nizations have standards for DNA-based HLA typing and an accreditation process (75). For example, extensive guidelines for quality control and quality assurance related to all stages of DNA-based HLA testing are described in the ASHI Standards for HLA Testing (ASHI, http://www.ashihla.org) (1). Additional ASHI guidelines apply for laboratories performing high-volume (>50,000 tests per year) HLA testing (i.e., large-scale registry typing). The ASHI program has accredited over 200 histocompatibility laboratories. The Health Care Financing Administration (HCFA), Joint Commission on Accreditation of Healthcare Organizations (JCAHO), National Marrow Donor Program (NMDP), SouthEastern Organ Procurement Foundation (SEOPF), United Network for Organ Sharing (UNOS); and the states of California, Florida, Oregon, and Washington grant deemed status to ASHI accredited labs.

HLA Assignments—Nomenclature

HLA assignments, testing methods, and reagents were developed through a series of International Histocompatibility Workshops, which began in 1964 and continue today (the 14th workshop is scheduled for December 2005; http://www.microbiol.unimelb.edu.au/micro/14ihiws/). The World Health Organization HLA Nomenclature Committee is responsible for the naming of HLA “types,” and their assignments are included on a web site (http://www.anthonynolan.org.uk/HIG) (50, 69). The names are based on the method of testing used to define HLA “types.” The naming system arose historically so that the nomenclature is difficult to understand.

Testing Methodology—Serology

The first method used for HLA typing was serology, and its use continues today (47). Serology detects different forms of the HLA proteins on the surface of peripheral blood lymphocytes. The assay uses antibodies, predominantly human alloantisera, in a microcytotoxicity assay. The alloantisera are obtained from humans who have been sensitized to HLA antigens by pregnancy or previous transplant. These antibodies are used as reagents to identify serologic specificities (or HLA types). The antibodies react with the HLA molecules present on the cell surface. The serologic specificities of the HLA antigens, HLA-A, -B, -C, -DR, and -DQ can be found on a Web site (http://www.anthonynolan.org.uk/HIG). Antibodies defining HLA-DP antigens are rare, so DP is not identified by serologic typing. Alloantisera are complex reagents containing multiple antibodies; they can react with more than one serologic epitope making interpretation of the results more of an “art.” Most serologic epitopes are thought to lie in the antigen binding region of the HLA molecule.

Each serologic specificity (or HLA type) is designated by a letter indi-



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