TISSUE TYPING FOR CLINICAL TRANSPLANTATION
The two main purposes of tissue typing in transplantation are to assess donor-recipient compatibility for HLA and ABO and to analyze patient serum for donor-specific antibody reactivity. For many years the lymphotoxicity technique has been the primary method used to determine HLA type. In this serologic test, lymphocytes are isolated from blood or lymphoid tissues, then incubated with complement-fixing HLA-specific antibodies in microwells. Rabbit complement is added to each well, and any specific antibody that reacts with the HLA antigens expressed on the lymphocyte surface will activate the classical pathway of complement. This leads to cell membran lysis (lymphocytotoxicity), which can be assessed under a microscope by uptake of an extravital dye such as eosin or trypan blue. This method can be used to type for the antigens encoded by the HLA-A, HLA-B and HLA-C loci, and works well with T lymphocytes. HLA-DR and HLA-DQ-encoded antigens are not well expressed on T lymphocytes, and typing for these class II antigens requires an enriched B-lymphocyte preparation or some labeling of B cells in the lymphocyte suspension with a specific antibody. HLA typing takes 4 to 5 hours to perform, and requires four or more 72-well trays with different HLA-specific antibodies.