Data Analysis: What does a histogram tell me?
 The
X-axis is the amount of green fluorescence. The more green fluorescence
a cell emits, the farther to the right the cell data will appear
on the histogram. The Y-axis is the amount of yellow fluorescence.
The more yellow fluorescence a cell emits, the cell data will appear
closer to the top on the histogram.
Quadrant 1 shows data for a cells with many yellow fluorochromes
and no green fluorochromes. Data for cells with high levels of both
yellow and green fluorochromes will appear in quadrant 2. If cells
have neither yellow nor green fluorochromes, the data will appear
in quadrant 3. Data for a cell with many green fluorochromes and
no yellow fluorochromes attached will appear in quadrant 4.
Remember, this histogram only shows CD8+ T-cells, one type of lymphocyte.
Of these types of cells, you are looking for CTLs (cytotoxic
T lymphocytes). The CTLs have a large amount of
Protein Y (yellow fluorochromes) and low amounts of protein G (green
fluorochromes). Where do they appear on the histogram?
Data from the Dioxin Experiment
The CTLs will appear in the boxed upper left quadrant of the histogram.
| This histogram is from a nonimmune mouse,
one that was never injected with tumor cells or exposed to dioxin.
Its immune system has not produced many CTL cells. The flow
cytometer data tells us that the CTL count is about 6% of the
CD8+ T lymphocytes. |
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| This histogram is from a mouse that was injected with tumor
cells called the vehicle control mouse. You
can see that its immune system responded by created a very large
number of CTL cells. In fact, they are 72% of CD8+ T lymphocytes. |
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Let’s take a look at the sample taken from the animal
that was exposed to dioxin one day before it was injected with
the tumor cells.
How does this mouse’s data compare to the two histograms
above? Remember, you know that the mouse was injected with a
tumor cell. Its CTL count is only 8% of CD8+ T lymphocytes.
What is going on?
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