Hymenolepis nana

RATIONALE There is evidence that parasitic helminths can ameliorate colitis in animal models and humans. Although infections with Hymenolepis sp. are clinically benign, the immunomodulatory interactions between host and parasite are largely unknown. PATIENT CONCERNS In this study we examined the intestinal mucosa of an adult asymptomatic patient harboring adult and larval dwarf tapeworms (Hymenolepis nana) who underwent surgery for an unrelated reason. INTERVENTIONS Routine histology and immunohistochemistry were performed to characterize the host's response to the parasite. Parasitic DNA was sequenced to identify the tapeworm species. DIAGNOSES Morphological and immunohistochemical studies showed a nearly complete absence of an anti-parasite host immune response. The outer surface of the parasite also showed prominent cross-reactivity with various tested leukocyte antigens. Our findings closely resemble experimentally obtained data from the H. diminuta-infected rat at the state of persistent colonization. OUTCOMES Cross-reactivity of parasite-borne molecules with anti-human-leukocyte antibodies indicates a potential functional role in active modulation of the host's immune response. LESSIONS We believe that better understanding of the host-cestode interaction will certainly extend our knowledge on auto-aggressive disorders such as inflammatory bowel disease and might provide potential treatment options.