a). A portion of a scanned cDNA microarray showing the differential expression of perforin in the cDNA microarray. Arrow indicates the position of spots corresponding to perforin (D2). Differential expression is only 3.8 b). Shows the differential expression of perforin in oligonucleotide array. Calculated fold change is 103. (I). Hybridization pattern for the perforin probe set (with RNA isolated from normal PBMC), PM = Perfect match, MM = Mismatch. (II). Hybridization pattern for the perforin probe set (with RNA isolated from leukemic LGL), PM = Perfect match, MM = Mismatch Note: Even though the gene is present in trace amounts in PBMC, it is calculated as absent because of the high background caused by MM hybridization. c). Northern blot showing the expression of perforin. Lane LGL = total RNA obtained from leukemic LGL. Lane N = total RNA isolated from normal healthy individuals. Sample from LGL leukemia patients showed over-expression of perforin.