Evaluation of the immune response induced in mice by a recombinant form of SPO‐1, a Schistosoma mansoni modulatory protein

Abstract

The S. mansoni tegument (Smteg) represents an important source of antigens to vaccine formulations. However the tegument is also composed of molecules that are involved in the modulation of the host immune system to favour parasite survival. Using immune proteomic tools we have identified proteins from the tegument that were recognized by sera from Smteg‐immunized mice and thus might be involved in the induction of the protective immunity observed in these animals. One of these proteins is SPO‐1, also known as Sm16. This protein has been described as a potent anti‐inflammatory response inducer in the host. The aim of this study was to characterize SPO‐1 expression in the parasite and the immune response trigger by the recombinant form of SPO‐1(rSPO‐1) in mice. To obtain the rSPO‐1, the gene sequence coding for amino acid 23‐90 were sub cloned into the expression vector Pet21a. Escherichia coli BL21 strain were transfected with this construction and the expression was induced using 1mM of Isopropyl β‐D‐1‐thiogalactopyranoside (IPTG). A recombinant protein of approximately 12 kDa fused with a histidine tag was obtained and purified using a niquel column. Using an approved protocol from Brazilian Ethical Committee (LW25/15), Balb‐c mice were immunized with rSPO‐1 and their sera were obtained to be used in Western Blot assay to determine SPO‐1 expression levels through parasite life stage. Protein extracts of the different parasite life stage were also obtained. The results showed that SPO‐1 is mostly expressed in cercariae, 3‐hour schistosomulum and 7‐day schistosomulum. To evaluate the immune response induced in mice by rSPO‐1, 7 mice were intraperitoneally inoculated with 25 μg of rSPO‐1 and one week later their spleen were collected to determine lymphocyte activation status and subtypes. A lower frequency of IL‐10‐producer B cells (p<0.02) and activated CD8+T cells (p<0.02) in SPO‐1‐inoculated animals was observed in comparison to saline‐inoculated mice. Moreover, there was no difference in the frequency of regulatory T cells (CD4+CD25+Foxp3+) or activated CD4+ cells (CD4+CD25+) between groups. An increased percentage of CD4+ cells producing interferon gamma and IL‐4 was observed after in vitro SPO‐1 stimulation in both groups. However, rSPO‐1 was unable to trigger IL‐10 production by CD4 T cells. In conclusion, despite being described in the literature as a regulatory protein, Spo‐1 was unable to induce this profile in the adaptive immunity. Thus, it is important to characterize the effect of SPO‐1 inoculation in myeloid lineage cells.Support or Funding InformationFapemig, CNPq, Capes, CPqRR, Proep/CPqRR