The complement interference phenomenon as a cause for sharp fluctuations of serum anti-HLA antibody strength in kidney transplant patients.
The single antigen flow bead (SAFB) assay greatly improves the identification of antigenic specificity of anti-HLA alloantibodies. However, it may underestimate or miss high titer antibodies due to the prozone phenomenon caused by a competition between the fluorescent anti-IgG conjugate and serum complement, for the alloantibody. We explored this effect in our cohort of transplant candidates and transplanted recipients. Among a total of 292 and 269 patients with at least three different sera tested with class I and/or II SAFB assays respectively, we identified 9 patients (6 in class I and 3 in class II) who displayed a profound drop (≥ 75%) followed by a subsequent rise (≥ 100%), in strong (mean fluorescence intensity >8000) antibody levels, across an 18-month period. We postulated that such abrupt fluctuations were not explainable by naturally occurring transient desensitization. Sera were analysed with the SAFB assay using EDTA-treated serum and direct complement C1q staining, and with complement-dependent cytotoxicity and flow cytometry crossmatches (CDCXM and FCXM respectively). The prozone phenomenon was involved in all cases. Because it relies on complement activation, the CDCXM was not sensitive to this phenomenon, but the FCMXM was not either, although it resembles in its principle to the SAFB assay. Four additional anti-human conjugates targeting the IgG Fc fragment or the light chains did not circumvent the SAFB drawback. Therefore, a quick decrease in antibody strength must alert against a potential risk for recipients at the time of the transplant, using virtual crossmatch strategies. A prospective pre-transplant crossmatch still remains an ultimate safeguard.
Laboratoire d'Immunologie et Immunogénétique, Hôpital Pellegrin, CHU de Bordeaux, Bordeaux, France. Electronic address: line-gwenda.guidicelli@chu-bordeaux.fr.
Gwendaline
G
Guidicelli
Guerric
G
Anies
Thomas
T
Bachelet
Valérie
V
Dubois
Jean-François
JF
Moreau
Pierre
P
Merville
Lionel
L
Couzi
Jean-Luc
JL
Taupin
D064591:Allografts; D003165:Complement System Proteins / Q000276:immunology* / Q000378:metabolism; D005260:Female; D005500:Follow-Up Studies; D006680:HLA Antigens / Q000097:blood / Q000276:immunology*; D006650:Histocompatibility Testing; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood / Q000276:immunology*; D007518:Isoantibodies / Q000097:blood / Q000276:immunology*; D016030:Kidney Transplantation; D008297:Male; D012189:Retrospective Studies
D006680:HLA Antigens; D007074:Immunoglobulin G; D007518:Isoantibodies; D003165:Complement System Proteins
CDCXM; Crossmatch; DSA; DTT; EDTA; FCXM; HLA antibody; MCS; MFI; Prozone phenomenon; SAFB; Single antigen flow bead assay; XM; complement-dependent cytotoxicity crossmatch; crossmatch; dithiothreitol; donor-specific antibodies; ethylene diamine tetracetic acid; flow cytometry crossmatch; mean fluorescence channel shift; mean fluorescence intensity; single antigen flow bead; vXM; virtual crossmatch