I have seen the term "mouse LS cell" used in several papers now, but I haven't found an explanation for the origin of these cells (for example, this paper).
What are mouse LS cells? What is their origin (besides coming from mouse!)?
Not an easy question, but I got some references about it. Mouse LS cells are Fibroblasts growing in suspension culture, the paper in reference 1 has this paragraph in its Materials and Methods section:
This cell line seems to be in culture since the 1940s, as the reference to Sanford, Earle and Likely, 1948 suggests. Digging up this reference (number 2 below) tells a bit more about the isolation:
The cells of this study were from Earle's strain L (6), which originated from normal, subcutaneous, connective tissue of an adult C311 strain mouse.
Reference 6 in the Sanford et al. paper is:
EARLE, W. R.: Production of malignancy in vitro. IV. The mouse fibroblast cultures and changes seen in the living cells. J. Nat. Cancer Inst, 4: 165-212 (1943).
which gives no further details. It is a methodic paper which analyzes the conditions necessary for cell culture - interesting on a historical point of view, since the techniques where developed at that time. The full PDF is linked in reference 3.
About the name I need to speculate a bit, but since the original cells where named "Strain L", and LS cells where derived from there to grow in suspension, it might translate into Strain L Suspension cells.