Heat maps are one computational tool for comparing gene expression results between multiple experimental samples. The heat map in this figure represents the data for all the transplant patients studied by gene profiles of either kidney transplant biopsies or peripheral blood cells (PBL). The degree of color, ranging from green to red, represents the relative level of gene expression for each gene in each sample. The results for several thousand genes are given here. What is evident simply by looking at the color patterns is that the acute rejection profiles (named AR in the figure) in both the biopsies and PBL are very different than those of the transplants with excellent function (named TX in the figure). This is one part of the evidence that gene expression profiling can be used
diagnostically in transplantation.