Isolation of integral membrane proteins of Leishmania promastigotes and evaluation of their prophylactic potential in hamsters against experimental visceral leishmaniasis

Leishmania donovani triose phosphate isomerase: a potential vaccine target against visceral leishmaniasis

Visceral leishmaniasis (VL) is one of the most important parasitic diseases with approximately 350 million people at risk. Due to the non availability of an ideal drug, development of a safe, effective, and affordable vaccine could be a solution for control and prevention of this disease. In this study, a potential Th1 stimulatory protein- Triose phosphate isomerase (TPI), a glycolytic enzyme, identified through proteomics from a fraction of Leishmania donovani soluble antigen ranging from 89.9–97.1 kDa, was assessed for its potential as a suitable vaccine candidate. The protein- L. donovani TPI (LdTPI) was cloned, expressed and purified which exhibited the homology of 99% with L. infantum TPI. The rLdTPI was further evaluated for its immunogenicity by lymphoproliferative response (LTT), nitric oxide (NO) production and estimation of cytokines in cured Leishmania patients/hamster. It elicited strong LTT response in cured patients as well as NO production in cured hamsters and stimulated remarkable Th1-type cellular responses including IFN-ã and IL-12 with extremely lower level of IL-10 in Leishmania-infected cured/exposed patients PBMCs in vitro. Vaccination with LdTPI-DNA construct protected naive golden hamsters from virulent L. donovani challenge unambiguously (∼90%). The vaccinated hamsters demonstrated a surge in IFN-ã, TNF-á and IL-12 levels but extreme down-regulation of IL-10 and IL-4 along with profound delayed type hypersensitivity and increased levels of Leishmania-specific IgG2 antibody. Thus, the results are suggestive of the protein having the potential of a strong candidate vaccine.

Leishmania donovani: immunostimulatory cellular responses of membrane and soluble protein fractions of splenic amastigotes in cured patient and hamsters

Visceral leishmaniasis (VL), caused by the intracellular parasite Leishmania donovani, L. chagasi and L. infantum is characterized by defective cell-mediated immunity (CMI) and is usually fatal if not treated properly. An estimated 350 million people worldwide are at risk of acquiring infection with Leishmania parasites with approximately 500,000 cases of VL being reported each year. In the absence of an efficient and cost-effective antileishmanial drug, development of an appropriate long-lasting vaccine against VL is the need of the day. In VL, the development of a CMI, capable of mounting Th1-type of immune responses, play an important role as it correlate with recovery from and resistance to disease. Resolution of infection results in lifelong immunity against the disease which indicates towards the feasibility of a vaccine against the disease. Most of the vaccination studies in Leishmaniasis have been focused on promastigote- an infective stage of parasite with less exploration of pathogenic amastigote form, due to the cumbersome process of its purified isolation. In the present study, we have isolated and purified splenic amastigotes of L. donovani, following the traditional protocol with slight modification. These were fractionated into five membranous and soluble subfractions each i.e MAF1-5 and SAF1-5 and were subjected for evaluation of their ability to induce cellular responses. Out of five sub-fractions from each of membrane and soluble, only four viz. MAF2, MAF3, SAF2 and SAF3 were observed to stimulate remarkable lymphoproliferative, IFN-γ, IL-12 responses and Nitric Oxide production, in Leishmania-infected cured/exposed patients and hamsters. Results suggest the presence of Th-1 type immunostimulatory molecules in these sub-fractions which may further be exploited for developing a successful subunit vaccine from the less explored pathogenic stage against VL.

Francisella tularensis T-cell antigen identification using humanized HLA-DR4 transgenic mice

There is no licensed vaccine against the intracellular pathogen Francisella tularensis. The use of conventional mouse strains to screen protective vaccine antigens may be problematic, given the differences in the major histocompatibility complex (MHC) binding properties between murine and human antigen-presenting cells. We used engineered humanized mice that lack endogenous MHC class II alleles but that express a human HLA allele (HLA-DR4 transgenic [tg] mice) to identify potential subunit vaccine candidates. Specifically, we applied a biochemical and immunological screening approach with bioinformatics to select putative F. tularensis subsp. novicida T-cell-reactive antigens using humanized HLA-DR4 tg mice. Cell wall- and membrane-associated proteins were extracted with Triton X-114 detergent and were separated by fractionation with a Rotofor apparatus and whole-gel elution. A series of proteins were identified from fractions that stimulated antigen-specific gamma interferon (IFN-gamma) production, and these were further downselected by the use of bioinformatics and HLA-DR4 binding algorithms. We further examined the validity of this combinatorial approach with one of the identified proteins, a 19-kDa Francisella tularensis outer membrane protein (designated Francisella outer membrane protein B [FopB]; FTN_0119). FopB was shown to be a T-cell antigen by a specific IFN-gamma recall assay with purified CD4(+) T cells from F. tularensis subsp. novicida DeltaiglC-primed HLA-DR4 tg mice and cells of a human B-cell line expressing HLA-DR4 (DRB1*0401) functioning as antigen-presenting cells. Intranasal immunization of HLA-DR4 tg mice with the single antigen FopB conferred significant protection against lethal pulmonary challenge with an F. tularensis subsp. holarctica live vaccine strain. These results demonstrate the value of combining functional biochemical and immunological screening with humanized HLA-DR4 tg mice to map HLA-DR4-restricted Francisella CD4(+) T-cell epitopes.

Selected heavy metals in blood of male Nigerian smokers

Lead, cadmium and zinc levels were determined in the blood of 47 all male smokers (age range, 19-56 years). The subjects were classified into 4 subgroups based on the number of years of smoking, namely: 1-5, 6-10, 11-15 years, >16 years. Thirty all male non-smokers serves as the control. The weight, height and body mass indexes of all subjects were noted in addition to other information obtained through structured questionnaire. Those that were likely to be exposed to any of these metals either occupationally or through other life style habits were excluded from the study. The mean values of blood lead (BPb), blood cadmium (BCd) and blood zinc (BZn) in male smokers (n=47) were 43.26 +/- 4.28, 98.21 +/- 6.39 and 104.84 +/- 3.66 microg dL(-1), respectively while the corresponding mean values for these parameters in the non smokers (n = 30) were 32.44 +/- 3.02, 76.51 +/- 4.59 and 90.38 +/- 2.55 microg dL(-1), respectively. The smokers have statistically significant higher BPb, BCd and BZn than the non-smokers (p < 0.001, p < 0.001 and p < 0.001, respectively). The results appear to confirm the presence of these metals as component of cigarette and agree with similar findings from literature. Consequently, it is probable that high level of these metals in blood of smokers is from tobacco smoking. Additionally it appears that the number of years of smoking has nothing to do with the level of these metals in smokers' blood.

Th1-stimulatory polyproteins of soluble Leishmania donovani promastigotes ranging from 89.9 to 97.1 kDa offers long-lasting protection against experimental visceral leishmaniasis

Our earlier studies identified a fraction (F2) of Leishmania donovani soluble promastigote antigen belonging to 97.4-68 kDa for its ability to stimulate Th1-type cellular responses in cured visceral leishmaniasis (VL) patients as well as in cured hamsters. A further fractionation of F2-fraction into seven subfractions (F2.1-F2.7) and re-assessment for their immunostimulatory responses revealed that out of these, only four (F2.4-F2.7) belonging to 89.9-97.1 kDa, stimulated remarkable Th1-type cellular responses either individually or in a pooled form (P4-7). In this study these potential subfractions were further assessed for their prophylactic potential in combination with BCG against L. donovani challenge in hamsters. Optimum parasite inhibition ( approximately 99%) was obtained in hamsters vaccinated with pooled subfractions and they survived for 1 year. The protection was further supported by remarkable lymphoproliferative, IFN-gamma and IL-12 responses along with profound delayed type hypersensitivity and increased levels of Leishmania-specific IgG2 antibody as observed on days 45, 90 and 120 post-challenge suggesting that a successful subunit vaccine against VL may require multiple Th1-immunostimulatory proteins. MALDI-TOF-MS/MS analysis of these subfractions further revealed that of the 19 identified immunostimulatory proteins, Elongation factor-2, p45, Heat shock protein-70/83, Aldolase, Enolase, Triosephosphate isomerase, Disulfideisomerase and Calreticulin were the major ones in these subfractions.

Reduced nitric oxide synthase 2 (NOS2) promoter activity in the Syrian hamster renders the animal functionally deficient in NOS2 activity and unable to control an intracellular pathogen

Progressive disease in the hamster model of visceral leishmaniasis, caused by Leishmania donovani, in contrast to infection in mice, mimics the progressive disease observed in untreated humans. During progressive infection in hamsters, there was a vigorous type 1 cellular immune response, which is typically associated with control of infection, suggesting that there was ineffective IFN-gamma-mediated macrophage activation. Indeed, at the site of infection, hamsters did not express NO synthase 2 (NOS2), which is the primary mechanism for control of infection in mice. Furthermore, in striking contrast to mouse macrophages, IFN-gamma-activated hamster macrophages did not did not express NOS2 nor generate NO, and were unable to restrict the replication of intracellular L. donovani. The absent hamster NOS2 expression was not the result of NOS2 gene deletion and the NOS2 cDNA had an intact open reading frame. Furthermore, the impaired transcription of NOS2 mRNA was selective and not due to global impairment of IFN-gamma signaling (members of the IFN-gamma-signaling pathway were expressed and functional and IFN-gamma up-regulated several primary and secondary response genes). Strikingly, the proximal hamster NOS2 promoter, like the human ortholog, had >20-fold less basal and IFN-gamma/LPS-inducible activity than the corresponding mouse promoter. Thus, reduced basal and IFN-gamma-induced activity of the hamster NOS2 transcriptional unit, which is unique to this small animal and similar to the human counterpart, accompanies the inability of the animal to control an intracellular pathogen.

Non PC liposome entrapped promastigote antigens elicit parasite specific CD8+ and CD4+ T-cell immune response and protect hamsters against visceral leishmaniasis

Leishmania donovani promastigote soluble antigens (sLAg) were encapsulated in non-phosphatidylcholine (non-PC) liposomes (escheriosomes) prepared from E. coli lipids. The escheriosome-based vaccine was investigated for its potential to elicit a protective immune response against experimental visceral leishmaniasis. The vaccine administration induced strong humoral as well as cell mediated immune responses both in hamsters and BALB/c mice. Immunization of BALB/c mice with escheriosome entrapped sLAg (EL-sLAg) elicited stronger CD8+ cytotoxic T lymphocyte (CTL) response as compared to sLAg entrapped in egg PC/chol liposome (EPC-sLAg) or sLAg administered with incomplete Freund's adjuvant (IFA-sLAg). EL-sLAg also induced the release of mixed (Th1 and Th2) types of cytokines in the immunized BALB/c mice. In addition, the delivery of sLAg via escheriosomes enhanced the expression of costimulatory signals (CD80 and CD86) as determined in peritoneal macrophages obtained from BALB/c mice. In another set of experiments, the EL-sLAg immunized hamsters were found to be better protected than those immunized with EPC-sLAg. The prophylaxis coincided with increased lymphocyte proliferation as well as high nitric oxide (NO) production by peritoneal macrophages among EL-sLAg immunized hamsters. Escheriosomes thus seem to have potential in delivering the antigen to cytosol of the antigen presenting cells (APCs) and in the development of liposome-based vaccine against leishmaniasis as well as other intracellular infections.

Immunostimulatory cellular responses of cured Leishmania-infected patients and hamsters against the integral membrane proteins and non-membranous soluble proteins of a recent clinical isolate of Leishmania donovani

Development of an effective immunoprophylactic agent for visceral leishmaniasis (VL) has become imperative due to the increasing number of cases of drug resistance and relapse. Live and killed whole parasites as well as fractionated and recombinant preparations have been evaluated for vaccine potential. However, a successful vaccine against the disease has been elusive. Because protective immunity in human and experimental leishmaniasis is predominantly of the Th1 type, immunogens with Th1 stimulatory potential would make good vaccine candidates. In the present study, the integral membrane proteins (IMPs) and non-membranous soluble proteins (NSPs), purified from promastigotes of a recent field isolate, Leishmania donovani stain 2001, were evaluated for their ability to induce cellular responses in cured patients (n = 9), endemic controls (n = 5) of visceral leishmaniasis (VL) and treated hamsters (n = 10). IMPs and NSPs induced significant proliferative responses (SI 6.3 +/- 4.1 and 5.6 +/- 2.3, respectively; P < 0.01) and IFN-gamma production (356.3 +/- 213.4 and 294.29 +/- 107.6 pg/ml, respectively) in lymphocytes isolated from cured VL patients. Significant lymphoproliferative responses against IMPs and NSPs were also noticed in cured Leishmania animals (SI 7.2 +/- 4.7 & 6.4 +/- 4.1, respectively; P < 0.01). In addition, significant NO production in response both IMPs and NSPs was also noticed in macrophages of hamsters and different cell lines (J774A-1 and THP1). These results suggest that protective, immunostimulatory molecules are present in the IMP and NSP fractions, which may be exploited for development of a subunit vaccine for VL.