Splenic Cellularity and Viability

Splenic cellularity and viability are used as concurrent screens for immunotoxicity. By definition, cellularity is the number of nucleated cells present in an immunocompetent organ. Determination of splenic cellularity is rather insensitive. Cellularity must change by 30% before the effect is considered biologically relevant. The necessity for large weight changes for biological relevance is reflected by a 51% concordance between splenic cellularity and biological effects (Luster etal., 1992a).

A decrease in the viability may suggest an immunotoxic effect within the nucleated cell population. The most common vital stain used to determine viability is trypan blue. Living cells do not take up the dye, but dead or dying cells readily internalize the dye. While trypan blue staining is simple to perform, care must be undertaken to remove extracellular protein from the test sample. Protein in the media leads to false estimates of viability because the dye binds readily to the protein, preventing it from entering dead cells.

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