When we were first approached by the senior editors of this series to edit a book on interactions between the host and infectious agents, we acceptedthis offer as an exciting challenge. The only condition, readily agreed upon, was that such a book should focus on the immunology of infections in humans. Our reasons, if not biases, were severalfold. We sensed that the fields of microbiology and im munolgy, which had diverged as each was focusing on its individual search, were coming together. In agreement with the opinions expressed by Dr. Richard Krause in the Introduction, we strongly...