(Go back one page to Requirements for Proper Compensation,
or back to the introduction)
Correct compensation requires the ability to compare a population of cells
stained with only a single color against an unstained population of cells.
In general, this requires n tubes to be set up for compensation,
one for each color, with unstained cells mixed in to the tube after the
cells have been stained and washed.
Alternatively, one could take all of the singly-stained cell samples, and
mix them into a single compensation tube. Now you would end up with n+1
different populations (singly-stained plus one unstained population) for
compensation. Each required compensation would be performed in turn, by
focussing only on the relevantly stained cells and unstained cells.
Another alternative is to stain a single population of cells with antibodies
that would bind to exclusive populations of cells (for instance, in three-color
analysis of peripheral blood lymphocytes, one could use CD19, CD8, and CD4--ignoring
the CD4+CD8+ cells, which are very rare).
These latter two alternatives result in adequate compensation, with the
caveats that the singly-positive cells can be uniquely identified (gated
on), and that the autofluorescence of these populations is all the same.
In using PBL samples, these two criteria are generally met.
However, when performing higher-order compensation (for example, 4 or more
colors), then it becomes highly desirable, if not necessary, to use individual
compensation samples. At a minimum, this is because it can become impossible
to gate uniquely on singly-stained populations when so many dimensions are
involved. But also, it becomes difficult to select this many unique and
exclusively-expressed bright antigens.
An excellent approach (for compensating for PBL experiments) would be to
have CD8 (a very bright antigen) available on every color. Separate tubes
of cells are stained with each different CD8 conjugate and analyzed separately
to set the compensations. CD8 is also a good choice, since there are typically
many CD8-negative (or even CD8-dim) cells against which compensation is
performed.
Go on to examples of 2-color compensation.