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Aim: Many sensitized transplant patients have HLA-specific antibodies due to previous graft failures, blood transfusions, and pregnancies. These humoral responses are typically polyclonal in nature, antibody composition is distinct to each individual, and it is difficult to precisely determine antibody specificity. Distinct antibodies cannot be readily isolated for individual characterization. In this study we isolate distinct anti-HLA antibodies to evaluate their phenotypic and functional traits. Methods: After characterizing sera from highly sensitized patients with a single antigen assay, sera were passed over HLA-specific separation devices made by coupling purified soluble HLA to a sepharose matrix. A scheme of multiple separation rounds involving loading and elution cycles with different HLA allele combinations was applied. This process resulted in mono-specific patterns of HLA reactivity measured by a Luminex-based bead assay. Results: Our results show that complex patterns of sera reactivity can be reduced to more simplified outputs allowing better interpretation of individual antibody populations. Separation of IgG, IgA, and IgM further assisted in the interpretation of these responses. Furthermore, this technique was also of use in evaluating false positive/negative assay signals, strengthening otherwise weak antibody reactivity, and eliminating background interference. Conclusions: Antibody concentration, isotype, epitope specificity, cross-reactivity, and the ability to fix complement have all been implicated as factors that contribute to the pathogenicity of anti-HLA antibodies following organ transplantation. The deconvolution of antibody reactivity patterns can assist in the assessment of risk factors for immunologic rejection as well as provide new insights into anti-HLA antibody profiling and epitope structure analysis. [Copyright &y& Elsevier]

Aim: While it is generally accepted that HLA antibodies represent significant risk factors for transplant rejection and graft failure, it has become apparent that current methodologies are not delivering all the answers to accurately assess transplant patients. Over the years, many controversies and shortcomings have been discussed concerning solid phase antibody detection assays but only a few improvements have been implemented. To better accommodate the increasing demand for more accurate and meaningful data, we set out to develop a new generation of solid phase single antigen assays using soluble HLA. Methods: A single specificity solid phase assay platform was created utilizing 120 soluble HLA alleles and a large panel of control proteins, all of which were validated by qualified monoclonal antibodies. The assays were optimized in regard to sera incubations, wash steps and PE-detection. In some cases, serological specimens were treated using supplemental techniques to reduce sera complexity or remove interference and background problems. Results: In several case studies, more distinctive reaction patterns compared to other assay manufacturers could be demonstrated. The insight into isotype distribution provided helpful facts to draw further conclusions regarding the patient’s immunological state. The usage of soluble HLA demonstrated a higher capacity in sera titration experiments while lack of substantial structural disintegration reduced the false positive rate allowing better definition of single cross-reactive patterns. Conclusions: The complex nature of human sera has set new challenges in the evaluation of the phenotypic and functional traits of antibodies. A large diverse panel of highly purified functionally intact HLA antigens along with a definitive set of control proteins is essential to satisfy the increasing demand for meaningful immunological assessment of transplant patients. [Copyright &y& Elsevier]