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Over the past twenty years, DNA analysis has revolutionized forensic science, and has become a dominant tool in law enforcement. Today, DNA evidence is key to the conviction or exoneration of suspects of various types of crime, from theft to rape and murder. However, the disturbing possibility that DNA evidence can be faked has been overlooked. It turns out that standard molecular biology techniques such as PCR, molecular cloning, and recently developed whole genome amplification (WGA), enable anyone with basic equipment and know-how to produce practically unlimited amounts of in vitro synthesized (artificial) DNA with any desired genetic profile. This artificial DNA can then be applied to surfaces of objects or incorporated into genuine human tissues and planted in crime scenes. Here we show that the current forensic procedure fails to distinguish between such samples of blood, saliva, and touched surfaces with artificial DNA, and corresponding samples with in vivo generated (natural) DNA. Furthermore, genotyping of both artificial and natural samples with Profiler Plus((R)) yielded full profiles with no anomalies. In order to effectively deal with this problem, we developed an authentication assay, which distinguishes between natural and artificial DNA based on methylation analysis of a set of genomic loci: in natural DNA, some loci are methylated and others are unmethylated, while in artificial DNA all loci are unmethylated. The assay was tested on natural and artificial samples of blood, saliva, and touched surfaces, with complete success. Adopting an authentication assay for casework samples as part of the forensic procedure is necessary for maintaining the high credibility of DNA evidence in the judiciary system.

International audience; A library of Plasmodium falciparum genomic DNA on the lambda gt11 phage vector was screened for clones positive to a rabbit serum raised against a purified fraction of P. falciparum proteins and a pool of sera from malaria patients. The positive clones were characterized with antibodies purified by the plaque antibody selection technique. This technique consist of purifying specific antibodies on a nitrocellulose filter blotted directly on a lawn of plaques of an antigen-producing phage clone. The purified antibodies are then used as a probe in a Western blot of parasite protein extract, for preliminary characterization of the clones. Using this method, two different clones coding for P. falciparum antigens were identified with the rabbit serum and about 20 with the human sera. This method can be of general use, i.e. it is not limited to parasite systems, and facilitates the immunological analysis and identification of a large number of clones.