The extract of Ascaris suum suppresses the humoral and cellular immune responses to unrelated antigens in the mouse. In order to further characterize the suppressive components of A. suum, we produced specific monoclonal antibodies which can provide an important tool for the identification of these proteins. The A. suum immunosuppressive fractions isolated by gel filtration from an extract of adult worms were used to immunize BALB/c mice. Popliteal lymph node cells taken from the immunized animals were fused with SP2/O myeloma cells and the cloned hybrid cells obtained were screened to determine the specificity of secreted antibodies. Three monoclonal antibodies named MAIP-1, MAIP-2 and MAIP-3 were selected and were shown to react with different epitopes of high molecular weight proteins from the A. suum extract.

Summary Helminth infections and parasite components have potent immunomodulatory effects on a host's immune system. In the present study, we investigated the effect of PAS-1, a protein component of Ascaris suum adult worms recognized by a monoclonal antibody (MAIP-1), on humoral and cell-mediated responses to a bystander antigen (ovalbumin [OVA]). MAIP-1 recognized only one of the three polypeptide chains of PAS-1, but neutralized the suppressive effect of the whole worm extract on OVA-specific antibody production. PAS-1 inhibited antibody production against a T-cell-dependent, but not a T-cell-independent, antigen in a dose-dependent way. IgM, IgG 1 , IgG 2b , and also IgE and anaphylactic IgG 1 levels were downregulated. In addition, PAS-1 inhibited OVA-specific delayed type hypersensitivity reactions in the footpad of mice, showing a potent immunosuppressive activity on both Th1 and Th2 responses that seems to be mediated by the induction of large amounts of IL-10 and IL-4. Indeed, PAS-1-specific spleen cells secreted sevenfold more IL-10 and threefold more IL-4 than OVA-specific cells in response to in vitro restimulation with the respective antigens. In conclusion, we showed that PAS-1, a single protein component from A. suum, maintains all its immunosuppressive properties.

The inflammatory and functional changes that occur in murine lung after infection with 2500 infective Ascaris suum eggs were studied in this work. A sequential influx of neutrophils, mononuclear cells and eosinophils occurred into airways concomitantly with migration of larvae from liver to the lungs. Histological analysis of the lung showed a severe intra-alveolar haemorrhage at the peak of larval migration (day 8) and the most intense inflammatory cell infiltrate on day 14. Ascaris L3 were found in alveolar spaces and inside bronchioles on day 8. The number of eosinophils was elevated in the blood on days 8 and 14. The peak of eosinophil influx into the lung was at day 14, as indicated by the high levels of eosinophil peroxidase activity, followed by their migration into the airways. The antibody response against egg and larval antigens consisted mainly of IgG1 and IgM, and also of IgE and anaphylactic IgG1, that cross-reacted with adult worm antigens. Total IgE levels were substantially elevated during the infection. Measurement of lung mechanical parameters showed airway hyperreactivity in infected mice. In conclusion, the murine model of A. suum infection mimics the Th2-induced parameters observed in pigs and humans and can be used to analyse the immunoregulatory properties of this helminth.

Helminth infections have the ability to modulate host's immune response through mechanisms that allow the chronic persistence of the worms in the host. Here, we investigated the mechanisms involved on the suppressive effect of Ascaris suum infection using a murine experimental model of LPS-induced inflammation. We found that infection with A. suum markedly inhibited leucocyte influx induced by LPS into air pouches, suppressed secretion of pro-inflammatory cytokines (IL-1β, TNF-α and IL-6) and induced high levels of IL-10 and TGF-β. Augmented frequency of CD4 CD25 Foxp3 T cells was observed in the mesenteric lymph nodes of infected mice. Adoptive transfer of purified CD4 CD25 T cells to recipient uninfected mice demonstrated that these cells were able to induce a suppressive effect in the LPS-induced inflammation in air pouch model. In addition, adoptive transfer of CD4 CD25 T cells derived from IL-10 knockout mice suggests that this suppressive effect of A. suum infection involves IL-10 cytokine. In conclusion, our results demonstrated that A. suum experimental infection was capable of suppressing LPS-induced inflammation by mechanisms, which seem to be dependent on responses of CD4 CD25 T cells and secretion of IL-10 cytokine.