33 public questions tagged with this topic.
Infectious mononucleosis, also known as the "kissing disease, " is caused by the Epstein-Barr virus (EBV). This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Zoology section), Chapter: Human Health and Disease, Topic: Immunity, diseases and health maintenance.
Plateau phase, also termed stationary phase, occurs when culture reaches carrying capacity constrained by surface area for adherent cells or nutrient limits for suspension cells. Cell number stabilizes as division rate equals death rate, curve flattening. Molecular mechanisms include contact inhibition mediated by Hippo pathway: high cell density activates LATS1/2 kinases phosphorylating YAP leading to cytoplasmic retention and degradation preventing transcription of cyclin D1 and survivin. Cadherin engagement also induces p27Kip1. Simultaneously growth factor exhaustion, accumulation of inhibitory metabolites lactate and ammonia lowering pH from 7.4 toward 6.8, and oxygen gradients limit proliferation. Cells remain metabolically active, can differentiate, for example myoblasts fuse into myotubes when growth factors withdrawn. Proliferation markers Ki-67 decline while quiescence markers increase. Viability remains high if medium replenished. Recognizing plateau timing guides differentiation protocols and indicates need for passaging if continued exponential growth desired, preventing accidental entry into death phase where toxicity rises. Optimizing extracellular matrix coatings such as collagen improves attachment reducing lag duration significantly. This knowledge strengthens laboratory safety, protocol reproducibility, and regulatory compliance critical for translational research and clinical applications, ensuring reliable data and workforce protection.
Ref: Alberts MBoC Ch.17 Plateau contact inhibition Hippo YAP; Freshney Ch.13 Growth curve plateau stationary quiescence balance.
MDCK cells are premier model for epithelial physiology because they form highly polarized monolayers with distinct apical membrane enriched in glycoproteins with GPI anchors and basolateral membrane containing receptors for growth factors, enabling study of protein sorting signals such as tyrosine motifs and raft-dependent trafficking via Par3-Par6-aPKC polarity complex. They develop tight junctions that restrict paracellular diffusion, allowing measurement of drug permeability, P-glycoprotein mediated efflux, and toxicant effects on barrier integrity. In influenza research, MDCK is gold standard because expression of sialyltransferases creates receptors for influenza hemagglutinin: alpha2,3 sialic acids recognized by avian strains and alpha2,6 by human strains, allowing viral attachment, endocytosis, and productive replication with observable cytopathic effect. Hemagglutination assays, plaque titration, and testing of neuraminidase inhibitors oseltamivir and zanamivir rely on MDCK. This dual utility for membrane transport and influenza distinguishes MDCK from fibroblast lines used only for signaling or muscle lines for contractile studies. Co-culture with immune cells models viral transmission across epithelial barriers relevant to pandemic preparedness. This knowledge strengthens laboratory safety, protocol reproducibility, and regulatory compliance critical for translational research and clinical applications, ensuring reliable data and workforce protection.
Ref: Simons K & Fuller SD Annu Rev Cell Biol 1985 MDCK polarity; WHO Manual Influenza diagnostics: MDCK culture influenza virus study.
Vero cells are particularly valuable for vaccine production and virology because deletion of interferon alpha/beta genes prevents establishment of antiviral state normally triggered by viral RNA sensing via RIG-I and MDA5 activating IRF3. Consequently viruses replicate to high titers enabling efficient bulk production under Good Manufacturing Practice. Poliovirus inactivated polio vaccine, rabies vaccine, Japanese encephalitis vaccine, and rotavirus vaccine are produced in Vero microcarrier cultures. Regulatory agencies accept Vero because extensive documentation demonstrates absence of tumorigenicity at low passages and effective removal of host cell DNA during downstream purification using benzonase and chromatography. Compared to human diploid strains MRC-5 with limited lifespan of 42 doublings, Vero provides indefinite expansion lowering costs. In diagnostic virology, Vero supports plaque assays for virus titration due to clear cytopathic effect. Limitations include non-human glycosylation patterns differing in sialic acid linkages, making them less ideal for studies requiring authentic human post-translational modifications, where HEK293 or HepG2 lines are preferred for metabolism and protein folding investigations.
Ref: WHO Requirements for Vero cells for vaccine production TRS 978 Annex 3; Barrett et al Biologicals 2009 Vero interferon deficiency vaccine.
Vero cell line originates from kidney epithelial tissue excised from adult African green monkey Chlorocebus aethiops, formerly Cercopithecus aethiops, at Chiba University Japan in 1962 by Yasumura and Kawakita. Designation Vero derived from Esperanto phrase Verda Reno meaning green kidney. Cells exhibit epithelial-like cobblestone morphology, anchorage dependence, contact inhibition, and were initially diploid but later became aneuploid after continuous passage. Critical molecular feature is homozygous deletion of approximately 9 megabase region on chromosome 12 encoding type I interferon gene cluster including IFNA and IFNB, disabling interferonbeta production and interferonstimulated gene response to viral infection. This interferon deficiency renders Vero highly permissive to wide range of viruses including poliovirus, measles, rabies, and SARS coronavirus while lacking adventitious retroviruses. Sublineages such as Vero E6 express high levels of ACE2 receptor facilitating SARS-CoV-2 isolation, and Vero 76 useful for hemorrhagic fever viruses. WHO endorsed Vero for vaccine manufacture due to safety profile. Authentication of Vero sublineages via genome sequencing prevents misidentification affecting vaccine lot consistency. This knowledge strengthens laboratory safety, protocol reproducibility, and regulatory compliance critical for translational research and clinical applications, ensuring reliable data and workforce protection.
Ref: Yasumura Y & Kawakita Y Nippon Rinsho 1963 Vero African green monkey kidney; Desmyter et al J Virol 1968 Interferon deficiency in Vero.
AIDS is caused by the Human Immunodeficiency Virus (HIV), which attacks the immune system.
Ref: NCERT Class 12 Biology Chapter 7: Human Health and Disease Immune Disorders - Allergies Autoimmunity and AIDS
The common cold is caused by rhinoviruses, which infect the upper respiratory tract.
Ref: NCERT Class 12 Biology Chapter 7: Human Health and Disease Common Diseases - Viral - Common Cold and Other Viral Diseases
T-cytotoxic cells (CD8+ cells) destroy virus-infected cells by inducing apoptosis.
Ref: NCERT Class 12 Biology Chapter 7: Human Health and Disease Common Diseases - Viral - Common Cold and Other Viral Diseases
M. W. Beijerinck showed that extract from infected tobacco plants could infect healthy plants. He called the infectious fluid âContagium vivum fluidum,â meaning infectious living fluid.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Five Kingdom Classification and Kingdom Plantae Animalia
Viroids are infectious agents made of low-molecular-weight RNA. They lack the protein coat found in viruses and were discovered by T. O. Diener.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Viruses Viroids Prions and Lichens
The particle is a virus. Viruses remain inert outside their specific host cells but take over the host-cell machinery after infection to produce additional virus particles.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Viruses Viroids Prions and Lichens
The agent is a viroid. T. O. Diener discovered viroids while studying potato spindle tuber disease. Viroids consist of free RNA of low molecular weight and lack the protein coat found in viruses.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Viruses Viroids Prions and Lichens
