Tissue Typing: Techniques and Importance

JS Dhaliwal

HLA typing and the detection of anti-HLA antibody are used to determine the compatibility of grafts and to test for the presence of preformed antibodies respectively. The Tissue Typing Laboratory at the Institute for Medical Research carries out both these tests to support the bone marrow and solid organ transplant programmes in Malaysia. HLA compatibility is critical in bone marrow transplants. In solid organ transplants however, the presence of preformed antibody is more important in determining the success of the transplant although HLA compatibility does improve the outcome.

At the Institute for Medical Research, HLA typing is carried out using a number of methods including serology, the polymerase chain reaction (PCR) as wells as the bead based fluorescence method. Serological methods are mainly for preliminary screening of donor families and Class I typing. PCR is normally used for Class II testing and confirmation of Class I, while we use the bead based fluorescence method for high throughput HLA typing. Antibody tests include the cross match which detects the presence of donor specific antibodies in the recipient and the panel reactive antibodies (PRA) to determine the reactivity of sera from the recipient against a comprehensive panel of donors.

The cross match is carried using microlymphocytotoxicity and the results are determined by estimating the number of dead cells compared to the positive and negative controls. PRA’s are determined using an ELISA based system as wells as the bead based flow method. These methods give a more consistent and reproducible result than microlymphocytotoxicity which is not as sensitive. Furthermore they detect complement fixing as well as non complement fixing antibody. The flowcytometer cross-match uses fluorescence to detect antibody bound to the cell.