C1q assay for the detection of complement fixing antibody to HLA antigens

Solid phase Luminex(®) and flow cytometric single antigen bead assays offer exquisite sensitivity and specificity for HLA antibody detection. Unlike the historical complement-dependent cytotoxicity (CDC) method, these assays do not distinguish complement fixing from non-complement fixing antibody, the former of which are considered the most clinically relevant in the peri-transplant period. This chapter describes a novel solid phase C1q binding assay to distinguish HLA antibodies that can bind the first component of complement (C1q). These antibodies have the capacity to initiate the complement cascade irrespective of whether that actually occurs. The C1q assay detects many more complement fixing antibodies than are observed by the less sensitive and less specific CDC assay.