Parasitic organisms are incapable of de novo fatty acid synthesis due to a down-regulated expression of enzymes involved in the oxygen-dependent pathway. We investigated the uptake of host lipids by a 150-kDa hydrophobic ligand-binding protein (HLBP) of Taenia solium metacestode, an agent causative of neurocysticercosis. The protein was found to be a hetero-oligomeric complex consisting of multiple subunits (M(r) 7, 10, and 15 kDa within pH 8.0-9.7), which may originate from four unique genes of 7- and 10-kDa gene families with 2-3 polymorphic alleles/paralogs. The 15-kDa protein represented glycosylated forms of the 10-kDa. With high binding affinity to lipid analogs, these subunits evidenced high-level sequence identity with other cestode HLBPs and form a novel clade associated with excretory-secretory type HLBP. In vitro experiments with viable worms suggested that the excreted 150-kDa protein might bind to lipids, and participate in the translocation of host lipids across the syncytial membrane. This process was substantially inhibited by the specific anti-150 kDa antibodies. The protein was localized in the parasite syncytium and in the lipid droplets within host granuloma wall, where significant lipase activity was expressed. HLBP-mediated uptake of the host lipid may be critical for the parasite survival and thus could be targeted by chemotherapeutics and/or vaccine.

Antigenic proteins of Neospora caninum (N. caninum) against bovine immunoglobulins M, E, A, and G were investigated by using immunoproteomics. Proteins of N. caninum (KBA-2) tachyzoite lysates separated by two-dimensional gel electrophoresis were transferred to polyvinylidene difluoride (PVDF) membranes, probed with different bovine immunoglobulin class and classified. Antigenic spots recognized were also identified by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) analysis. 132, 84, 4, and 40 antigenic protein spots were recognized on N. caninum immunoblot profiles against bovine IgM, IgE, IgA, and IgG, respectively. Of these protein spots, the antigenic proteins recognized by either IgM, IgE, and IgG, or IgM and IgG were HSP70, pyruvate kinase, actin, NCDG-1, tubulin alpha-chain, and putative ribosomal protein S2. On the other hand, IgM, IgE, and IgA reacted with NTPase, HSP60, tubulin beta-chain, putative protein disulfide isomerase, enolase, lactate dehydrogenase, serine-threonine phosphatase, 14-3-3 protein homologue, and GRA2 protein. Most of the antigenic proteins identified were associated with the process of invasion, proliferation, and egression of apicomplexans. In our study, HSP70, actin, NTPase, HSP60, pyruvate kinase, enolase, putative ribosomal protein S2, NCDG-1, and GRA2 proteins were found to be immunodominant proteins, which may contribute to the development of diagnostic markers and vaccine.