L-SIGN is a receptor on liver sinusoidal endothelial cells for SARS-CoV-2 virus.

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remains a pandemic. Severe disease is associated with dysfunction of multiple organs, but some infected cells do not express ACE2, the canonical entry receptor for SARS-CoV-2. Here, we report that the C-type lectin receptor L-SIGN interacted in a Ca2+-dependent manner with high-mannose-type N-glycans on the SARS-CoV-2 spike protein. We found that L-SIGN was highly expressed on human liver sinusoidal endothelial cells (LSECs) and lymph node lymphatic endothelial cells but not on blood endothelial cells. Using high-resolution confocal microscopy imaging, we detected SARS-CoV-2 viral proteins within the LSECs from liver autopsy samples from patients with COVID-19. We found that both pseudo-typed virus enveloped with SARS-CoV-2 spike protein and authentic SARS-CoV-2 virus infected L-SIGN-expressing cells relative to control cells. Moreover, blocking L-SIGN function reduced CoV-2-type infection. These results indicate that L-SIGN is a receptor for SARS-CoV-2 infection. LSECs are major sources of the clotting factors vWF and factor VIII (FVIII). LSECs from liver autopsy samples from patients with COVID-19 expressed substantially higher levels of vWF and FVIII than LSECs from uninfected liver samples. Our data demonstrate that L-SIGN is an endothelial cell receptor for SARS-CoV-2 that may contribute to COVID-19-associated coagulopathy.

Role of the skin biopsy in the diagnosis of atypical hemolytic uremic syndrome.

INTRODUCTION: Atypical hemolytic uremic syndrome (aHUS) is a prototypic thrombotic microangiopathy attributable to complement dysregulation. In the absence of complement inhibition, progressive clinical deterioration occurs. The authors postulated that a biopsy of normal skin could corroborate the diagnosis of aHUS through the demonstration of vascular deposits of C5b-9. MATERIALS AND METHODS: Biopsies of normal skin from 22 patients with and without aHUS were processed for routine light microscopy and immunofluorescent studies. An assessment was made for vascular C5b-9 deposition immunohistochemically and by immunofluorescence. The biopsies were obtained primarily from the forearm and/or deltoid. RESULTS: Patients with classic features of aHUS showed insidious microvascular changes including loose luminal platelet thrombi, except in 2 patients in whom a striking thrombogenic vasculopathy was apparent in biopsied digital ulcers. Extensive microvascular deposits of the membrane attack complex/C5b-9 were identified, excluding 1 patient in whom eculizumab was initiated before biopsy. In 5 of the 7 patients where follow-up was available, the patients exhibited an excellent treatment response to eculizumab. Patients without diagnostic clinical features of aHUS failed to show significant vascular deposits of complement, except 2 patients with thrombotic thrombocytopenic purpura including 1 in whom a Factor H mutation was identified. CONCLUSIONS: In a clinical setting where aHUS is an important diagnostic consideration, extensive microvascular deposition of C5b-9 supports the diagnosis of either aHUS or a subset of thrombotic thrombocytopenic purpura patients with concomitant complement dysregulation; significant vascular C5b-9 deposition predicts clinical responsiveness to eculizumab.

Hepatitis A and B immunizations of individuals infected with human immunodeficiency virus.

All persons at risk for infection with human immunodeficiency virus (HIV) types 1 and 2, including men who have sex with men, those with multiple heterosexual contacts, abusers of illegal injection drugs, and persons frequently exposed to blood and blood products, are also at high risk for hepatitis A virus (HAV) and acute and chronic hepatitis B virus (HBV) infections. HIV can prolong the duration and increase the level of HAV viremia and augment HAV-related liver abnormalities. HIV also magnifies HBV viremia and the risk of HBV reactivation, chronic active HBV infection, cirrhosis, and death. Because of these concerns, hepatitis A vaccination is recommended for all HIV-positive/HAV seronegative persons, with 2 standard doses given 6 to 12 months apart. Immune response to hepatitis A vaccines is excellent, even in moderately immune-suppressed individuals. Hepatitis B vaccination is also recommended for all HIV-positive persons lacking prior immunity. However, immune reactivity to hepatitis B vaccines is frequently suboptimal in terms of patients' rate of response, antibody titer, and durability. Relatively high CD4+ T-cell counts (> or =500/mm3) and low levels of HIV viremia (<1,000 RNA genome copies/mL plasma) are necessary to ensure adequate hepatitis B vaccine response. Higher hepatitis B vaccine doses, prolongation of the vaccination schedule, or both, as prescribed for many patients with non-HIV-related immune deficiencies, may be considered initially. Revaccination should be instituted if postvaccination titers of antibodies to hepatitis B surface antigen are <10 mIU/mL (<10 IU/L). Nonresponders may also react to a subsequent vaccine course if CD4+ T-cell counts rise to 500/mm3 following institution of highly active antiretroviral therapy; vaccine adjuvant trials are under way. Universal, age-based immunization of all young and middle-aged adults appears to be the most comprehensive way of protecting all populations who are at high risk.