doi: 10.1111/j.1744-313X.2006.00596.x © 2006 The Authors Journal compilation © 2006 Blackwell Publishing Ltd, International Journal of Immunogenetics 33, 197–200 197 Blackwell Publishing Ltd A single amino acid exchange shifts the serological reactivity of the novel HLA-B*4442 allele product from HLA-B44 to HLA-B21 F. Mrazek,* I. Fae,‡ Z. Ambruzova,* L. Raida,† E. Kriegova,* K. Indrak,† G. F. Fischer‡ & M. Petrek* Summary A novel HLA-B (human leukocyte antigen-B) allele, HLA- B*4442, was identified both in a Czech patient with leu- kaemia and in his mother. The presence of a novel allele was initially suspected because conflicting results were obtained by serological and DNA typing techniques. The HLA typing using the polymerase chain reaction– sequence-specific primers (PCR–SSP) at the two-digit level indicated an allele belonging to the HLA-B*44 group, whereas serological typing indicated HLA-B21. Typing with PCR–sequence-specific oligonucleotides (PCR–SSO) resulted in a unique reaction pattern that could not be assigned to a known allele, PCR–SSP typing at the four-digit level did not match any known B*44 allele, either. The sequencing-based typing of the HLA-B locus then revealed the novel B*4442 allele that is identical with B*4405 except a single C→G nucleotide exchange at position 572. This exchange results in an amino acid substitution from serine to tryptophan at position 167 of the expressed HLA-B protein. The B21 serological reactivity of the novel B*4442 allele product was confirmed by employing an additional serological panel of typing sera. Our findings support pre- vious reports claiming that serine at the position 167 in the alpha-2 domain of the HLA-B protein is a major determinant of the HLA-B44(12) serological epitope. Introduction The human leukocyte antigen (HLA) system is a cluster of extremely polymorphic genes on the short arm of chro- mosome 6 (Marsh et al. , 2005). Due to its fundamental significance for transplantation outcome, the HLA system is one of the most frequently typed genetic systems. Accordingly, the HLA alleles of several million individuals have been typed so far (Bone Marrow Donors Worldwide, httt://www.bmdw.org). Despite such a large population already being typed, novel HLA alleles have been found continually. From a population geneticist’s point of view, novel alleles described at present are usually infrequent (Marsh et al. , 2005). Historically, the definition of HLA polymorphism was based on the definition of HLA antigens using specific antisera (Doxiadis & Claas, 2003). When techniques of molecular genetics extended the HLA-typing methodo- logy, the need for proper correlation between serological and DNA nomenclature arose. For this purpose, ‘HLA dictionaries’ have been established to unify designations of HLA alleles and HLA antigens (Schreuder et al. , 2005). Except physical testing of the serological reactivity of anti- gens associated with particular alleles, methods of bioin- formatics (e.g. neural network) have been introduced to predict serological reactivity of yet undefined allelic HLA products (Maiers et al. , 2003). In general, the serological classification of HLA antigens conforms to groups desig- nated by the first two digits of the allelic nomenclature. Not surprisingly, because serological and DNA tech- niques recognize different levels of HLA polymorphism (epitopes of the HLA molecule vs. genomic DNA sequences), there is a small number of alleles the serolog- ical reactivities of which do not correspond to their classification into the allelic groups according to their nucleotide sequence (Schreuder et al. , 2005). Such ‘dis- crepancies’ are observed most frequently within serologi- cally defined cross-reactive groups of HLA antigens. This applies also for the novel HLA-B*4442 allele. Materials and methods The patient was Caucasoid, his family was of Czech (West Slavonic) ancestry. All available members of the patient’s immediate family (patient, both parents and a brother) were initially typed for the HLA class I (A, B, Cw) anti- Note: the nucleotide sequence of the allele B*4442 reported in this article has been submitted to the EMBL database. Accession number AJ937958 has been assigned to the particular sequence data. The name B*4442 has been officially assigned by the WHO nomenclature committee in May 2005. This follows the agreed policy that, subject to the conditions stated in the most recent nomenclature report (Marsh et al., 2005), names will be assigned to new sequences as they are identified. A list of such new names will be published in the following WHO nomenclature report. * Tissue Typing Laboratory, Department of Immunology and † Department of Haemato-oncology, Medical Faculty, Palacky University, Olomouc, Czech Republic, ‡ Institute for Blood Group Serology, University of Vienna, Vienna, Austria Received 14 January 2006; revised 28 March 2006; accepted 29 March 2006 Correspondence: Frantisek Mrazek, Department of Immunology, Medical Faculty, Palacky University, I.P. Pavlova 6, CZ-775 20 Olomouc, Czech Republic. Tel.: +420 58 5415116; Fax: +420 58 5415116; E-mail: mrazekf@fnol.cz