No abstract

SARS-CoV-2 Omicron subvariants BA.2.12.1 and BA.4/5 have surged notably to become dominant in the United States and South Africa, respectively1,2. These new subvariants carrying further mutations in their spike proteins raise concerns that they may further evade neutralizing antibodies, thereby further compromising the efficacy of COVID-19 vaccines and therapeutic monoclonals. We now report findings from a systematic antigenic analysis of these surging Omicron subvariants. BA.2.12.1 is only modestly (1.8-fold) more resistant to sera from vaccinated and boosted individuals than BA.2. However, BA.4/5 is substantially (4.2-fold) more resistant and thus more likely to lead to vaccine breakthrough infections. Mutation at spike residue L452 found in both BA.2.12.1 and BA.4/5 facilitates escape from some antibodies directed to the so-called class 2 and 3 regions of the receptor-binding domain3. The F486V mutation found in BA.4/5 facilitates escape from certain class 1 and 2 antibodies but compromises the spike affinity for the viral receptor. The R493Q reversion mutation, however, restores receptor affinity and consequently the fitness of BA.4/5. Among therapeutic antibodies authorized for clinical use, only bebtelovimab retains full potency against both BA.2.12.1 and BA.4/5. The Omicron lineage of SARS-CoV-2 continues to evolve, successively yielding subvariants that are not only more transmissible but also more evasive to antibodies.

Na؉ binding near the primary specificity pocket of thrombin promotes the procoagulant, prothrombotic, and signaling functions of the enzyme. The effect is mediated allosterically by a communication between the Na ؉ site and regions involved in substrate recognition. Using a panel of 78 Ala mutants of thrombin, we have mapped the allosteric core of residues that are energetically linked to Na ؉ binding. These residues are Asp-189, Glu-217, Asp-222, and Tyr-225, all in close proximity to the bound Na ؉ . Among these residues, Asp-189 shares with Asp-221 the important function of transducing Na

The shedding of severe acute respiratory syndrome coronavirus (SARS-CoV) into saliva droplets plays a critical role in viral transmission. The source of high viral loads in saliva, however, remains elusive. Here we investigate the early target cells of infection in the entire array of respiratory tissues in Chinese macaques after intranasal inoculations with a single-cycle pseudotyped virus and a pathogenic SARS-CoV. We found that angiotensin-converting enzyme 2-positive (ACE2 ؉ ) cells were widely distributed in the upper respiratory tract, and ACE2؉ epithelial cells lining salivary gland ducts were the early target cells productively infected. Our findings also have implications for SARS-CoV early diagnosis and prevention.Severe acute respiratory syndrome (SARS) is a recently emerged human infectious disease caused by a zoonotic coronavirus (SARS-CoV) that has a mortality rate of approximately 10% (11,20,24,30). Although it is known that SARSCoV is transmitted via saliva droplets, the source of high viral loads (up to 6.38 ϫ 10 8 copies/ml) in patients' saliva remains elusive, especially during the acute phase of viral replication (41). We hypothesized that viral replication in the upper respiratory tract may contribute to the rapid viral shedding into saliva droplets. To address this hypothesis, it is necessary to investigate SARS-CoV infection at the site of viral entry, including the identification of early target cells.Our current understandings of the target cells for SARSCoV are largely based on autopsy specimens of patients who died of SARS. Multiple cell types in the lower respiratory tract were found to be infected, including type I alveolar epithelium, macrophages, and putative CD34 ϩ Oct-4 ϩ stem/progenitor cells in human lungs (2,7,10,13,28,29). These results, while very informative, do not address the question of which cell types support the initial seeding of infection in the upper respiratory tract. Since the SARS outbreak in humans has subsided and because many of the current scientific questions are difficult to address in humans, several animal models have been developed.Animal models that have been used to study SARS-CoV infection include mice, hamsters, ferrets, cats, and nonhuman primates (cynomolgus macaques, rhesus macaques, common marmosets, and African green monkeys) (1,12,14,22,26,27,32,33,35). Although none of these animal models reproduce lethal SARS, most support SARS-CoV infection to some extent and therefore have contributed greatly to attempts to develop vaccines and therapeutics (1,9,14,19,43). We have recently demonstrated that rhesus angiotensin-converting enzyme 2 (ACE2), the primary receptor of SARS-CoV, supports viral entry as efficiently as does its human homologue (3, 23). Moreover, Chinese-origin rhesus macaques (Macaca mulatta) experimentally infected with a pathogenic SARS-CoV developed lung damage similar to that seen in humans with SARS (31). The Chinese rhesus macaque model, therefore, offers us an opportunity to study the early target cells of SARS-CoV in the resp...

Hepatitis C virus (HCV) is an enveloped, positive-stranded RNA virus classified in the family Flaviviridae. Infection is often associated with chronic disease, sometimes resulting in hepatitis, cirrhosis, and hepatocellular carcinoma. Although chronic infection occurs in up to 70% of individuals, the mechanisms leading to viral persistence have not been defined. The principal site of replication is thought to be the liver, although several laboratories have suggested that HCV may infect a wider range of cell types, including monocytes/macrophages and B cells (28,33,44).HCV encodes two putative envelope glycoproteins, E1 and E2, which are believed to be type I integral transmembrane proteins with C-terminal hydrophobic anchor domains. In vitro expression studies have shown that both glycoproteins associate to form heterodimers, which accumulate in the endoplasmic reticulum, the proposed site for HCV assembly and budding (reviewed in reference 53). Being an enveloped virus, HCV likely interacts with specific cell surface receptors that either induce conformational changes in the E1 and E2 glycoproteins, resulting in fusion between the viral and cellular membranes, or mediate internalization of virus particles to endosomes, where the acidic environment triggers membrane fusion-inducing conformational changes. The E2 glycoprotein is thought to be responsible for initiating virus attachment (29,54,67,71), and we have hypothesized that the E1 glycoprotein contains the fusion peptide responsible for mediating fusion of the virus and cell membranes (31).The lack of in vitro systems for HCV propagation has hampered biological and physiochemical studies of the virion and its mechanism of cell entry, so that the cellular receptors remain unknown. Difficulties encountered in purifying sufficient quantities of HCV from plasma have limited studies with native virus. In addition, HCV purified from plasma has been reported to exist in association with immune complexes and plasma lipoproteins (2, 6, 57). The association of the virus with lipoproteins has led to the suggestion that HCV may use the low-density lipoprotein receptor to gain entry into cells (3,71).In the absence of native HCV particles, virus-like particles expressed in insect cell systems (11,15,63,67) and truncated versions of the E2 glycoprotein have been used as mimics to study virus-cell interactions (29,54,58). Truncated E2 binds specifically to human cells and was used to identify CD81 as a putative receptor for some HCV strains (54). Recent reports suggest antigenic differences between the truncated form of E2 and that present on virus-like particles for reactivity with E2-specific monoclonal antibodies and CD81 (15,63,67). Since CD81 is expressed on the majority of cell types, it is unlikely to be the sole determinant of viral tropism, and additional cell surface molecules may be required for HCV entry into a target cell (45).While virus receptors typically play important roles in defining virus tropism, other cell surface molecules can significantly enhanc...