Wuchereria bancrofti 20/22 a homologue of abundant larval transcript L3 stage filarial antigen: molecular and immunological characterization.

The chromadorea abundant larval transcript (ALT) family of proteins contains ALT one of the most studied putative vaccine candidate in experimental filariasis. This study reports the characterization of Wuchereria bancrofti 20/22 (Wb20/22) as a member of chromadorea, the ALT family of proteins from the L3 stage of W. bancrofti. The high reactivity with serum from the endemic normal (EN) population suggests that Wb20/22 could be a target of elicit protective immunity. The glutamic acid-rich region of Wb20/22 was predicted to harbour the longest linear B-cell epitope by insilico prediction tools. The significance of this region was revealed by studying the mutant form of Wb20/22, without acidic domain (WOAD) which was cloned, and the immune response was compared with Wb20/22. The signal sequence of Wb20/22 was also an immunodominant region, and mutant construct without signal sequence (WOSS) was cloned and characterized. The peak antibody titre elicited by WOAD was higher than Wb20/22 or WOSS, which pointed to the immunomodulatory role of glutamic acid-rich region. Wb20/22 elicited very high levels of IL-10 and diminished levels of IL-4 and IL-5 which could be the reason for low antibody titre. The prophylactic efficacy of WOAD conferred protection (62·26%) which was higher than Wb20/22 (49·82%) and WOSS (54·78%).

Immunomodulation of ALT-2 and TLR may collude in antigen specific T cell hyporesponsiveness: proposed mechanism for elevated IL-10 levels in Balb/C mice.

ALT-2, a novel antigen belonging to the chromadorea ALT-2 family of the filarial nematode is proved to clear filarial parasites in Jirds. In order to increase the protection efficacy by stimulating the cell mediated immunity, MPLA a detoxified derivative of LPS known to induce the cellular response, was used in this study as an adjuvant on mice models. ALT-2+MPLA formulation elicited a high titer of total IgG antibody, with profoundly increased levels of IgG2b. Reduced splenocyte proliferation was observed in immunized group when compared to control groups which could be attributed to many in vivo factors. The levels of IFN-γ were high in unstimulated MPLA group compared to ALT-2 stimulated MPLA group, suggesting that the ALT-2 antigen suppressed the IFN-γ levels. A high level of IL-10 was induced by the ALT-2+MPLA formulation, which inhibited the production of Th2 cytokines (IL-4, IL-5) and also reduced the Th1 cytokine (IFN-γ, IL-2) levels which are not in vogue with the classical MPLA adjuvant formulation. We propose a mechanism for this immunomodulation which involves a diminished expression of TLR-4, by which the filarial parasites have evolved to evade host immune mechanism.

Molecular characterization and evaluation of Onchocerca volvulus-secreted larval acidic protein 1 (SLAP1) as a putative vaccine candidate on endemic population of lymphatic filariasis.

Filarial parasites infected nearly 160 million of the global population with onchocerciasis and lymphatic filariasis, and further, a billion of people are estimated to be at risk of infection, rendering them among the most prevalent infectious agents in the world today. Given the complexity of their life cycle and the immune evasion mechanisms of these organisms, development of a vaccine remains to be a long-term challenge. Though a number of immunodominant antigens have been characterized, the presence of homologous proteins in humans or the allelic variants are some of the major drawbacks. One of the extensively studied vaccine candidates is abundant larval transcripts (ALT) family of proteins for the following properties: highly regulated expression, abundance, excreted-secreted product of infective stage larvae, and essentially for parasite establishment and survival in the host. In the present study, stage-specific expression of secreted larval acidic protein 1 (SLAP1) was identified; an ALT orthologue from Onchocerca volvulus was cloned, expressed, and purified as a recombinant protein. Immunogenicity of OvSLAP1 was demonstrated with sera and peripheral blood mononuclear cells from endemic regions of Brugia malayi and Wuchereria bancrofti. OvSLAP1 antibodies were predominated by IgG1 and IgG2 in endemic normal (EN) and chronic pathology (CP) subjects. It has also induced marked cellular response as observed by lymphoproliferation assay. The study revealed that OvSLAP1 can segregate humoral (EN mean optical density (OD) = 0.87 ± 0.035, CP mean OD = 0.59 ± 0.029) and cellular (EN mean stimulation index (SI) = 5.87 ± 0.167, CP mean SI = 3.5 ± 0.134) immune responses between EN and CP individuals (P < 0.001), signifying its prophylactic ability and vitality for protection from filarial infections in endemic population.

Identification of a highly immunoreactive epitope of Brugia malayi TPx recognized by the endemic sera.

Filarial thiordoxin peroxidase is a major antioxidant that plays a crucial role in parasite survival. Although Brugia malayi TPx has been shown to be a potential vaccine candidate, it shares 63% homology with its mammalian counterpart, limiting its use as a vaccine or drug target. In silico analysis of TPx sequence revealed a linear B epitope in the host's nonhomologous region. The peptide sequence (TPx peptide(27-48)) was synthesized, and its reactivity with clinical sera from an endemic region was analyzed. The peptide showed significantly high reactivity (P < 0.05) against the sera of putatively immune individuals compared to the nonendemic control sera. It also showed high reactivity against the sera of patients with chronic pathology and patent infection. The high reactivity of the peptide with endemic immune sera equivalent to that of whole protein shows that it forms a dominant B epitope of TPx protein and thus could be utilized for incorporation into a multiepitope vaccine construct for filariasis.