Cell state and cell function

Question

I have read many papers that refer to cell type, cell state and cell function, but I haven't found an explicit definition for each of these terms.

For example this paper (Brown et al. 1994. J General Virology 75: 2367-2377) refers to cell type and cell state without providing an explicit definition of both terms. I have a vague idea of what these terms mean but a more explicit definition would help me greatly in understanding them.

Answer 1

Mainly cell type refers to the differentiation degree to form a cell population whose characteristics are identifiable by using simple microscopy, stains or immunological methods. Examples of cell types would be T8 lymphocytes, peripheral astrocytes or hepatocytes. Cell types can be pathological too, like tumor cells.

Cell state makes references to the current physiological condition of a given cell. A given cell type can be found in different proliferation states, metabolic conditions (i.e: An adipocyte or a hepatocyte will have different metabolic profiles depending on the insulin and glucagon balance), electrophysiological state (The human oocyte rapidly changes its membrane potential once a spermatozoid has entered) or even degree of differentiation (The typical example are B lymphocytes, which can be in a "naïve" state if they haven't found an antigen, or into a mature state. Once they have matured, thay can be subdivided into cells that actively produce antibodies and cells that divide actively).

A cell function usually refers to a process that occurs inside a cell, or to the physiological function that cell type has in the whole organism. Cell functions could be metabolism, signaling, cell division, etc.; while also could be the likes of detoxification (hepatocytes), hormone production (Langerhans cells) or contraction (myocytes).

Answer 2

I'm busy writing a section on this topic for a dissertation and have run into the following useful definition, which I'll write here for posterity:

• Cell type and state can be thought of as a location in "state space", a virtual landscape covering all possible cell states and types.
• Each point in this space represents a combination of various configurations in the cell: its genomic arrangement (physically and chemically), its transcriptomic profile, its metabolic state, the arrangement of its organelles and cytoplasmic components.
• Configurations which are similar will confer similar functions to cells (having gene expression skewed towards energy production and lysosome formation will probably be associated with phagocytosis, for example). Phagocytic cells thus might be near each other in this space.
• Cell type and state can be thought of as snapshots of this cell space with different resolutions - cell type being a large zoomed out version, and cell state being a granular view. For example, the T lymphocyte cell type is a broad but useful classification of cell, but the cell states within that type could include naïve and activated T lymphocytes.

Some nice references here: an easy blog post by M Bernstein, and a more in-depth article referenced therein by C Trapnell.