Statistical mixture modeling provides an opportunity for automated identification and resolution of cell subtypes in flow cytometric data. The configuration of cells as represented by multiple markers simultaneously can be modeled arbitrarily well as a mixture of Gaussian distributions in the dimension of the number of markers. Cellular subtypes may be related to one or multiple components of such mixtures, and fitted mixture models can be evaluated in the full set of markers as an alternative, or adjunct, to traditional subjective gating methods that rely on choosing one or two dimensions. Four color flow data from human blood cells labeled with FITC-conjugated anti-CD3, PEconjugated anti-CD8, PE-Cy5-conjugated anti-CD4, and APC-conjugated anti-CD19 Abs was acquired on a FACSCalibur. Cells from four murine cell lines, JAWS II, RAW 264.7, CTLL-2, and A20, were also stained with FITC-conjugated anti-CD11c, PE-conjugated anti-CD11b, PE-Cy5-conjugated anti-CD8a, and PE-Cy7-conjugated-CD45R/ B220 Abs, respectively, and single color flow data were collected on an LSRII. The data were fitted with a mixture of multivariate Gaussians using standard Bayesian statistical approaches and Markov chain Monte Carlo computations. Statistical mixture models were able to identify and purify major cell subsets in human peripheral blood, using an automated process that can be generalized to an arbitrary number of markers. Validation against both traditional expert gating and synthetic mixtures of murine cell lines with known mixing proportions was also performed. This article describes the studies of statistical mixture modeling of flow cytometric data, and demonstrates their utility in examples with four-color flow data from human peripheral blood samples and synthetic mixtures of murine cell lines. '
International Society for Advancement of Cytometry
Key termsstatistics; mixture models; Markov chain Monte Carlo; Bayesian analysis; identification; automation; gating ONE of the fundamental uses of flow cytometry is the identification and quantification of distinct cell subsets with phenotypes defined by the density of cell surface or intracellular markers. Ideally, such a biological classification should be objective, stable, and predictive (1).Objectivity, stability, and predictivity are all problematic with the traditional approach in which samples are sequentially gated in one-or two-dimensions. In particular, the choice of which sequence of markers to gate on and where to draw the gates depends on expertise and is highly subjective. This makes it difficult to replicate the cell subset identification procedure across different laboratories. The problem is compounded with polychromatic flow cytometry, because the number of possible gating sequences rises rapidly with the number of channels used. In a recent study of flow cytometric standardization involving 15 institutions, the mean inter-laboratory coefficient of variation ranged from 17 to 44%, even though preparation was standardized and performed using the same samp...