Cellular Immunology & Diagnostic Flow Cytometry

Vocabulary flashcards covering key terms from the lecture on cellular immunology, flow cytometry techniques, primary and acquired immunodeficiencies, and neutrophil functional testing.

Hematopoietic Stem Cell (HSC)

Multipotent precursor that gives rise to all blood cell lineages during normal haematopoiesis.

Flow Cytometry

Technique that passes single cells through a laser to count and characterise them by light scatter and fluorescence.

Forward Scatter (FSC)

Light scattered in the same direction as the laser beam; correlates with cell size.

Side Scatter (SSC)

Light scattered at 90° to the laser; reflects intracellular granularity/complexity.

Fluorochrome

Fluorescent dye attached to antibodies; absorbs laser light and emits at a longer wavelength for detection.

CD Marker

Cluster-of-Differentiation molecule on cell surfaces used to identify leukocyte subsets.

Lymphocyte Phenotyping

Flow-cytometric identification and enumeration of T, B and NK cell populations using CD markers.

TruCount Tube

Flow cytometry tube containing a known number of beads for absolute cell counting.

CD45

Pan-leukocyte marker expressed on haematopoietic cells including lymphocytes.

CD3

T-cell surface molecule; defines total T-cell population.

CD4

Marker for helper T cells; primary HIV target.

CD8

Marker for cytotoxic T cells.

CD19

Surface marker specific for B cells.

CD16/CD56

Markers that together identify natural killer (NK) cells.

FITC

Fluorochrome fluorescing green (emission ~520 nm) excited by 488 nm blue laser.

PE (Phycoerythrin)

Yellow-orange fluorochrome (emission ~578 nm) commonly used in multicolour panels.

APC (Allophycocyanin)

Red-emitting fluorochrome (emission ~660 nm) excited by 633 nm red laser.

Severe Combined Immunodeficiency (SCID)

Group of primary immunodeficiencies with absent T, B and often NK cells causing life-threatening infections.

X-linked SCID

SCID caused by mutations in the common γ-chain of several IL receptors; no T or NK cells, non-functional B cells.

ADA SCID

SCID due to adenosine deaminase deficiency; dATP accumulation blocks DNA synthesis in T and B cells.

PNP SCID

Purine nucleoside phosphorylase deficiency leading to toxic dGTP build-up and T-cell loss.

Omenn Syndrome

SCID variant from RAG-1/RAG-2 mutations impairing V(D)J recombination of T and B-cell receptors.

Bare Lymphocyte Syndrome

Defect in MHC-II gene regulation; antigen-presenting cells lack MHC-II expression.

DiGeorge Syndrome (22q11 Deletion)

Primary immunodeficiency with thymic aplasia, cardiac defects, cleft palate and hypocalcaemia.

Hyper IgM Syndrome

Defect in Ig class switching, usually due to missing CD40L or CD40; high IgM, low IgG/IgA/IgE.

CD40

Receptor on B cells needed for T-cell-induced class switching.

CD40 Ligand (CD40L)

Molecule on activated T cells that binds CD40 to trigger immunoglobulin class switching.

Common Variable Immune Disorder (CVID)

Heterogeneous condition with low immunoglobulins and/or B-cell abnormalities; treated with IgG replacement.

Human Immunodeficiency Virus (HIV)

Virus infecting CD4+ T cells, causing acquired immunodeficiency and opportunistic infections.

Rituximab

Anti-CD20 monoclonal antibody depleting B cells; can cause therapy-related cellular immunodeficiency.

Neutrophil

Polymorphonuclear granulocyte responsible for bacterial defense via phagocytosis and respiratory burst.

Respiratory Burst

Rapid production of reactive oxygen species in neutrophils mediated by NADPH oxidase after stimulation.

NADPH Oxidase

Multi-component enzyme complex generating superoxide during the neutrophil respiratory burst.

Phorbol Myristate Acetate (PMA)

Potent stimulant used in vitro to trigger neutrophil respiratory burst.

Dihydrorhodamine (DHR) Assay

Flow-cytometric test measuring burst activity by oxidation of non-fluorescent DHR to fluorescent rhodamine 123.

Nitro Blue Tetrazolium (NBT) Test

Alternative assay for respiratory burst; reduction of NBT dye forms blue formazan precipitate.

Chronic Granulomatous Disease (CGD)

Inherited disorder with defective NADPH oxidase leading to recurrent bacterial/fungal infections and granulomas.

Leukocyte Adhesion Deficiency (LAD)

Rare defect in cell adhesion molecules (e.g., CD18) preventing neutrophil migration to infection sites.

fMLP

Formyl-methionyl-leucyl-phenylalanine; bacterial peptide that chemotactically activates neutrophils.

Superoxide Dismutase

Enzyme converting superoxide anion to hydrogen peroxide during respiratory burst.

Gene Therapy

Therapeutic delivery of functional genes via viral vectors to correct inherited immunodeficiencies like SCID or CGD.

Stem Cell Transplant (SCT)

Infusion of donor haematopoietic stem cells to reconstitute immune function in severe immunodeficiencies.

Quality Control (QC) in Flow Cytometry

Procedures ensuring instrument performance and assay validity, critical before reporting abnormal results.

TruCount Beads

Fluorescent beads of known concentration used to calculate absolute cell counts in flow cytometry.

HLA-DR

MHC class II molecule; elevated on activated T cells and B cells, absent in bare lymphocyte syndrome.

Gamma/Delta T Cell

Minor T-cell subset expressing γδ TCR; detected when CD3 total exceeds CD4+CD8+ sum in phenotyping.