MODEL RELEASED. Tissue compatibility test. Tech- nician using a multi-channel pipette whilst analysing tissues for their compatability and suitability for organ transplants. One such test is for the HL-A (histocompatibility lymphocyte-A) system, an important group of 8 antigens responsible for compatibility of cell membranes in tissues. A high degree of histocompatibility is necessary for tissue grafts and organ transplants to be successful.