Adult schistosomes resident in the portal bloodstream feed exclusively on blood. The blind ending alimentary tract comprises a mouth, leading via a short esophagus to the gut where digestion and absorbtion of nutrients takes place. The esophagus has been regarded simply as a conducting tube, although 35 years ago the cluster of cells surrounding the posterior lumen were described as a gland. Recently we showed that in the initial stages of blood processing actually occurred in the esophagus lumen and the first four protein products of the gland, three MEGs and a VAL, have been identified. We now show that in Schistosoma japonicum, at least, the ball of cells surrounding the anterior esophageal compartment also comprises a gland with distinctive vesicular products that are released from the tips of corrugations lining the lumen to interact with incoming blood. We have also undertaken subtractive RNA-Seq to identify the genes that are preferentially expressed in the esophageal region. As a result we have a list of about 30 and the sites of expression of ~10 of these have been confirmed by in situ hybridisation, in both anterior and posterior cell masses. This expands considerably the scope of the molecular mechanisms that may be involved in blood processing. Surprisingly, although transcripts encoding known and new esophageal protein products are present at very high levels, the proteins themselves remain hard to find by proteomic analysis. This makes evaluation of antigenic targets difficult. Furthermore antibody probing of a synthetic peptide array of selected esophageal targets suggests that almost all tested to date are poorly immunogenic. Nevertheless, an induced immune response that targeted the molecules involved in the initial stages of blood feeding remains an attractive proposition.
