Human Coronavirus OC43
Human coronavirus OC43, also known as HCoV-OC43, is one type of coronavirus (CoV) with lower ability of infection. The respiratory symptom caused by HCoV-OC43 infection is usually similar to the common cold. It is first isolated by McIntosh et al. in 1967 from patients with upper respiratory tract infection by human embryonic trachea tissue culture (OC) Virus (IBV). According to the characteristics of the genome, CoV is divided into four genera (α, β, γ and δ). At present, CoV infecting human is divided into α (CHCoV-229E, NL63) and β (HCoV-OC43, HKUI, SARS-CoV and MERS-CoV).
What is The Structure of HCoV-OC43?
The total length of the genome of HCoV-OC43 is about 30.7kb, and the content of base pair GC is 36.9%. The 5' end has a hat structure, followed by a 65-98 bp leading sequence and an untranslated region (UTR) which is very important for replication and transcription. There is also a non-translation region at the 3'end, followed by poly (a) tail. The first 2/3 region of the genome encodes an ORF1ab containing 16 non-structural proteins (NSP), and the last 1/3 region encodes orf2a, HE, S, orfs5a, E, M and N (Figure 1). Orf1ab encodes nsp1-nsp6.
Figure 1. The structure of HCoV-OC43
*This diagram is derived from the publication on Nature Reviews
How does HCoV-OC43 Enter The Susceptible Cells?
Owczarek et al. found that the entry of HCoV-OC43 into human cells is largely achieved through the caveolin-1-dependent pathway of endocytosis, and the scission of virus-containing vesicles from the cell surface is dynamin-dependent  by confocal microscopy and molecular biology tools. Furthermore, the vesicle internalization process requires actin cytoskeleton rearrangements.
Notably, while host factors like interferon-inducible transmembrane proteins (IFITMs) often prevent the entry of coronaviruses like HCoV-229E, -NL63, SARS-CoV and MERS-CoV from entering cells through its various antiviral functions, IFITM2 and IFITM3 promote the entry and subsequent infection of HCoV-OC43 into human cells.
 Owczarek, Katarzyna, Szczepanski et al. Early events during human coronavirus OC43 entry to the cell [J]. Scientific Reports. 2018, 8(1), 7124.
 Dijkman R, Jebbink MF, Gaunt E, et al. The dominance of human coronavirus OC43 and NL63 infections in infants [J]. J Clin Virol. 2012, 53:135–9.