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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.
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.
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?

Solve it!