Proteophosphoglycan functional motifs display genetic polymorphism in a natural population of Leishmania (Viannia) braziliensis.

Abstract

Leishmaniasis causes 3,5M DALYs. Treatment often requires parenteral administration and causes debilitating side effects. Vaccines to prevent the most dramatic outcomes would be most welcome. The Proteophosphoglycan (PPG) is encoded by ppg1 to ppg4 and mediates interaction of Leishmania spp. with macrophages employing two motifs: leucine-rich (LRR), and alanine, proline, and serine repeats (APS). We PCR amplified, cloned, sequenced, and assessed the conservation of LRR and APS of ppg3 and ppg4 in L. braziliensis of 24 patients from Northeast Brazil, then compared them to Leishmania spp. from Genebank. Evolutionary divergencies (ED) between ppg alleles were calculated by Maximum Composite Likelihood. The amplification success of ppg3-lrr was 87.5%; ppg3-aps was 58.3%; and ppg4-lrr was 62.5%. ppg3-lrr presented two conserved alleles of equal frequencies, similar to reference strain's (ED = 0.000). ppg4-lrr presented three alleles with overall lower conservation (ED = 48.820). Conservation was high for two of the alleles (ED = 0.003) present in 87.5% of isolates. Three alleles of ppg3-aps were observed (overall ED = 0.730). One occurred in three L. braziliensis isolates being similar to reference strain's (ED = 0.009). The other two were present in 70% of the isolates, substantially deviating from the reference L. braziliensis (ED > 1.000). Phylogeny employing ppg3-lrr, ppg3-aps or ppg4-lrr clustered L. braziliensis reference and test isolates with the other subgenus Viannia species, segregating them from species of other New and Old-World subgenera. Overall, moderate polymorphism affected functional PPG motifs, opening the possibility of their consideration in eventual subunit vaccines against leishmaniasis.