Persistence Without Pathology in Phosphoglycan-Deficient Leishmania major

Abstract

Leishmania infections involve an acute phase of replication within macrophages, typically associated with pathology. After recovery parasites persist for long periods, which can lead to severe disease upon reactivation. Unlike the role of host factors, parasite factors affecting persistence are poorly understood. Leishmania major lacking phosphoglycans (lpg2-) were unable to survive in sand flies and macrophages, but retained the ability to persist indefinitely in the mammalian host without inducing disease. The L. major lpg2- thus provides a platform for probing parasite factors implicated in persistence and its role in disease and immunity.

Vaccination with Phosphoglycan-Deficient Leishmania major Protects Highly Susceptible Mice from Virulent Challenge without Inducing a Strong Th1 Response

“…We report here that lpg2 Ϫ parasites, which persist without causing overt cutaneous lesions (17), induce protection against virulent challenge in an experimental model, indicating that these parasites might be used as an attenuated vaccine for leishmaniasis.…”

“…Mice infected with lpg2 Ϫ parasites complimented with the LPG2 gene (lpg2 Ϫ/ϩ LPG2) manifested a phenotype similar to those infected with WT parasites, indicating that the inability of lpg2 Ϫ parasites to induce lesion formation was due to a specific lack of LPG2 gene products. However, despite the absence of a lesion, lpg2 Ϫ parasites were recovered from the footpad and draining LN of infected mice at 6 and 10 wk after infection (data not shown) (17).…”

“…This gene encodes the enzyme involved in the transport of GDP mannose to the Golgi for the assembly of disaccharide-phosphate repeats of LPG and other phosphoglycan-containing molecules (18,19). As a result, these parasites fail to synthesize LPG and other surface and secreted phosphoglycans, are highly attenuated in vitro, and upon infection of mice persist for several months without causing any overt cutaneous disease (17). Since these mutant parasites persist without causing any disease (a desirable attribute of a potential attenuated anti-Leishmania vaccine candidate), we investigated the host immune response following infection with lpg2 Ϫ mutants and asked whether these mutants can confer protection against virulent L. major challenge.…”

“…Recently we generated L. major lpg2 Ϫ mutants by targeted deletion of the LPG2 gene (17). This gene encodes the enzyme involved in the transport of GDP mannose to the Golgi for the assembly of disaccharide-phosphate repeats of LPG and other phosphoglycan-containing molecules (18,19).…”

“…major strain LV39 clone 5 promastigotes (Rho/SU/59/P; wild type (WT)), were grown in M199 medium supplemented with 20% FBS, 2 mM L-glutamine, 100 U/ml penicillin, and 100 g/ml streptomycin (complete M199 medium). The homozygous lpg2 Ϫ mutant and parasites complemented with LPG2, termed lpg2 Ϫ/ϩ LPG2, all derived from the WT clone, were generated as previously described and maintained in their respective selective media (17). For infection of mice, parasites were washed three times in PBS and 50 l containing 5 ϫ 10 6 parasites were injected into the right hind footpad.…”