Synopsis The saliva of blood-feeding parasites is a rich source of peptidase inhibitors that help overcome the host’s defense during host-parasite interactions. Using proteomic analysis, the cystatin OmC2 was demonstrated in the saliva of the soft tick Ornithodoros moubata, an important disease-vector transmitting African swine fever virus and the spirochaete Borrelia duttoni. A structural, biochemical and biological characterization of this peptidase inhibitor was undertaken. Recombinant OmC2 was screened against a panel of physiologically relevant peptidases and found to be an effective broad-specificity inhibitor of cysteine cathepsins, including endopeptidases (cathepsins L and S) and exopeptidases (cathepsins B, C and H). The crystal structure of OmC2 was determined at a resolution of 2.45 Å and used to describe the structure-inhibitory activity relationship. The biological impact of OmC2 was demonstrated both in vitro and in vivo. OmC2 affected the function of antigen-presenting mouse dendritic cells by reducing the production of the proinflammatory cytokines TNF-α and IL-12, and proliferation of antigen-specific CD4+ T cells. This suggests that OmC2 may suppress the host’s adaptive immune response. Immunization of mice with OmC2 significantly suppressed the survival of O. moubata in infestation experiments. We conclude that OmC2 is a promising target for the development of a novel anti-tick vaccine to control O. moubata populations and combat the spread of associated diseases.

SummaryWe have previously demonstrated that two salivary cysteine protease inhibitors from the Borrelia burgdorferi (Lyme disease) vector Ixodes scapularisnamely sialostatins L and L2 -play an important role in tick biology, as demonstrated by the fact that silencing of both sialostatins in tandem results in severe feeding defects. Here we show that sialostatin L2 -but not sialostatin L -facilitates the growth of B. burgdorferi in murine skin. To examine the structural basis underlying these differential effects of the two sialostatins, we have determined the crystal structures of both sialostatin L and L2. This is the first structural analysis of cystatins from an invertebrate source. Sialostatin L2 crystallizes as a monomer with an 'unusual' conformation of the N-terminus, while sialostatin L crystallizes as a domain-swapped dimer with an N-terminal conformation similar to other cystatins. Deletion of the 'unusual' N-terminal five residues of sialostatin L2 results in marked changes in its selectivity, suggesting that this region is a particularly important determinant of the biochemical activity of sialostatin L2. Collectively, our results reveal the structure of two tick salivary components that facilitate vector blood feeding and that one of them also supports pathogen transmission to the vertebrate host.

Ticks developed a multitude of different immune evasion strategies in order to obtain a blood meal. Sialostatin L is an immunosuppressive cysteine protease inhibitor present in the saliva of the hard tick Ixodes scapularis. Herein we demonstrate that sialostatin L strongly inhibits the production of IL-9 by Th9 cells. Since we could show recently that Th9-derived IL-9 is essentially involved in the induction of asthma symptoms, sialostatin L was used for the treatment of experimental asthma. Application of sialostatin L in a model of experimental asthma almost completely abrogated airway hyperresponsiveness and eosinophilia. Our data suggest that sialostatin L can prevent experimental asthma, most likely by inhibiting the IL-9 production of Th9 cells. Thus, alternative to IL-9 neutralization sialostatin L provides the basis for the development of innovative therapeutic strategies to treat asthma.

No abstract

The role of antibodies in the immune response to microsporidiosis was studied using a novel anti-exospore monoclonal antibody (MAb) P5/H1, which recognizes surface antigens of Encephalitozoon cuniculi. The effect of the MAb on microsporidial infection in vivo was to prolong the survival of previously CD4+ reconstituted, perorally infected and intraperitoneally MAb-treated SCID mice. The MAb decreased the numbers of E. cuniculi spores in peritoneal smears obtained post mortem. These results suggest a possible role for antibodies in protection against perorally acquired E. cuniculi infection.

The role of CD4+ and CD8+ T lymphocytes in the protection against intraperitoneally (i.p.) or perorally (p.o.) acquired Encephalitozoon cuniculi (Levaditi et al., C R Soc Biol Paris 89:984-986, 1923) infection was studied by means of reconstitution of severe combined immunodeficiency (SCID) mice with well-defined populations of naive CD8+ or CD4+ T lymphocytes. Adoptive transfer of pure CD8+ T lymphocyte subpopulation protects SCID mice against a lethal microsporidiosis caused by E. cuniculi. The protective effect of CD8+ T lymphocytes is manifested in both i.p. and p.o. infection. On the contrary, the host defense against peroral infection does not require CD8+ T cells. The protective role is not mediated by CD4+ T lymphocytes only. SCID mice reconstitution with pure CD4+ T cell subpopulation led to prolonged survival of perorally infected mice. However, these mice died due to lethal encephalitozoonosis caused by i.p. infection.

The impact of Ixodes ricinus salivary gland extract (SGE) on inflammatory changes in the skin and draining lymph nodes of mice, elicited by the infection with the important human pathogen, B. afzelii, was determined using flow cytometry. SGE injected together with spirochetes reduced the numbers of leukocytes and gammadelta-T lymphocytes in infected epidermis at early time-points post infection. In draining lymph nodes, the anti-inflammatory effect of SGE was manifested by the decrease of total cell count compared with that in mice treated with inactivated SGE. Changes in subpopulations of immunocompetent cells apparently reflected the effect of SGE on the proliferation of spirochetes in the host. The significance of tick saliva anti-inflammatory effect for saliva activated transmission of B. afzelii is shown.

No abstract