Physicochemical effect of the N501Y, E484K/Q, K417N/T, L452R and T478K mutations on the SARS-CoV-2 spike protein RBD and its influence on agent fitness and on attributes developed by emerging variants of concern.

The spike protein comprises one of the main structural components of SARS-CoV-2 because it is directly involved in the infection process and viral transmission, and also because of its immunogenic properties, as an inducer of the protective antibodies production and as a vaccine component. The occurrence of mutations in this region or in other the virus genome regions, comprises a natural phenomenon in its evolution. However, they also occur due to the selective immune pressure, to which the agent is continuously subjected, especially in the spike protein immunodominant regions, such as the RBD. Mutations in the spike protein can change the virus' fitness, increasing its affinity for target cells, its transmissibility and its virulence. In addition, these mutations can giving it the potential ability to evade the protective antibodies action obtained from convalescent sera or vaccine origin, as well as those used in therapy, which may favor the virus expansion and compromise the infection control. Five mutations N501Y, E484K/Q, K417N/T, L452R and T478K, located in the spike protein RBD, have had a greater impact because they are associated with new attributes developed by the virus, which characterize the emerging variants of concern (VOCs) of SARS-Cov-2 identified so far. The occurrence of these mutations induces complex physicochemical effects that can alter the spike protein's structure and its function, which in turn, lead to changes in the agents' fitness. This manuscript discusses the attributes of VOCs associated with the physicochemical effects caused by the aforementioned mutations.

Acute hepatitis B virus infection or acute exacerbation of chronic hepatitis B infection: the differential serological diagnosis.

Acute exacerbations of chronic hepatitis B are common, and may even be the first presentation of hepatitis B virus (HBV) infection. Sometimes, patients involved in these scenarios may have mistaken diagnosis of acute hepatitis B. The reason for the confusion is that the two forms of infection manifestation resemble remarkably in clinical, biochemical, and serological features, such as apparent rapid onset of severe disease, advanced grades of encephalopathy, high aminotransferases and prolonged international normalized ratios (INRs), as well as positivity for HBsAg and for IgM anti-HBc antibodies and DNA detection. Therefore, these two entities cannot be distinguished easily without historical information of HBV-associated chronic infection or recent HBV exposure, information that is often inaccurate. Considering the different prognoses, treatment strategies, and the epidemiological impact in the public health context, the correct diagnosis is extremely important. Despite the lack of effective and reliable tests to differentiate between acute infection and acute exacerbation of chronic HBV infection, the expression and kinetic evaluation of viral markers present in the circulation of individuals infected, the observation of physical-chemical properties of specific antibodies, and the combination of these findings represent some strategies in serology that could assist in differentiating between the two entities, or at least in the guidance for the correct diagnosis.

Molecular mechanisms underlying HBsAg negativity in occult HBV infection.

Although genomic detection is considered the gold standard test on HBV infection identification, the HBsAg investigation is still the most frequent clinical laboratory request to diagnose HBV infection in activity. However, the non-detection of HBsAg in the bloodstream of chronic or acutely infected individuals has been a phenomenon often observed in clinical practice, despite the high sensitivity and specificity of screening assays standardized commercially and adopted in routine. The expansion of knowledge about the hepatitis B virus biology (replication/life cycle, genetic variability/mutability/heterogeneity), their biochemical and immunological properties (antigenicity and immunogenicity), in turn, has allowed to elucidate some mechanisms that may explain the occurrence of this phenomenon. Therefore, the negativity for HBsAg during the acute or chronic infection course may become a fragile or at least questionable result. This manuscript discusses some mechanisms that could explain the negativity for HBsAg in a serological profile of individuals with HBV infection in activity, or factors that could compromise its detection in the bloodstream during HBV infection.

The underlying mechanisms for the "simultaneous HBsAg and anti-HBs serological profile".

The course of HBV infection is determined by the interplay between viral replication via HBV protein production and the host's immune response. Therefore, the diagnosis of infection in clinical practice is established by the serological detection of HBV protein products as well as antibodies produced by the host. Although the serological findings for assessing the clinical course of infection are already well established, the expression of viral proteins and the dynamics of antibody production may vary during the natural course of infection. This causes the HBV infection to be occasionally associated with the presence of unusual serologic profiles, which can lead to doubts in the interpretation of results and mistaken serological diagnosis. The simultaneous detection of HBsAg and anti-HBs in the blood stream comprises an atypical serological profile, somewhat incoherent, whose significance can be complicated to establish. Outlined in this article are some immunological and molecular mechanisms which could justify the existence of this profile in which there is a great laboratorial and clinical interest.

The underlying mechanisms for the 'anti-HBc alone' serological profile.

The serological pattern, "anti-HBc alone", characterized by the presence of antibodies against the core antigen of hepatitis B virus (anti-HBc) as the only marker of hepatitis B, is not rare in a diagnostic setting. Depending on the prevalence of HBV infection and the patient group investigated, 1-31% of positive anti-HBc results are isolated positive findings. Anti-HBc alone is frequently observed in intravenous drug addicts, HIV-infected individuals, patients who are coinfected with HBV and hepatitis C virus, and pregnant women. However, it is not clear how this profile should be interpreted. Several studies have shown that anti-HBc alone is not only compatible with acute and resolved HBV infection but also with chronic infection. The reasons for the lack of HBsAg and anti-HBs in anti-HBc-alone individuals are not clear, but several mechanisms and possibilities have been suggested that could explain this phenomenon, some of which are delineated in this article.