Sarah Peacock, Vasilis Kosmoliaptsis, Andrew J.Bradley and Craig J.Taylor
Luminex single antigen bead (SAB) technology enables highly sensitive and rapid characterization of immunoglobulin G (IgG) human leukocyte antigen (HLA)-specific antibodies. It is widely used to determine antibody compatibility for renal transplantation and to aid the diagnosis of antibody-mediated rejection and response to therapy. HLA-specific antibodies may contribute to allograft rejection through a variety of mechanisms, including activation of the classical complement pathway, endothelial cell activation, and recruitment of Fc-dependent effector cells. Of these, complement-mediated cytotoxicity has long been associated with hyperacute rejection and, more recently, antibody-mediated rejection for which the deposition of the complement component C4d on peritubular capillaries is a diagnostic marker. In the standard SAB assay, patient serum is incubated with microbeads coated with purified HLA proteins. Human leukocyte antigenYspecific IgG antibody binding is then detected using a fluorescent anti-IgG detection antibody. Increasing levels of donor HLA-specific antibodies detected by this assay predict inferior long-term graft outcome, but not all patients with IgG donor-specific HLA antibodies (DSA) have a poor graft outcome (1,2). This observation is consistent with the notion that HLA antibodies with the same specificity may differ in their ability to cause graft injury, and this variability may be related to differences in complement fixing activity.