**11. Viral meningitis, encephalitis and hemorrhagic fever S2 cell line model**

Herpes simplex virus was studied in Drosophila S2 cells where transfection of two viral proteins PILRα and gB responsible for binding to mammalian cells were expressed found to be poorly glycosylated [114]. The RNAi pathway was indulged by host cells to inhibit the Dengue virus (Flavivirus family) infection, by knocking down Argonaute (Ago1/2) and Dicer (Dcr1/2) showed sustained viral infection, currently clinical trial is underway NCT00936429 [115, 116]. Japanese encephalitis virus envelope glycoprotein E transfected in Drosophila S2 cells resulted in stable protein expression, this glycoprotein exposure in mice led antibody production against it [117]. Infection of Sindbis virus in live flies led activation of Notch, Jak– STAT and ImD pathway to intervene viral invasion [54]. Notch pathway mediated assimilation of ankyrin, plap, syx13, unc-13, csp, rab1 and rab8 during Sindbis virus infection in S2 cells [115]. The human antibody MR191 specific against Marburg virus was fused with recombinant RAVV GP ectodomain produced in S2 cell line [118]. The Zika virus structural envelope (E) protein were efficiently produced and secreted from transfected Drosophila S2 cell line model [119]. Flies produces RNAi against west Nile virus infection as a result of innate immune response similarly it was seen in S2 cell line, S2 cell lines were used for WNV infection, currently vaccine development NCT01477580 and NCT00707642 is underway [116, 120]. In a study mice were injected with glycoprotein GP of Ebola virus expressed in Drosophila S2 cell line found to produce antibodies against the infused antigen [121] (**Table 1**).


*Animal Models in Medicine and Biology*

was previously reported to be symbolized as comparable disease progression in *Drosophila melanogaster*. Ingestion of cholera bacterium results in lethal infection induced by the toxins in the intestinal cells of the flies. The toxins ingestion could not cause equivalent lethal effect on flies was explained previously. The *V. cholera* infection results in inhibition of adenylyl cyclase, Gsα, or the Gardos K+ channel causing death due to oral ingestion in flies. Clotrimazole a Potassium Calcium-Activated Channel Subfamily N Member 4 (KCNN4) inhibitor exposure increased flies susceptibility to *V. cholera* infection [61]. Quorum sensing is the ability to detect and to respond to a specific density of cell population through gene regulation [102]. *Drosophila melanogaster* initiates quorum sensing during vibrio cholera infection by suppressing succinate (substrate of KEBS cycle) uptake in flies intestine, limiting the wasting process [62]. Quorum sensing enables the bacterium to remain sessile in the flies gut and Vibrio polysaccharide (VPS) gene expression was

shown to have increased during *V. cholera* infection of flies [103].

**9. Importance of in-vitro model infection in Drosophila**

The Drosophila S2 cells were first discovered by I. Schneider in 1972 [104]. S2 cells are derived from primary cell culture of late phase embryo of *Drosophila melanogaster*. S2 cells are macrophage like cells potentially grows in serum free medium as non-adherent suspension. S2 cells can express variety of heterologous proteins, upto 12 proteins could be co-expressed at a time in highly controlled manner, doubling at a rate equivalent to any cell lines derived from human cancerous cell line [105]. These cells do not form coherent clusters with no noisy gene expression profiles by maintaining uniformity during expression and chromosomal aneuploidy gets compensated during expression self adjusted to one gene copy number per cell unlike cancerous lineage [106]. These viable and potent cellular characteristics of S2 cell allows to be chosen for vaccine development, large scale enzyme as well as hormones production similar to Chinese hamster ovary CHO cell lines [104, 107]. The post translational glycosylation process is often not achievable in S2 cells making it disadvantageous [105]. The viral infections models are slow in inducing fatality in immuno-suppressed mutant flies, 50% death occurs after around 18–30 days post infection in live model [44, 108]. Therefore, S2 cell line model could requite certain challenges usually observed during in-vivo infec-

**10. In-vitro model of epidemic and pandemic infectious disease**

Using drosophila S2 cell model a study showed that intercellular *Mycobacterium smegmatis* growth inside the host phagosomes is restricted by Rab7, CG8743, and the ESCRT factors [109]. *Cryptococcus neoformans* a fungi responsible for meningoencephalitis infection, S2 cells infected by this fungus up-regulates autophagy initiating proteins like Atg2a, Atg5 and Atg9a beside lysosomal markers like LAMP-1 and cathepsin D [110]. The hepatitis B virus surface antigen (HBsAg) coded by S gene was transfected in S2 cell line gave rise to no variation in expressed protein suggesting S2 cells useful for expression system [111]. The *Plasmodium falciparum* reticulocyte-binding protein homolog 5 (PfRH5) was expressed in S2 cells of Drosophila to produce non-glycosylated variants capable of binding to its receptor in rabbits resulted in IgG production against PfRH5 protein [112]. Highly potential vaccine VAR2CSA against malaria was successfully produced in S2 cells of

**116**

*Drosophila melanogaster* [113].

tion models.


**Table 1.**

*List of Drugs/vaccines screened or developed against Infectious diseases in* Drosophila melanogaster *as a model organism.*
