BCG immunization induces CX3CR1hi effector memory T cells to provide cross-protection via IFN-γ-mediated trained immunity.

After a century of using the Bacillus Calmette-Guérin (BCG) vaccine, our understanding of its ability to provide protection against homologous (Mycobacterium tuberculosis) or heterologous (for example, influenza virus) infections remains limited. Here we show that systemic (intravenous) BCG vaccination provides significant protection against subsequent influenza A virus infection in mice. We further demonstrate that the BCG-mediated cross-protection against influenza A virus is largely due to the enrichment of conventional CD4+ effector CX3CR1hi memory αß T cells in the circulation and lung parenchyma. Importantly, pulmonary CX3CR1hi T cells limit early viral infection in an antigen-independent manner via potent interferon-γ production, which subsequently enhances long-term antimicrobial activity of alveolar macrophages. These results offer insight into the unknown mechanism by which BCG has persistently displayed broad protection against non-tuberculosis infections via cross-talk between adaptive and innate memory responses.

Neonatal imprinting of alveolar macrophages via neutrophil-derived 12-HETE.

Resident-tissue macrophages (RTMs) arise from embryonic precursors1,2, yet the developmental signals that shape their longevity remain largely unknown. Here we demonstrate in mice genetically deficient in 12-lipoxygenase and 15-lipoxygenase (Alox15-/- mice) that neonatal neutrophil-derived 12-HETE is required for self-renewal and maintenance of alveolar macrophages (AMs) during lung development. Although the seeding and differentiation of AM progenitors remained intact, the absence of 12-HETE led to a significant reduction in AMs in adult lungs and enhanced senescence owing to increased prostaglandin E2 production. A compromised AM compartment resulted in increased susceptibility to acute lung injury induced by lipopolysaccharide and to pulmonary infections with influenza A virus or SARS-CoV-2. Our results highlight the complexity of prenatal RTM programming and reveal their dependency on in trans eicosanoid production by neutrophils for lifelong self-renewal.

Virus-Induced Acute Respiratory Distress Syndrome Causes Cardiomyopathy Through Eliciting Inflammatory Responses in the Heart.

BACKGROUND: Viral infections can cause acute respiratory distress syndrome (ARDS), systemic inflammation, and secondary cardiovascular complications. Lung macrophage subsets change during ARDS, but the role of heart macrophages in cardiac injury during viral ARDS remains unknown. Here we investigate how immune signals typical for viral ARDS affect cardiac macrophage subsets, cardiovascular health, and systemic inflammation. METHODS: We assessed cardiac macrophage subsets using immunofluorescence histology of autopsy specimens from 21 patients with COVID-19 with SARS-CoV-2-associated ARDS and 33 patients who died from other causes. In mice, we compared cardiac immune cell dynamics after SARS-CoV-2 infection with ARDS induced by intratracheal instillation of Toll-like receptor ligands and an ACE2 (angiotensin-converting enzyme 2) inhibitor. RESULTS: In humans, SARS-CoV-2 increased total cardiac macrophage counts and led to a higher proportion of CCR2+ (C-C chemokine receptor type 2 positive) macrophages. In mice, SARS-CoV-2 and virus-free lung injury triggered profound remodeling of cardiac resident macrophages, recapitulating the clinical expansion of CCR2+ macrophages. Treating mice exposed to virus-like ARDS with a tumor necrosis factor α-neutralizing antibody reduced cardiac monocytes and inflammatory MHCIIlo CCR2+ macrophages while also preserving cardiac function. Virus-like ARDS elevated mortality in mice with pre-existing heart failure. CONCLUSIONS: Our data suggest that viral ARDS promotes cardiac inflammation by expanding the CCR2+ macrophage subset, and the associated cardiac phenotypes in mice can be elicited by activating the host immune system even without viral presence in the heart.

Pregnancy enhances antiviral immunity independent of type I IFN but dependent on IL-17-producing γδ+ T cells in the nasal mucosa.

Pregnancy is associated with profound changes in immunity. However, pregnancy-related respiratory immune adaptations in response to influenza infection and their impact on disease severity remain unclear. Here, we describe, in a preclinical model of mid-gestation pregnancy, a mechanism of enhanced host defense against influenza A virus (IAV) localized to the nasal cavity that limits viral replication and reduces the magnitude of intrapulmonary immune responses. Consequently, the pregnant mice show reduced pulmonary pathology and preserved airway function after IAV infection. The early restriction of viral replication is independent of type I interferon (IFN) but dependent on increased antimicrobial peptides (AMPs) driven by interleukin-17+ (IL-17+) γδ+ T cells within the nasal passages. This pathway of host defense against IAV infection in the upper airways during pregnancy restricts early viral infection and prevents virus dissemination into the lung supporting maternal fitness.

The gift of preexisting immunity for developing an alternative vaccine strategy.

Despite the worldwide application of vaccination and other antiviral interventions, pulmonary viral infections remain a persistent threat to human health. The 1918 influenza pandemic killed more than 40 million people in just one year, and the SARS-CoV-2 pandemic has killed more than 6.9 million people since 2019. While the current approved COVID-19 vaccines are administered parenterally and induce systemic immunity, they only prevent the progression to severe disease. Thus, other vaccine platforms are still needed for completely preventing the disease and subsequent transmission. In this issue of the JCI, Kawai et al. present an adjuvant-free subunit (RBD-HA) fusion vaccine, which produces robust IgG and IgA antibody responses against SARS-CoV-2, enriched within the nasal cavity, by using the host's preexisting immunity to influenza infection. This preclinical study has tremendous implications for future mucosal vaccine design and provides a roadmap for generating a safer and effective intranasal vaccine against pulmonary infections.

Characterization of the Clinical Evidence Supporting Repository Corticotropin Injection for FDA-Approved Indications: A Scoping Review.

IMPORTANCE: Repository corticotropin injection is an expensive medication that was approved in 1952 for the treatment of many inflammatory conditions. The clinical evidence supporting the use of repository corticotropin (hereinafter referred to as corticotropin) has been weak, perhaps because its approval predated the modern review standards of the US Food and Drug Administration (FDA). OBJECTIVE: To characterize the clinical evidence supporting the use of corticotropin for its FDA-approved indications. EVIDENCE REVIEW: Studies were identified via electronic searches of Ovid MEDLINE, the Cumulative Index of Nursing and Allied Health Literature (CINAHL), and the Cochrane Central Register of Controlled Trials (CENTRAL) from database inception to May 12, 2021 (the MEDLINE search was updated on June 8, 2021). Bibliographies of retrieved articles were also reviewed through ClinicalTrials.gov, FDA documents, and the manufacturer's website. Search terms included HP Acthar, ACTH gel, repository corticotropin, and terms for specific diseases, such as multiple sclerosis, nephrotic syndrome, rheumatoid arthritis, and West syndrome (or spasms, infantile). The review included randomized clinical trials (RCTs), nonrandomized and single-arm clinical trials, and prospective cohort studies that compared corticotropin with an active comparator, placebo, or no treatment. Data were extracted by 1 reviewer and verified by a second. Disagreements were resolved through discussion. Studies were qualitatively synthesized by indication to summarize important design features and results. FINDINGS: Of 1059 records screened, 203 full-text articles were assessed for eligibility. A total of 41 studies involving 2235 participants met inclusion criteria; of those, 11 involved infantile spasms, 10 involved multiple sclerosis (MS), 11 involved rheumatological conditions, 7 involved nephrotic syndrome, 1 involved ocular conditions, and 1 involved sarcoidosis. Overall, 19 studies either included a single arm or exclusively compared different corticotropin dosing strategies. The evidence was most robust for the treatment of infantile spasms and MS. The largest number of studies comparing corticotropin with an active agent (n = 4) or placebo (n = 5) pertained to MS, with almost all studies finding that corticotropin performed better than placebo but no different than corticosteroids. For the treatment of infantile spasms, 8 controlled studies were identified (6 were randomized); of those, only 1 small RCT found corticotropin to be significantly superior to corticosteroids. Studies of patients with other conditions (n = 20) frequently lacked a control group (n = 12), were placebo-controlled (n = 5), or exclusively examined different corticotropin dosing strategies (n = 2). Placebo-controlled RCTs of rheumatoid arthritis, ankylosing spondylitis, optic neuritis, systemic lupus erythematosus, and nephrotic syndrome were generally small and did not consistently demonstrate that corticotropin was superior to placebo. Blinded RCTs showed a similar or greater number of adverse effects with corticotropin relative to corticosteroids. CONCLUSIONS AND RELEVANCE: In this scoping review, few RCTs supported the clinical benefit of corticotropin for most FDA-approved indications. Most RCTs found that corticotropin was not superior to corticosteroids for treating relapses of MS or infantile spasms.

Mitochondrial cyclophilin D promotes disease tolerance by licensing NK cell development and IL-22 production against influenza virus.

Severity of pulmonary viral infections, including influenza A virus (IAV), is linked to excessive immunopathology, which impairs lung function. Thus, the same immune responses that limit viral replication can concomitantly cause lung damage that must be countered by largely uncharacterized disease tolerance mechanisms. Here, we show that mitochondrial cyclophilin D (CypD) protects against IAV via disease tolerance. CypD-/- mice are significantly more susceptible to IAV infection despite comparable antiviral immunity. This susceptibility results from damage to the lung epithelial barrier caused by a reduction in interleukin-22 (IL-22)-producing natural killer (NK) cells. Transcriptomic and functional data reveal that CypD-/- NK cells are immature and have altered cellular metabolism and impaired IL-22 production, correlating with dysregulated bone marrow lymphopoiesis. Administration of recombinant IL-22 or transfer of wild-type (WT) NK cells abrogates pulmonary damage and protects CypD-/- mice after IAV infection. Collectively, these results demonstrate a key role for CypD in NK cell-mediated disease tolerance.

BCG vaccination provides protection against IAV but not SARS-CoV-2.

Since the vast majority of species solely rely on innate immunity for host defense, it stands to reason that a critical evolutionary trait like immunological memory evolved in this primitive branch of our immune system. There is ample evidence that vaccines such as bacillus Calmette-Guérin (BCG) induce protective innate immune memory responses (trained immunity) against heterologous pathogens. Here we show that while BCG vaccination significantly reduces morbidity and mortality against influenza A virus (IAV), it fails to provide protection against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). In contrast to IAV, SARS-CoV-2 infection leads to unique pulmonary vasculature damage facilitating viral dissemination to other organs, including the bone marrow (BM), a central site for BCG-mediated trained immunity. Finally, monocytes from BCG-vaccinated individuals mount an efficient cytokine response to IAV infection, while this response is minimal following SARS-CoV-2. Collectively, our data suggest that the protective capacity of BCG vaccination is contingent on viral pathogenesis and tissue tropism.

Cardiac failure following inadvertent administration of high-dose epinephrine subcutaneously.

Our aim is to report the consequences of epinephrine toxicity leading to cardiac failure in a child and the successful management with dopamine and milrinone. A previously healthy 13-year-old girl undergoing a left tympanomastoidectomy was inadvertently administered 10 mL of 1:1000 epinephrine subcutaneously (0.175 mg/kg) on the left post auricular region in lieu of lidocaine. She developed sudden supraventricular tachycardia, hypertension and flash pulmonary edema. She was initially treated with propofol, nitrogycerin and increased peak end-expiratory pressure. Within 4 h, she remained tachycardic, but was hypotensive with an increased central venous pressure. Electrocardiogram and echocardiogram investigations showed ST changes indicative of myocardial ischemia and globally reduced function, respectively. Dopamine infusion was administered, together with milrinone, resulting in a gradual improvement of cardiac function within 3 days. She was transitioned to enalapril and discharged home. This case highlights the clinical features of high dose epinephrine toxicity secondary to iatrogenic subcutaneous overdose followed by hypotension and pulmonary edema as a possible late effect of epinephrine and the successful management of secondary cardiac failure with administration of dopamine, milrinone and enalapril.