Li XH, Xu YX, Vance G, Wang Y, Lv LB, van Dam GJ, Cao JP, Wilson RA. Evidence That Rhesus Macaques Self-Cure from a Schistosoma japonicum Infection by Disrupting Worm Esophageal Function: A New Route to an Effective Vaccine?
PLoS Negl Trop Dis 2015;
9:e0003925. [PMID:
26161644 PMCID:
PMC4498593 DOI:
10.1371/journal.pntd.0003925]
[Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Accepted: 06/19/2015] [Indexed: 12/14/2022] Open
Abstract
Background
Rhesus macaques are unusual among schistosome hosts, self-curing from an established infection and thereafter manifesting solid immunity against a challenge, an ideal model for vaccine development. Previously, the immunological basis of self-cure was confirmed; surviving worms had ceased feeding but how immunological pressure achieved this was unclear. The schistosome esophagus is not simply a conduit for blood but plays a central role in its processing. Secretions from the anterior and posterior esophageal glands mix with incoming blood causing erythrocyte lysis and tethering and killing of leucocytes.
Methodology/Principal Findings
We have analysed the self-cure process in rhesus macaques infected with Schistosoma japonicum. Faecal egg output and circulating antigen levels were used to chart the establishment of a mature worm population and its subsequent demise. The physiological stress of surviving females at perfusion was especially evident from their pale, shrunken appearance, while changes in the structure and function of the esophagus were observed in both sexes. In the anterior region electron microscopy revealed that the vesicle secretory process was disrupted, the tips of lining corrugations being swollen by greatly enlarged vesicles and the putative sites of vesicle release obscured by intense deposits of IgG. The lumen of the posterior esophagus in starving worms was occluded by cellular debris and the lining cytoplasmic plates were closely adherent, also potentially preventing secretion. Seven proteins secreted by the posterior gland were identified and IgG responses were detected to some or all of them. Intrinsic rhesus IgG colocalized with secreted SjMEGs 4.1, 8.2, 9, 11 and VAL-7 on cryosections, suggesting they are potential targets for disruption of function.
Conclusions/Significance
Our data suggest that rhesus macaques self-cure by blocking esophagus function with antibody; the protein products of the glands provide a new class of potential vaccine targets.
Rhesus macaques can self-cure from a schistosome infection. Antibody is crucial to drive this process and adult worm elimination is preceded by cessation of blood feeding. Recently we have shown that the schistosome esophagus plays a central role in blood processing. We first confirm the self-cure process in rhesus macaques infected with Schistosoma japonicum and provide evidence that the self-cure mechanism involves blocking the worm esophagus function with antibody. In the anterior region, secretion of light vesicles is disrupted hence their contents are not released into the lumen to interact with blood components to fulfil their tasks. The plates in the posterior lining stick together whilst the lumen is occluded, hampering blood processing. Furthermore, rhesus IgG binds strongly to the worm esophageal lumen and co-localizes completely with five esophageal secreted proteins, SjMEGs 4.1, 8.2, 9, 11 and VAL-7. Our results indicate that rhesus macaques eliminate their adult worms by disrupting esophageal function making blood difficult to ingest; feeding stops eventually causing their demise because nutrient uptake across the body surface cannot fully compensate.
Collapse