Pyrogen testing revisited on occasion of the 25th anniversary of the whole blood monocyte activation test

The whole blood pyrogen test invented 25 years ago, and its variant based on cryo-preserved blood one year later, brought momentum into the field of pyrogen testing, which, despite the broad application of the Limulus amebocyte lysate (LAL) assay, aka bacterial endotoxin test (BET), consumed several hundred thousand rabbits per year world-wide. The resulting international validation and lengthy acceptance and implementation process of what are called now monocyte activation tests (MATs) finally is impacting on animal numbers - at least in Europe - reducing them by more than 70% and counting. The author sees no reason for continuing any regulatory rabbit testing for pyrogens except the lack of acceptance of MATs in some regions of the world. The availability of MATs has opened also the discussion about the shortcomings of LAL/BET, namely its restriction to Gram-negative pyrogens, non-reflection of the potency of these in humans, interference and masking by many products, and animal welfare concerns for horseshoe crabs. The obvious advantages of MATs in all these respects should lead to a shift from LAL/BET to MATs. We are starting to see this for vac-cines and medical devices, but other areas like safety testing of blood transfusions, cell therapies and nanomaterials, and the assessment of air-borne pyrogens still need to grasp the opportunity provided by MATs. While the different MATs can jointly serve these needs, the whole blood MAT has some advantages as discussed here.