The mixture of a predetermined amount of virus and serially diluted reference sera is added to 96-well plates coated with fetuin, a liver protein with sialic acid and galactose at the glycan terminal, and then incubated overnight at 37C

The mixture of a predetermined amount of virus and serially diluted reference sera is added to 96-well plates coated with fetuin, a liver protein with sialic acid and galactose at the glycan terminal, and then incubated overnight at 37C. vaccine development after vaccine strain selection, which allows viruses to continue evolving with potential for antigenic drift and, thus, antigenic mismatch between the vaccine strain and the emerging epidemic strain. SARS-CoV-2 characterization has faced similar challenges with the additional barrier of the need for facilities with high biosafety levels due to its infectious nature. In this study, we review the primary analytic methods used for antigenic characterization of influenza and SARS-CoV-2 and discuss the barriers of these methods and current developments for addressing these challenges. family and are classified into four genera including type A, B, C, and the emerging type D [7, 8] based on their antigenic differences in the nucleoprotein and matrix 1 protein. Influenza viruses contain segmented, negative-sense, single-stranded RNA genomes. Influenza A viruses (IAVs) and influenza B viruses (IBVs) contain 8 viral RNA (vRNA) gene segments, whereas influenza C viruses (ICVs) and influenza D viruses (IDVs) contain 7 vRNA gene segments. Segments 1 (PB2), 2 (PB1), 3 (PA), 4 (HA), 5 (NP), 6 (NA), 7 (MP), and 8 (NS) of IAVs and IBVs encode polymerase basic protein 2 (PB2), polymerase basic protein 1 (PB1), polymerase acidic protein (PA), hemagglutinin (HA), nucleoprotein (NP), neuraminidase (NA), matrix proteins (M1 and M2), and nonstructural proteins (NS1 and NS2), respectively, which will be described in the subsequent sections. In addition, several novel accessory proteins of IAVs were identified that modulate viral pathogenicity, such as PB1-F2 [9] and NU-7441 (KU-57788) PB1-N40 [10] encoded by the PB1 gene and PA-X [11], PA-N155, and PA-N182 [12] by the PA gene. Evolution and antigenic variations of influenza viruses The low-fidelity, error-prone RNA-dependent RNA polymerase (RdRp) of IAVs lacks the 3 to 5 5 exonuclease proofreading capability, leading to a rapid mutation rate that ranges from 0.4 10?3 to 2.0 10?6 mutations per nucleotide per year, depending on virus strain and gene [13C17]. Although the outcome of most random mutations is detrimental or lethal, non-deleterious mutations may be preserved and subsequently amplified in the population if they confer a fitness advantage [18]. High mutation frequencies and within-host selective pressures create quasi-species [19C22], defined as a proliferating population of non-identical but closely related viral genomes as seen with most RNA viruses, including influenza viruses [23, 24]. Some mutations can be positively selected in order for a virus to escape from host antibody neutralization or to replicate more efficiently, leading to virus variants becoming predominant in the population [25]. Population-level fitness has also been shown to be increased by cooperative interactions between variants within a quasi-species [26C30]. However, the overall mutation (at the nucleotide sequence level) and amino NU-7441 (KU-57788) acid substitution (at the protein sequence level; from nonsynonymous mutations) frequencies are a complex association of NU-7441 (KU-57788) factors that are genus-, strain-, and gene-specific and are even environmentally influenced (i.e., temperature or pH). These within- and between-host immune selection pressures result in variable evolutionary rates [13]. The phenomenon that amino acid substitutions accumulating on surface glycoproteins of influenza viruses gradually alter their antigenicity is referred to as antigenic drift, which allows NU-7441 (KU-57788) influenza viruses to evade immune pressures from their hosts Rabbit polyclonal to IQCA1 and is responsible for seasonal influenza epidemics that necessitate annual vaccine reformulations. Unlike NU-7441 (KU-57788) mutations, reassortment results in genome restructuring. Reassortment occurs when two strains from a shared genus infect the same host cell and produce a novel viral genotype, i.e., an assembly of segments from each parental strain. As is the case of random mutations, most reassortant events are deleterious, usually due to segment incompatibility [31]. When reassortment leads to the introduction of a novel HA and/or NA gene into a naive population (a population without existing immunity), it is commonly referred to as antigenic shift [32]. Antigenic shift, in combination with sustained human-to-human transmission, is a requirement for the emergence of an influenza pandemic strain. Reassortments have led to the emergence of the 1957, 1968, and 2009 IAV pandemics [33C36], contributed to the severe epidemics of 1947, 1951, and 2003, and facilitated the rise in antiviral drug resistance [37]. The influenza vaccine is the most viable option for counteracting and reducing the impact of influenza.