1. Department of Physical Chemistry 2, Lund University, Chemical Centre, P.O. Box 124, S-221 00 Lund, Sweden, Department of Immunotechnology, The Wallenberg Laboratory, Lund University, P.O. Box 7031, S-220 07 Lund, Sweden, Department of Clinical Chemistry, Lund University, University Hospital, Malmö, S-205 02 Malmö, Sweden, and Department of Medicine and Pathology, University of New Mexico, School of Medicine and United Blood Services, Albuquerque, New Mexico 87131-5301