Ly6c+ “inflammatory monocytes” are microglial precursors recruited in a pathogenic manner in West Nile virus encephalitis

In a lethal West Nile virus (WNV) model, central nervous system infection triggered a threefold increase in CD45int/CD11b+/CD11c− microglia at days 6–7 postinfection (p.i.). Few microglia were proliferating, suggesting that the increased numbers were derived from a migratory precursor cell. Depletion of “circulating” (Gr1−(Ly6Clo)CX3CR1+) and “inflammatory” (Gr1hi/Ly6Chi/CCR2+) classical monocytes during infection abrogated the increase in microglia. C57BL/6 chimeras reconstituted with cFMS–enhanced green fluorescent protein (EGFP) bone marrow (BM) showed large numbers of peripherally derived (GFP+) microglia expressing GR1+(Ly6C+) at day 7 p.i., suggesting that the inflammatory monocyte is a microglial precursor. This was confirmed by adoptive transfer of labeled BM (Ly6Chi/CD115+) or circulating inflammatory monocytes that trafficked to the WNV-infected brain and expressed a microglial phenotype. CCL2 is a chemokine that is highly expressed during WNV infection and important in inflammatory monocyte trafficking. Neutralization of CCL2 not only reduced the number of GFP+ microglia in the brain during WNV infection but prolonged the life of infected animals. Therefore, CCL2-dependent inflammatory monocyte migration is critical for increases in microglia during WNV infection and may also play a pathogenic role during WNV encephalitis

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Open Access

Targeted blockade in lethal West Nile virus encephalitis indicates a crucial role for very late antigen (VLA)-4-dependent recruitment of nitric oxide-producing macrophage

Systemic Low-Dose UVB Inhibits CD8 T Cells and Skin Inflammation by Alternative and Novel Mechanisms

Exposure to UVB radiation before antigen delivery at an unirradiated site inhibits functional immunological responses. Mice treated dorsally with suberythemal low-dose UVB and immunized with ova in abdominal skin generated ova-specific CD8 T cells with a significantly decreased activation, expansion, and cytotoxic activity compared with unirradiated mice. UVB also impaired the delayed-type hypersensitivity (DTH) reaction to ova. Transfer of CD4+CD25+ cells from UVB-exposed mice did not suppress the ova-specific CD8 T-cell response or DTH reaction in unexposed mice, confirming that systemic low-dose UVB does not induce long-lived functional regulatory CD4+CD25+ T cells. Repairing cyclobutane pyrimidine dimer–type DNA damage and blocking aryl hydrocarbon receptor signaling also did not reverse the immunosuppressive effect of UVB on ova-specific CD8 T cells and DTH, suggesting that cyclobutane pyrimidine dimers and the aryl hydrocarbon receptor are not required in systemic low-dose UVB-induced immunosuppression. The known UVB chromophore, cis-urocanic acid, and reactive oxygen species triggered the inhibition of DTH caused by UVB, but they were not involved in the modulation of CD8 T cells. These findings indicate that systemic low-dose UVB impedes the primary response of antigen-specific CD8 T cells by a novel mechanism that is independent of pathways known to be involved in systemic suppression of DTH

Targeted blockade in lethal West Nile virus encephalitis indicates a crucial role for very late antigen (VLA)-4-dependent recruitment of nitric oxide-producing macrophages

<p>Abstract</p> <p>Infiltration of Ly6C^hi monocytes from the blood is a hallmark of viral encephalitis. In mice with lethal encephalitis caused by West Nile virus (WNV), an emerging neurotropic flavivirus, inhibition of Ly6C^hi monocyte trafficking into the brain by anti-very late antigen (VLA)-4 integrin antibody blockade at the time of first weight loss and leukocyte influx resulted in long-term survival of up to 60% of infected mice, with subsequent sterilizing immunity. This treatment had no effect on viral titers but appeared to be due to inhibition of Ly6C^hi macrophage immigration. Although macrophages isolated from the infected brain induced WNV-specific CD4⁺ T-cell proliferation, T cells did not directly contribute to pathology, but are likely to be important in viral control, as antibody-mediated T-cell depletion could not reproduce the therapeutic benefit of anti-VLA-4. Instead, 70% of infiltrating inflammatory monocyte-derived macrophages were found to be making nitric oxide (NO). Furthermore, aminoguanidine-mediated inhibition of induced NO synthase activity in infiltrating macrophages significantly prolonged survival, indicating involvement of NO in the immunopathology. These data show for the first time the therapeutic effects of temporally targeting pathogenic NO-producing macrophages during neurotropic viral encephalitis.</p

Ultraviolet B Suppresses Immunity by Inhibiting Effector and Memory T Cells

Contact hypersensitivity is a T-cell-mediated response to a hapten. Exposing C57BL/6 mice to UV B radiation systemically suppresses both primary and secondary contact hypersensitivity responses. The effects of UVB on in vivo T-cell responses during UVB-induced immunosuppression are unknown. We show here that UVB exposure, before contact sensitization, inhibits the expansion of effector CD4+ and CD8+ T cells in skin-draining lymph nodes and reduces the number of CD4+ and IFN-γ+ CD8+ T cells infiltrating challenged ear skin. In the absence of UVB, at 10 weeks after initial hapten exposure, the ear skin of sensitized mice was infiltrated by dermal effector memory CD8+ T cells at the site of challenge. However, if mice were previously exposed to UVB, this cell population was absent, suggesting an impaired development of peripheral memory T cells. This finding occurred in the absence of UVB-induced regulatory CD4+ T cells and did not involve prostaglandin E2, suggesting that the importance of these two factors in mediating or initiating UVB-induced immunosuppression is dependent on UVB dose. Together these data indicate that in vivo T-cell responses are prone to immunoregulation by UVB, including a novel effect on both the activated T-cell pool size and the development of memory T cells in peripheral compartments