Diagnostic antigens for visceral leishmaniasis: clarification of nomenclatures
© The Author(s). 2017
Received: 13 December 2016
Accepted: 29 March 2017
Published: 13 April 2017
Stimulated by the increasing recent use of ‘K’ or ‘rK’ nomenclature for antigens reported for visceral leishmaniasis (VL) diagnostic serology, we wished to give a chronological synopsis of their reporting and the potentially confusing terminology.
The literature was examined for ‘K' or ‘rK’ terminology for VL diagnostic antigens, with emphasis on the original publications in which terms were first used.
A chronological account of the first use of these 'K' and 'rK' nomenclatures was compiled. Since the original use of this terminology in 1993 in the name rK39 for a Leishmania antigen fragment, we found nine subsequent instances where ‘K' or ‘rK’ have been used to maintain consistency with this nomenclature. We also found instances where there were ambiguities regarding reported strain name, origin and GenBank accession numbers.
We have documented here the uses in the literature of the ‘K’ or ‘rK’ prefix for VL diagnostic antigen nomenclature. We suggest that, to avoid confusion, the use of such nomenclature for future antigens should either provide the logical derivation of the term or indicate that the designation is entirely empirical.
KeywordsLeishmania Visceral leishmaniasis Serology Antigens Kinesin Nomenclature HASPB Diagnostics rK39 rK28
Chronology of the naming of ‘K’ or ‘rK’ antigens used for serological diagnosis of visceral leishmaniasis
GenBank accession number
Burns et al. 
L. infantum (syn. L. chagasi)
Tolson et al. 
Kinetoplastid membrane protein
LD3, derivative of 1S2D clonea
Alce et al. 
MHOM/ET/67/L28 isolate LV9
Bhatia et al. 
L. infantum (syn. L. chagasi)
Hydrophilic protein (see text)
Sivakumar et al. 
Gerald et al. 
Takagi et al. 
Pattabhi et al. 
Abass et al. 
Vallur et al. 
Vallur et al. 
Not applicable; see text.
GenBank searches of sequences homologous to the archetypal diagnostic antigen rK39 identified publications from which the matched sequences were first reported. Publications using subsequent novel rK nomenclature were identified from their listing on NCBI PubMed.
The following year, a previously identified lipophosphoglycan-associated protein in L. donovani entered the literature as KMP-11 (kinetoplastid membrane protein ). We have included this antigen in this review because it has been often reported in the literature, but in this case the K initial was not given to maintain a K nomenclature.
In 1999, Alce et al. reported the identification and antigenicity of two gene products, named HASPB1 and HASPB2 (for hydrophilic acylated surface protein B), from an Ethiopian strain of L. donovani . However, in the same year and the same journal, Bhatia et al. independently reported the characterisation of two hydrophilic antigens, from L. infantum (syn. chagasi), which they named K9 and K26 . There are two crucial considerations regarding the description of these latter two antigens: (i) the authors adopted the letter ‘K’ prefix in order to maintain consistency with K39; (ii) their report also refers to the identification in GenBank of homologous sequences from L. donovani, namely those identified by Alce and colleagues, and thus K9 corresponds to HASPB2, and K26 to HASPB1.
In 2006 and 2007, the first kinesin sequences from South Asian (Indian) and East African (Sudanese) L. donovani (Ld) strains were reported as Ld-rKE16 and LdK39, respectively [6, 7]. Note that the ‘KE’ in Ld-rKE16 refers to the given strain name, and not the two-letter abbreviation for Kenya. The first two 39 amino acid repeats of the Sudanese homologue LdK39 were later incorporated into a synthetic gene, where they were flanked by the repeat sequences of HASPB1 and the whole open reading frame of HASPB2, identified by Alce and colleagues (Fig. 1). This new construct was named rK28, further maintaining the letter K nomenclature of L. donovani antigens useful in diagnostic VL serology, and the prefix ‘r’ denoting a recombinant protein .
The K prefix has also been used for more reported antigens, namely rKRP42 , rKLO8 , rK18  and rKR95 . rKRP42: derived from strain DD8, which was described by the authors as being from Bangladesh but is listed as World Health Organisation (WHO) reference strain MHOM/IN/80/DD8 originating from India [13, 14]. rKLO8: described by the authors as deriving from Sudanese strain Lo8 (lower case letter o) without full WHO code, but a strain with WHO code MHOM/IN/??/Lo8 [sic], had previously been reported also with a lower case letter o but stating an Indian origin . rK18: no sequences or derivations were given. rKR95: identified from mass spectrometry data of Bangladeshi serum and urine and given an accession number (see Table 1). However, searching this number in GenBank (without the sequence identifier prefix ‘GI’) retrieved the entry for LdK39, which was submitted by Gerald et al. 2007 and the sequences of which have been used for the kinesin repeats of rK28 [7, 8].
Our intention here is to document the reporting of VL diagnostic antigens using the letter ‘K’ or ‘rK’ prefix nomenclature. We suggest that, to avoid confusion, the use of such nomenclature for future antigens should either provide the logical derivation of the term, for example, indicating the origin, any known function or protein family or that the designation is entirely empirical.
Hydrophilic acylated surface protein
World Health Organisation
No specific funding was received for this study, however TB has been funded by EC NIDIAG (contract 260260) and TM by the Sir Halley Stewart Trust. The views expressed within this report are those of the authors and not necessarily those of the Trust. TM received a donation towards institutional fees from the John Henry Memorial Fund.
Availability of data and materials
Genomic data referred to herein is publicly available via Genbank https://www.ncbi.nlm.nih.gov/genbank/ using the stated accession numbers.
TB initiated the study. TB and TM wrote and MAM edited the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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