Sir—The development of a highly sensitive immunoblotting assay to detect PrPSc in various tissues of patients with variant Creutzfeldt-Jakob disease (vCJD), described by J Wadsworth and colleagues (July 21, p 171), 1 is an important step forward in the bid to develop a rapid and sensitive diagnostic test. However, because of a flaw in their methods for preparation of blood cells used in the experiments, their conclusion about the infectivity of peripheral blood buffy coat cells is inaccurate.

Wadsworth and colleagues intended to study the infectivity of peripheral blood buffy coat cells. Yet, for some curious reason, they used mononuclear cells (lymphocytes and monocytes) prepared with Accuspin System Histopaque-1077, excluding granulocytes and platelets. Granulocytes and platelets are the major components of buffy coat preparations—granulocytes account for 60–70% of the peripheral blood leucocytes, and platelet content of buffy coat is about 30–40 times that of total white cells. Therefore, the results obtained in this study are applicable only to peripheral blood mononuclear cells and not buffy coat cells. Thus, unfortunately, the findings of this otherwise excellent work can provide no concrete answers to whether peripheral blood harbours infectivity in vCJD.