Immunization with the DNA-Encoding N-Terminal Domain of Proteophosphoglycan of Leishmania donovani Generates Th1-Type Immunoprotective Response against Experimental Visceral Leishmaniasis

Abstract

Leishmania produce several types of mucin-like glycoproteins called proteophosphoglycans (PPGs) which exist as secretory as well as surface-bound forms in both promastigotes and amastigotes. The structure and function of PPGs have been reported to be species and stage specific as in the case of Leishmania major and Leishmania mexicana; there has been no such information available for Leishmania donovani. We have recently demonstrated that PPG is differentially expressed in sodium stibogluconate-sensitive and -resistant clinical isolates of L. donovani. To further elucidate the structure and function of the ppg gene of L. donovani, a partial sequence of its N-terminal domain of 1.6 kb containing the majority of antigenic determinants, was successfully cloned and expressed in prokaryotic as well as mammalian cells. We further evaluated the DNA-encoding N-terminal domain of the ppg gene as a vaccine in golden hamsters (Mesocricetus auratus) against the L. donovani challenge. The prophylactic efficacy to the tune of ∼80% was observed in vaccinated hamsters and all of them could survive beyond 6 mo after challenge. The efficacy was supported by a surge in inducible NO synthase, IFN-γ, TNF-α, and IL-12 mRNA levels along with extreme down-regulation of TGF-β, IL-4, and IL-10. A rise in the level of Leishmania-specific IgG2 was also observed which was indicative of enhanced cellular immune response. The results suggest the N-terminal domain of L. donovani ppg as a potential DNA vaccine against visceral leishmaniasis.

Immunoadjuvant Chemotherapy of Visceral Leishmaniasis in Hamsters Using Amphotericin B-Encapsulated Nanoemulsion Template-Based Chitosan Nanocapsules

“…4; see also Fig. S7 in the supplemental material), confirming the reactivity of the J774 cells with splenic MP and consequent Th1-mediated protection (49). The results presented here show that LMW chitosan moderately activated the iNOS pathway in resident MP, as reported previously (50).…”

Visceral Leishmaniasis: Advancements in Vaccine Development via Classical and Molecular Approaches

“…Basu et al (68) and Bhaumik et al (69) utilized KMP-11 for DNA vaccine in hamsters and BALB/c mice, respectively, where they found significant protection with the mixed Th1/Th2 response (surge of IFN-γ, TNF-α, and IL-12 with extreme down-regulation of IL-10). In another study by Samant et al (73), vaccination with DNA-encoding N-terminal domain of the PPG gene in golden hamsters yielded 80% protection against the L. donovani challenge with generation of Th1 type of immune response. Recently, Guha et al (74) showed that immunization with hemoglobin receptor (HbR)–DNA induces complete protection against virulent L. donovani infection in both BALB/c mice and hamsters with an up-regulation of IFN-γ, IL-12, and TNF-α with concomitant down-regulation of IL-10 and IL-4.…”

Elongation Factor-2, a Th1 Stimulatory Protein of Leishmania donovani, Generates Strong IFN-γ and IL-12 Response in Cured Leishmania-Infected Patients/Hamsters and Protects Hamsters against Leishmania Challenge

“…The cycle threshold (CT) value was defined as the number of PCR cycles required for the fluorescence signal to exceed the detection threshold value (background noise). Differences in gene expression were calculated by the comparative CT method (26). This method compares test samples to a comparator sample and uses results obtained with a uniformly expressed control gene (HPRT) to correct for differences in the amounts of RNA present in the two samples being compared with generate a ΔCT value.…”