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An autoanti‐Kp b immunoglobulin M that simulates antigen suppression
Author(s) -
Bosco AnnMarie,
Xenocostas Anargyros,
Kinney Jeff,
Cadwell Chantel M.,
Zimring James C.
Publication year - 2009
Publication title -
transfusion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.045
H-Index - 132
eISSN - 1537-2995
pISSN - 0041-1132
DOI - 10.1111/j.1537-2995.2008.02045.x
Subject(s) - antigen , antibody , microbiology and biotechnology , epitope , b cell , immunoglobulin m , antigenicity , biology , serology , immunoglobulin g , flow cytometry , chemistry , immunology
BACKGROUND: Patients may present with an antibody against a blood group antigen, a negative direct antiglobulin test (DAT), and a null phenotype. Typically, this represents an alloantibody in a null individual. However, on occasion, the antibody disappears coincident with conversion to a positive red blood cell (RBC) phenotype. This has been called antigen loss, antigen suppression, or weakened antigenicity. Herein, a unique serologic profile that mimics this pattern, when in fact antigen loss did not occur, is described. STUDY DESIGN AND METHODS: RBCs and serum were analyzed using a gel microtyping system and flow cytometry. Genomic DNA was amplified by polymerase chain reaction and sequenced. RESULTS: Initially, an anti‐Kp b was detected in MTS gel, RBCs typed K−k−Kp(b−), and the DAT was negative for immunoglobulin G (IgG). Later, the anti‐Kp b disappeared and RBCs phenotyped as K−k+Kp(b+). Analysis of initial specimens by flow cytometry identified an immunoglobulin M (IgM) anti‐Kp b with a positive IgM‐specific DAT; eluates contained an anti‐Kp b at immediate spin. Supporting the presence of the Kell glycoprotein, RBCs agglutinated with anti‐Js b . Sequencing showed homozygosity for Kp b with no mutations surrounding the Kp b polymorphism. CONCLUSION: In antigen loss, antibody masking is excluded by a negative DAT. However, because typical DAT reagent does not detect IgM, such reasoning was inaccurate in the current case. In addition, an anti‐Kp b resulted in RBCs typing k−, even though no anti‐k was detected. Overall, this case suggests that an IgM may mask adjacent epitopes and illustrates the potential to mistake a non‐IgG autoantibody as antigen loss.