Sir : In the November 1997 issue of Histopathology, Bussolati et al. describe the restoration of endogenous biotin reactivity following antigen retrieval (using pressure cooking and to a lesser extent microwave retrieval). 1 The authors suggest that blocking of endogenous biotin by sequential avidin-biotin treatment prevents the erroneous detection of biotin.Intra-nuclear biotin inclusions have been previously misinterpreted to be those of Herpes simplex virus (HSV), using the streptavidin-biotin complex (Strep-ABC). 2 We have also described biotin intranuclear inclusions in gestational endometria closely resembling HSV inclusions. 3,4 This error can be easily avoided by paying careful attention to the negative control. We have noted the negative control to be invariably positive, due to the presence of endogenous biotin, with the StrepABC immunodetection system. This false positive immunoreaction should be the clue to the alert pathologist that there is endogenous biotin reactivity. Despite attempts to block endogenous biotin with free avidin and biotin as recommended, 1,5 we have demonstrated residual positivity in the negative control, using the StrepABC system. 4 We have also compared the alkaline-phosphataseanti-alkaline phosphatase (APAAP) and the peroxidaseanti-peroxidase (PAP) detection systems and found that whilst the negative control was negative with the former, there was aberrant immunoreactivity with the PAP system. Curiously this was eliminated with microwave pretreatment prior to immunohistochemistry. 4 These curious results serve to underscore the complexities of antigen retrieval. We use retrieval methods such as pressure cooking, microwave technology and even ultrasound, barely understanding the mechanisms of antigen retrieval. It is inevitable that aberrant and puzzling results are obtained. 6 It is imperative that diagnostic pathologists interpret immunohistochemical findings in the light of positive and negative controls, and also with full knowledge of the pitfalls and limitations of the varying detection systems used in their laboratories.We advocate that the optimal detection system for immunohistochemistry in the tissues containing endogenous biotin, as so comprehensively demonstrated by Bussolati et al. 1 is either the APAAP or PAP immunodetection system (the latter with microwave pretreatment), rather than the StrepABC method. Embarrassing and potentially dangerous errors can thus be avoided.

Different users apply computer forensic systems, models, and terminology in very different ways. They often make incompatible assumptions and reach different conclusions about the validity and accuracy of the methods they use to log, audit, and present forensic data. This is problematic, because these fields are related, and results from one can be meaningful to the others. We present several forensic systems and discuss situations in which they produce valid and accurate conclusions and also situations in which their accuracy is suspect. We also present forensic models and discuss areas in which they are useful and areas in which they could be augmented. Finally, we present some recommendations about how computer scientists, forensic practitioners, lawyers, and judges could build more complete models of forensics that take into account appropriate legal details and lead to scientifically valid forensic analysis.