HAT selection uses hypoxanthine, aminopterin and thymidine to distinguish cells able to maintain nucleotide supply through salvage metabolism under de novo synthesis blockade. In a conventional hybridoma scheme it selects suitable fusion products, not antigen specificity.

A Chinese hamster ovary cell is a mammalian cell type widely used in recombinant-protein production. Product glycosylation, assembly and quality depend on the engineered line and culture process.

A membrane contact site closely apposes distinct membranes without fusing them. Demonstrating apposition establishes architecture, while transfer or signaling requires separate functional evidence.

A lipid droplet is a cellular lipid-storage structure. Delivery of an engineered fatty acid into storage can be limited independently of the pathway that synthesizes it.

A chlamydial inclusion is the membrane-bound intracellular compartment supporting chlamydial development. Host trafficking interactions and nutrient access are regulated there.

An elementary body is the infectious form in the chlamydial developmental cycle. Environmental persistence during transmission is distinct from productive extracellular replication.

A reticulate body is the growth-associated form in the chlamydial developmental cycle. genome replication alone does not establish successful production of infectious elementary bodies.

A bacteriocyte is a specialized host cell containing bacterial symbionts. The intracellular environment and transmission route shape selection on both partners.

A cellular phenotype attributable to the affected cell's own genotype or state under the tested conditions. Mosaic experiments distinguish this from effects transmitted through neighbouring cells or the environment.

A proliferative descendant biological population that expands cell output before cell differentiation. The number of divisions and capacity for reversal depend on tissue and context.

Neighbour-dependent selection among cell biological populations in which relatively less-fit cells are lost or displaced. Homogeneous toxicity or slower autonomous growth alone does not establish competitive elimination.

A cardiac muscle cell. Embryonic cell differentiation and contractile activity are compatible with continued proliferation; adult cell-cycle re-entry does not necessarily entail completed division.

Vesicle trafficking moves membrane and cargo between cellular compartments through transport carriers. Cargo selection and budding are followed by targeting, vesicle docking and membrane fusion. A carrier from the endoplasmic reticulum can deliver newly synthesized proteins to the Golgi apparatus, while other carriers retrieve resident components. Directional transport maintains distinct compartments despite continual membrane exchange; it depends on selective recognition rather than random mixing. ^[ref]

An innate cytotoxic lymphocyte whose activation integrates inhibitory and activating signals. Reduced class-I display can remove inhibitory signalling, but is not by itself a universal guarantee of killing.

A stress response is a coordinated change in cellular activity caused by conditions that threaten normal function, such as excessive temperature, nutrient shortage or damaged proteins. It can alter gene expression, protein degradation and metabolism. For example, increased production of molecular chaperones helps handle unfolded proteins. The response is protective only within limits: prolonged or severe stress can cause cell death. Measuring response markers therefore establishes detection of stress, not necessarily successful recovery. ^[ref]

A somatic cell belongs to the body of a multicellular organism rather than its germline. Keratinocytes and cardiomyocytes are examples. The distinction concerns contribution to reproduction rather than a universal difference in chromosome number: many somatic cells are diploid, but specialized exceptions occur. A mutation in a somatic cell can spread through its descendants within the body without necessarily being inherited by offspring. ^[ref]

Cell division partitions a parent biological cell into daughter biological cells. In a typical proliferating eukaryote, DNA replication precedes mitosis, which allocates chromosomes, and cytokinesis separates the cytoplasm. These events can be uncoupled: nuclear division without cytokinesis produces a cell with multiple nuclei. In many bacteria, binary fission instead coordinates chromosome segregation with formation of a new division boundary. ^[ref]

Cell death is irreversible loss of the integrated functions that sustain a biological cell. It can follow catastrophic injury or regulated processes such as apoptosis. Apoptosis typically packages cellular material for removal by other cells; uncontrolled membrane rupture can release intracellular contents. A transient fall in ATP or a single altered marker does not by itself establish irreversible cell death. In development, selective cell death helps shape tissues, illustrating that death of individual cells can serve the organism. ^[ref]

An immune-cell lineage associated with antibody responses. Lineage-specific proliferation and clonal expansion should be distinguished from changes in a mixed sample.

A B cell displays an antigen-binding receptor and can differentiate into an antibody-secreting plasma cell or a memory biological population. Activation selects and expands particular binding specificities, allowing a rare lineage to contribute substantially to an immune response. ^[ref]

Cell viability is the capacity of a biological cell to remain alive under specified conditions. Measurements use operational indicators such as intact cell membranes, metabolic activity or the ability to produce descendants. These indicators answer different questions: a membrane-intact biological cell can be alive yet unable to complete cell division. Consequently, a viability percentage needs an assay definition and a denominator, and should be distinguished from cell proliferation. ^[ref]