Ankylosing spondylitis and related diseases: significance of HL-A W27 histocompatibility antigen.

The HL-A W27 tissue antigen provides a laboratory tool that has already been of great use in explaining the clinical relationships and overlaps among the true seronegative arthritides. In addition, the W27 antigen is useful to the clinician in differential diagnosis and is becoming more readily available through various laboratories. Tissue typing can be done with a tube of blood sent to the laboratory. As and its variants are becoming better understood and thus will be better managed as a result of the recent developments in transplantation antigen typing.