental paths of NK cells and ILC1 seeding tissues during ontogeny.

Simultaneous Increases in Intracellular Sodium and Tonicity Boost Antimicrobial Activity of Macrophages.

Inflamed and infected tissues can display increased local sodium (Na+) levels, which can have various effects on immune cells. In macrophages, high salt (HS) leads to a Na+/Ca2+-exchanger 1 (NCX1)-dependent increase in intracellular Na+ levels. This results in augmented osmoprotective signaling and enhanced proinflammatory activation, such as enhanced expression of type 2 nitric oxide synthase and antimicrobial function. In this study, the role of elevated intracellular Na+ levels in macrophages was investigated. Therefore, the Na+/K+-ATPase (NKA) was pharmacologically inhibited with two cardiac glycosides (CGs), ouabain (OUA) and digoxin (DIG), to raise intracellular Na+ without increasing extracellular Na+ levels. Exposure to HS conditions and treatment with both inhibitors resulted in intracellular Na+ accumulation and subsequent phosphorylation of p38/MAPK. The CGs had different effects on intracellular Ca2+ and K+ compared to HS stimulation. Moreover, the osmoprotective transcription factor nuclear factor of activated T cells 5 (NFAT5) was not upregulated on RNA and protein levels upon OUA and DIG treatment. Accordingly, OUA and DIG did not boost nitric oxide (NO) production and showed heterogeneous effects toward eliminating intracellular bacteria. While HS environments cause hypertonic stress and ionic perturbations, cardiac glycosides only induce the latter. Cotreatment of macrophages with OUA and non-ionic osmolyte mannitol (MAN) partially mimicked the HS-boosted antimicrobial macrophage activity. These findings suggest that intracellular Na+ accumulation and hypertonic stress are required but not sufficient to mimic boosted macrophage function induced by increased extracellular sodium availability.

Multistep screening and selection of COVID-19 convalescent plasma donors at the early stage of the SARS-CoV-2 pandemic: A retrospective analysis.

Background and Aims: The COVID-19 pandemic reached Bavaria in February 2020. Almost simultaneously, Chinese physicians published reports on the first successful treatments with plasma from COVID-19 convalescent donors. With these silver linings on the horizon, we decided to establish the manufacturing of anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody-containing plasma from COVID-19 convalescent donors at our site. Here we describe our donor selection process, built from the ground up, which enabled us to cope with the immense resonance after our social media call for donors. Methods: As a first step, we created a specific questionnaire for telephone interviews applied by trained students to filter the wave of callers interested in plasma donation. Afterward, the medical staff evaluated the hotline questionnaires and chose eligible donors to be invited for on-site donor evaluation. Data documentation was performed with MS Excel, and statistical analyses were calculated with GraphPad Prism 8. A quantitative in-house ELISA was used to detect anti-SARS-CoV-2 antibodies and determine specific titers. Results: Out of 1465 calls from potential plasma donors, we could register 420 persons with a completed questionnaire. Evaluation of questionnaires identified 222 of 420 persons as eligible for donation, and 55 were directly asked for on-site donor qualification. Subsequently, as anti-SARS-CoV-2 antibody titers ≥1:800 were required, we invited 89 of 222 potential donors for an antibody screening. This procedure resulted in another 28 potential donors for an on-site evaluation. Finally, 12 donors qualified with a titer of 1:400 and 24 with ≥1:800. Conclusion: Identifying suitable COVID-19 convalescent plasma donors was expected to be highly time-consuming. Implementing a screening procedure with our hotline questionnaire helped us streamline the donor selection process and reduce the workload for the staff. We propose combining the described selection process with the later introduced on-site antibody screening as an effective strategy.

High Na+ Environments Impair Phagocyte Oxidase-Dependent Antibacterial Activity of Neutrophils.

Infection and inflammation can augment local Na+ abundance. These increases in local Na+ levels boost proinflammatory and antimicrobial macrophage activity and can favor polarization of T cells towards a proinflammatory Th17 phenotype. Although neutrophils play an important role in fighting intruding invaders, the impact of increased Na+ on the antimicrobial activity of neutrophils remains elusive. Here we show that, in neutrophils, increases in Na+ (high salt, HS) impair the ability of human and murine neutrophils to eliminate Escherichia coli and Staphylococcus aureus. High salt caused reduced spontaneous movement, degranulation and impaired production of reactive oxygen species (ROS) while leaving neutrophil viability unchanged. High salt enhanced the activity of the p38 mitogen-activated protein kinase (p38/MAPK) and increased the interleukin (IL)-8 release in a p38/MAPK-dependent manner. Whereas inhibition of p38/MAPK did not result in improved neutrophil defense, pharmacological blockade of the phagocyte oxidase (PHOX) or its genetic ablation mimicked the impaired antimicrobial activity detected under high salt conditions. Stimulation of neutrophils with phorbol-12-myristate-13-acetate (PMA) overcame high salt-induced impairment in ROS production and restored antimicrobial activity of neutrophils. Hence, we conclude that high salt-impaired PHOX activity results in diminished antimicrobial activity. Our findings suggest that increases in local Na+ represent an ionic checkpoint that prevents excessive ROS production of neutrophils, which decreases their antimicrobial potential and could potentially curtail ROS-mediated tissue damage.

Manufacturing of convalescent plasma of COVID-19 patients: Aspects of quality.

The ongoing coronavirus disease 2019 (COVID-19) pandemic emerged in December 2019. Convalescent plasma represents a promising COVID-19 treatment. Here, we report on the manufacturing of a plasma-based product containing antibodies specific to SARS-CoV-2 obtained from recently recovered COVID-19 patients. Convalescent plasma donors were screened as follows: 1) previously confirmed SARS-CoV-2 infection (by real-time PCR (RT-PCR)); 2) a subsequent negative PCR test followed by a 2-week waiting period; 3) an additional negative PCR test prior to plasmapheresis; and 4) confirmation of the presence of SARS-CoV-2 specific antibodies. Convalescent plasma was stored fresh (2-6°C) for up to 5 days or frozen (-30°C) for long-term storage. Donor peripheral blood and final plasma product were assayed for binding antibodies targeting the SARS-CoV-2 S-protein receptor-binding domain (RBD) and their titers measured by an enzyme-linked immunosorbent assay (ELISA). We performed 72 plasmaphereses resulting in 248 final products. Convalescent plasma contained an RBD-specific antibody titer (IgG) ranging from 1:100 to 1:3200 (median 1:800). The titer was congruent to the titer of the blood (n = 34) before collection (1:100-1:6400, median 1:800). Levels of IL-8 and LBP of donors were slightly increased. Therapeutic products derived from a human origin must undergo rigorous testing to ensure uniform quality and patient safety. Whilst previous publications recommended RBD-specific binding antibody titers of ≥ 1:320, we selected a minimum titer of 1:800 in order to maximize antibody delivery. Production of highly standardized convalescent plasma was safe, feasible and was readily implemented in the treatment of severely ill COVID-19 patients.