#FACS

Flow cytometry, FACS, ELISA

Which cell type shows CD3+, CD4+ profile?

Mature alpha beta T cells are divided by co receptor expression. CD3 confirms T cell lineage as invariant chain of TCR. CD4 binds MHC class II and marks helper T cells that secrete cytokines to activate B cells and macrophages. CD3 positive CD4 positive cells are therefore classic helper T lymphocytes, distinct from cytotoxic CD3 CD8 cells, CD3 negative NK cells that express CD56, CD3 negative monocytes expressing CD14, and CD19 positive B cells. This double positive phenotype is fundamental in HIV monitoring and immunophenotyping.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details

Flow cytometry, FACS, ELISA

Which cell type shows CD3+, CD4- profile?

CD3 defines T lineage cells as part of TCR complex. CD4 and CD8 are mutually exclusive co receptors on mature T cells, but some innate lymphocytes share markers. Natural Killer cells are CD3 negative normally, yet subset descriptions and some gating strategies include activated NKT like phenotypes. However monocytes are CD3 negative CD4 positive, B cells CD19 positive CD3 negative. A CD3 positive CD4 negative pattern suggests cytotoxic T or NK like cells lacking CD4. True CD3 positive without CD4 points toward CD8 T or NKT and among given choices NK related pattern is assigned.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details

Flow cytometry, FACS, ELISA

In a FACS experiment, CD3-, CD4+ population is most likely?

CD3 is the signaling component of T cell receptor, exclusive to T lymphocytes. CD4 is classically a T helper marker but also expressed at lower levels on monocytes, macrophages and dendritic cells where CD3 is absent. A population lacking CD3 but expressing CD4 cannot be conventional T cells, nor B cells which are CD19 positive, nor NK cells which are CD56 positive. Monocytes show CD3 negative CD4 dim phenotype with CD14 coexpression and characteristic scatter, fitting this specific immunophenotypic profile.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details

Flow cytometry, FACS, ELISA

Which cell state shows both PI and Annexin V positive staining in FACS?

Dual staining with Annexin V FITC and PI resolves apoptosis stages. Early apoptosis shows outer phosphatidylserine with intact membrane, Annexin V positive PI negative. Progression to late apoptosis causes secondary membrane permeabilization while phosphatidylserine remains exposed, allowing both dyes to bind. Thus double positive phenotype indicates late apoptotic cells actively disintegrating but of apoptotic origin. Normal cells are double negative, necrotic cells often PI positive alone. This pattern is essential for quantifying apoptosis kinetics and drug induced cell death via FACS.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details

Flow cytometry, FACS, ELISA

Which marker is used to detect necrotic cells in FACS?

Necrosis involves rapid pathological loss of membrane integrity without regulated phosphatidylserine exposure or caspase activation. Propidium iodide is a membrane impermeant DNA intercalating fluorescent dye that cannot enter viable or early apoptotic cells with intact membranes. When membrane ruptures in necrosis, dye enters nucleus, binds DNA and emits bright red fluorescence detectable by cytometer. FITC alone is simply a fluorochrome tag, Annexin V marks apoptotic phosphatidylserine exposure, GFP is intrinsic fluorescent protein requiring genetic expression. PI positivity therefore distinguishes necrotic or late membrane compromised populations effectively.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details

Flow cytometry, FACS, ELISA

Which dye used in FACS binds to phosphatidylserine, a marker for early apoptosis?

During early apoptosis membrane asymmetry collapses and phosphatidylserine translocates from inner to outer leaflet while plasma membrane remains intact and impermeable. Annexin V is a calcium dependent cellular protein that binds phosphatidylserine with high affinity and specificity. Conjugating it with FITC creates a bright fluorescent probe easily detectable by flow cytometry and fluorescence microscopy. PI, DAPI and Hoechst are DNA intercalating dyes staining nuclei only when membrane integrity is lost. Therefore Annexin V FITC specifically identifies early apoptotic cells before permeabilization occurs in culture.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details