Identification of epitopes of fibronectin attachment protein (FAP-A) of Mycobacterium avium which stimulate strong T-cell responses in mice

Recombinant fusion protein of Heparin-Binding Hemagglutinin Adhesin and Fibronectin Attachment Protein (rHBHA-FAP) of Mycobacterium avium subsp. paratuberculosis elicits a strong gamma interferon response in peripheral blood mononuclear cell culture

Background

Mycobacterium avium subsp. paratuberculosis (MAP) is a causative agent of Johne’s disease in all ruminants worldwide. Economic problems in dairy cattle and sheep industries, public health concern, persistence of MAP in the environment and lack of effective vaccines mentioned necessity of research about various antigens to introduce as vaccine candidates. Based on MAP pathogenesis, it seems that research about the production of new recombinant proteins to stimulate cell-mediated immunity is helpful. This study describes successful expression and purification of a chimeric fusion protein which consists of Heparin-Binding Hemagglutinin Adhesin (HBHA) and high antigenic region of Fibronectin Attachment Protein (FAP-P). Triggered antigen-specific IFN-γ response of isolated PBMCs from immunized goats to rHBHA-FAP and all crude proteins of MAP (PPD), was measured by ELISA.

Results

Significant increases were observed in the IFN-γ production level of peripheral blood mononuclear cells (PBMCs) stimulated by constructed chimeric protein from rHBHA-FAP and PPD vaccinated goats. Antigen-specific gamma interferon (IFN-γ) secretion in positive group (immunized by PPD) against rHBHA-FAP and test group (immunized by rHBHA-FAP) against PPD, also statistically insignificant rises between stimulation with rHBHA-FAP and PPD, suggested the potential and specificity of our chimeric protein to stimulate cell mediated immunity against MAP.

Conclusions

Collectively, these results demonstrate that rHBHA-FAP elicits a strong IFN-γ production in PBMC culture. Therefore, further studies of the present product as a candidate vaccine in naturally infected animals should be conducted, to analyze its potential.

In silico design and expression of a novel fusion protein of HBHA and high antigenic region of FAP-P of Mycobacterium avium subsp. paratuberculosis in Pichia pastoris

Mycobacterium avium subsp. paratuberculosis (MAP) is the etiologic agent of Johne's disease in ruminants and there has been a shift in the public health approach to MAP and human diseases like Crohn's disease. The prevention of infection by MAP in ruminants is thought to deter the high impact of economic losses in the level of dairy industry and possible spreading of this pathogen in dairy products. The present study was done to investigate the construction and expression of the soluble form of a novel fusion protein, consisting of Heparin-binding hemagglutinin (HBHA) and high antigenic region of Fibronectin Attachment Protein-P (FAP-P), in order to introduce as a Th1 inducer subunit vaccine against MAP. HBHA is a mycobacterial adhesin and it has been demonstrated that a HBHA-specific IFN-γ response, in latent M. tuberculosis infection, depends on the methylation of the antigen. Further, FAP-P induces Th1 polarization. Because methylation of HBHA was not performed in E. coli, Pichia pastoris was chosen as the host. The desired fusion protein had a similar 3D structure to that of HBHA with its native form and post-translational methylation in C-terminal. Hence, the uptake of the purified fusion protein will be done by M cells because of HBHA, and cell-mediated immunity will be induced because of both antigens. Eventually, successful construction and expression of the newly-designed chimeric protein under the mentioned conditions is reported in this article.

Cloning and molecular characterization of fibronectin attachment protein gene (ModD) of Mycobacterium avium subspecies paratuberculosis

Fibronectin attachment protein (FAP) also known as ModD gene of 987 bp size was identified in the Mycobacterium avium subsp. paratuberculosis (MAP) genome. This gene was successfully amplified by PCR using specific primers and MAP genomic DNA template, in the presence of 10% DMSO and glycerol. The PCR product was cloned in pGEMT easy cloning vector and subsequently subcloned into pET-33b expression vector and sequenced. MAP ModD gene showed sequence identity ranging from 64 to 94% at nucleotide level and 47-87% at amino acid level, by WU-BLAST program with FAPs of other Mycobacteria species. MAP ModD gene showed 97% sequence homology with M. avium subsp avium ModD by Megalign tool of DNAStar programme. This strong identity was attributed to the more close genetic association of these two species. MAP ModD protein is mainly composed of beta sheets and is highly antigenic. Positive pETModD recombinant clone was induced with IPTG for expression of the ModD protein. The MAP ModD protein was purified under native condition using nickel affinity column. The expressed recombinant ModD (52 kDa) was confirmed by Western blot with nickel-HRPO conjugate and rabbit hyperimmune serum raised against recombinant ModD.

Mycobacterium avium subsp. paratuberculosis fibronectin attachment protein activates dendritic cells and induces a Th1 polarization

Paratuberculosis is a chronic infectious disorder and a major problem in farmed ruminants. This disease is caused by Mycobacterium avium subsp. paratuberculosis. M. avium subsp. paratuberculosis is an important pathogen that causes Johne's disease in animals and also has been implicated as a possible cause of Crohn's disease in humans, but little is known about the protective immune responses to this microorganism. Fibronectin attachment protein (FAP) is a member of a family of fibronectin-binding proteins produced by several species of mycobacteria which is important in the pathogenesis of M. avium. Addition of recombinant FAP to human respiratory tract organ cultures inhibits M. avium binding to areas where there is epithelial damage. We characterized the role of FAP in promoting adaptive and innate immune responses. FAP functionally activated dendritic cells by augmenting the expression of CD80, CD86, major histocompatibility complex class I, and major histocompatibility complex class II. Moreover, FAP induced the allogeneic immunostimulatory capacity of dendritic cells by stimulating dendritic cell production of Th1-promoting interleukin-12. FAP also increased the production of gamma interferon by T cells in mixed-lymphocyte reactions, which would be expected to contribute to the Th1 polarization of the immune response. The expression of surface markers and cytokine production in dendritic cells was mediated by both mitogen-activated protein kinases and NF-kappaB pathways. These results show that FAP modulates the adaptive immune responses to M. avium subsp. paratuberculosis by inducing maturation and activation of dendritic cells, which drives Th1 polarization.

Cloning, expression, purification and serodiagnostic evaluation of fourteen Mycobacterium paratuberculosis proteins

Fourteen proteins of potential diagnostic value for bovine paratuberculosis were identified in the culture filtrate of Mycobacterium paratuberculosis JTC303 by immunoblot and mass spectrometry. The goals of the present study were to express these 14 ORFs in Escherichia coli and evaluate their antigenicity. All 14 proteins were expressed in E. coli BL21(DE3) after transformation with the pET-22b(+) vector. Yields of insoluble proteins were higher than those of the soluble proteins. Polyclonal rabbit antibodies directed against culture filtrate of JTC303 strain confirmed that five of the expressed and purified proteins are culture filtrate components: ModD, Antigen 85C, PepA, MAP1693c, and MAP2168c. Evaluation of ModD as an ELISA solid-phase antigen on a set of bovine sera from well-characterized paratuberculosis cases and infection-free controls revealed that there was strong serum antibody reactivity to rModD in many infected cattle. However, the overall rModD ELISA sensitivity and specificity for bovine paratuberculosis was not greater than those of ELISAs using crude antigens such as cellular extract or culture filtrate for plate coating, as judged by area under the curve (AUC) of Receiver-operating curve (ROC) analysis. However, an ELISA using natural ModD as the solid-phase antigen had a higher sensitivity and AUC than did rModD suggesting diminution of antigenicity in rModD. Taken together, our results showed that the natural forms of the identified proteins may be useful for diagnosis of bovine paratuberculosis.

Identification of mycobacterial surface proteins released into subcellular compartments of infected macrophages

Considerable effort has focused on the identification of proteins secreted from Mycobacterium spp. that contribute to the development of protective immunity. Little is known, however, about the release of mycobacterial proteins from the bacterial phagosome and the potential role of these molecules in chronically infected macrophages. In the present study, the release of mycobacterial surface proteins from the bacterial phagosome into subcellular compartments of infected macrophages was analyzed. Mycobacterium bovis BCG was surface labeled with fluorescein-tagged succinimidyl ester, an amine-reactive probe. The fluorescein tag was then used as a marker for the release of bacterial proteins in infected macrophages. Fractionation studies revealed bacterial proteins within subcellular compartments distinct from mycobacteria and mycobacterial phagosomes. To identify these proteins, subcellular fractions free of bacteria were probed with mycobacterium-specific antibodies. The fibronectin attachment protein and proteins of the antigen 85-kDa complex were identified among the mycobacterial proteins released from the bacterial phagosome.