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Our previous study showed the efficacy of lactoferrin-monophosphoryl lipid A isolated from Hafnia alvei LPS complex (LF-MPL H.a.) as an adjuvant in stimulation of humoral and cellular immune response in mice to conventional antigens and a lower pyrogenicity of the complex as compared with MPL H.a. alone. In the present investigation we demonstrated that LF-MPL H.a. complex enhanced the immunity of BALB/c mice immunized with Plesiomonas shigelloides CNCTC 138/92 bacterial vaccine, against P. shigelloides infection. The adjuvant effect was evidenced by a significant increase of the antigen-specific serum IgG, IgG2a, and IgG1 and elevation of antigen-specific serum IgA concentrations. In addition, application of the adjuvant facilitated better clearance of the bacteria in spleens and livers of infected mice when compared with MPL H.a. alone. These features of the new adjuvant may predispose it for vaccination protocols in humans.
 The recently identified erythrocyte binding antigen-140 (EBA-140) is a member of the Plasmodium falciparum DBL family of erythrocyte binding proteins, which are considered as prospective candidates for malaria vaccine development. The EBA-140 ligand is a paralogue of the well-characterized P. falciparum EBA-175 antigen. They share homology of domain structure, including Region II, which consists of two homologous F1 and F2 domains and is responsible for ligand-erythrocyte interaction during invasion. It was shown that the F2 domain of EBA-175 antigen seems to be more important for erythrocyte binding. In order to study activity and immunogenicity of EBA-140 antigen F2 domain, it is necessary to obtain recombinant protein of high purity and in a sufficient amount, which used to pose a challenge due to the high content of disulphide bridges. Here, we present a new method for expression and purification of Plasmodium falciparum EBA-140 antigen F2 domain in E. coli Rosetta-gami strain in fusion with the maltose binding protein (MBP). The truncated F2 domain formed by spontaneous proteolytic degradation of the fusion protein was purified by affinity chromatography on Ni-NTA resin followed by size exclusion chromatography. Molecular mass of this protein was confirmed by mass spectrometry. Its N-terminal amino acid sequencing revealed a proteolytic cleavage site within the F2 domain. The proper folding of the recombinant, truncated F2 domain of EBA-140 antigen was confirmed by circular dichroism analysis. The truncated F2 domain can specifically bind to human erythrocytes but its binding is not as efficient as that of full Region II. This confirms that both the F1 and F2 domains of EBA-140 antigen are required for effective erythrocyte binding.
The rough mutants of Gram-negative bacteria are widely used to induce protective antisera but the nature of the target epitope for such antibodies is not precisely de­fined. Endotoxin is one of several antigens present on the surface of bacterial cells, which are able to elicit specific antibodies. We studied the specificity of antibodies produced against a conjugate of E. coli J5 endotoxin core oligosaccharide with tetanus toxoid. The use of chemically defined antigen for immunisation excludes the possibil­ity of production of antibodies against other cell surface antigens. A comparison of this monospecific anti-endotoxin serum with antiserum against E. coli J5 whole cells was performed in order to distinguish the role that endotoxin core oligosaccharide plays in the interaction with humoral host defences from that of other potentially im­portant Gram-negative bacterial surface antigens. The reactivity of both sera with smooth and rough lipopolysaccharides was determined in ELISA, immunoblotting and by flow cytometry. Both antisera reacted with similar specificity with most lipopolysaccharides of identical or related core type. Less distinct reactions with endotoxins of the antibacterial serum in comparison with the anti-conjugate serum were found in all serological tests. LPS of E. coli O100 that showed the strongest reactions with both sera was used to stimulate IL-6, TNFα and nitric oxide production by the J-774A.1 cell line. Both sera were used to inhibit that stimulation and no inhibitory effects of the examined sera in comparison with non-immune serum were observed.
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