1.5.1 known to grow faster in adherent cultures as

1.5.1 Baby Hamster Kidney-21 cells
Cells used in conventional PRNT include Vero, LLC-MK2 and BHK-21 (Baby Hamster Kidney-21) cells 7. BHK-21 cells are used in this study as they are susceptible to multiple viruses, including human Adenovirus D, Reovirus 3, and Flaviviruses. They are also genetically stable and are known to grow faster in adherent cultures as required in PRNT 19.
BHK-21 cells (BHK strain 21) are fibroblast cell lines that originate from the kidneys of five unsexed, 1 day old hamsters on March 1961 by I.A. Macpherson and M.G.P. Stoker. These cells were produced from the species of Mesocricetus auratus (Syrian golden hamsters) 19.
However, cells frequently used in conventional PRNT (Vero, LLC-MK2, BHK-21) are only limited to measuring the neutralising activities of viral infectivity in the absence of Fc? receptor (Fc?R) 20.
1.5.2 Fc?R-expressing BHK cells
Fc?R-expressing BHK cells are also used in this study as it is highly similar to a person’s immune cells, particularly monocytes which comprises of macrophages and dendritic cells. These mammalian-derived cell lines also express the Fc? receptor.
As described in Section 1.2, neutralising antibodies produced by the humoral immunity forms a virus-antibody complex that can be phagocytosed by cells expressing Fc? receptors (monocytes) as they are capable of recognising a secondary infection by DENV. However, DENV has the ability to replicate upon phagocytosis by these cells as the heterologous virus is not neutralised by the antibodies. Therefore, Fc?R-expressing BHK cells mimic the mechanism of how mononuclear cells respond to a dengue infection through its expression of the Fcy receptor which enhances viral replication 21.
It is suggested that neutralising antibody titres of anti-DENV antibodies caused by vaccines or natural infection may vary the presence of enhancing activity is assayed using BHK-21 cells due to its lack of Fc? receptors. The neutralising antibody titres determined using Fc?R-expressing BHK-21 cells may better reflect protective immunity as DENV targets Fc?R-expressing cells, such as macrophages 22.
Thus, the secondary aim of this study is to compare the neutralising antibody titres of both BHK-21 and Fc?R-expressing BHK cells (conventional and alternative PRNT assay) to find out if PRNT50 would be affected by the presence of Fc? receptors. PRNT50 is the lowest concentration of antibodies where it is the reduction in the number of plaques by 50% by serum samples compared to the serum free virus.