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Background  A family of hydrophilic acylated surface (HASP) proteins, containing extensive and variant amino acid repeats, is expressed at the plasma membrane in infective extracellular (metacyclic) and intracellular (amastigote) stages of Old World  Leishmania  species. While HASPs are antigenic in the host and can induce protective immune responses, the biological functions of these  Leishmania- specific proteins remain unresolved. Previous genome analysis has suggested that parasites of the sub-genus  Leishmania (Viannia)  have lost HASP genes from their genomes.    Methods/Principal Findings  We have used molecular and cellular methods to analyse HASP expression in New World  Leishmania mexicana  complex species and show that, unlike in  L. majo r, these proteins are expressed predominantly following differentiation into amastigotes within macrophages. Further genome analysis has revealed that the  L. (Viannia)  species,  L. (V.) braziliensis,  does express HASP-like proteins of low amino acid similarity but with similar biochemical characteristics, from genes present on a region of chromosome 23 that is syntenic with the HASP/SHERP locus in Old World  Leishmania  species and the  L. (L.) mexicana  complex. A related gene is also present in  Leptomonas seymouri  and this may represent the ancestral copy of these  Leishmania -genus specific sequences. The  L. braziliensis  HASP-like proteins (named the orthologous (o) HASPs) are predominantly expressed on the plasma membrane in amastigotes and are recognised by immune sera taken from 4 out of 6 leishmaniasis patients tested in an endemic region of Brazil. Analysis of the repetitive domains of the oHASPs has shown considerable genetic variation in parasite isolates taken from the same patients, suggesting that antigenic change may play a role in immune recognition of this protein family.    Conclusions/Significance  These findings confirm that antigenic hydrophilic acylated proteins are expressed from genes in the same chromosomal region in species across the genus  Leishmania . These proteins are surface-exposed on amastigotes (although  L. (L.) major  parasites also express HASPB on the metacyclic plasma membrane). The central repetitive domains of the HASPs are highly variant in their amino acid sequences, both within and between species, consistent with a role in immune recognition in the host.

Leishmania-Specific Surface Antigens Show Sub-Genus Sequence Variation and Immune Recognition