I was reading an article  where they cultured SEB-1 human sebocytes in DMEM F12 + FBS + EGF + adenine + hydrocortisone + insuline as well as cholera toxin. Why is cholera toxin added to the media? Will the toxin not initiate some kind of unwanted immune response?
Empirically, it can improve growth of cell cultures (https://www.atcc.org/Global/FAQs/C/C/Cholera%20toxin-541.aspx).
It furthermore has the potential to make cell populations more homogeneous by selectively binding to gm1 containing cells that can arise from spatial inhomogeneities among cultured cells. Snijder er al. Nature 2009 (https://www.ncbi.nlm.nih.gov/pubmed/19710653)
A quick check on Wikipedia would have answered your question.
Because the B subunit appears to be relatively non-toxic, researchers have found a number of applications for it in cell and molecular biology. It is routinely used as a neuronal tracer.
Treatment of cultured rodent neural stem cells with cholera toxin induces changes in the localization of the transcription factor Hes3 and increases their numbers.
GM1 gangliosides are found in lipid rafts on the cell surface. B subunit complexes labelled with fluorescent tags or subsequently targeted with antibodies can be used to identify rafts.