Role of amphid in entry of filarial infective larvae to host : especially involvement of odorant

1999 Fiscal Year Final Research Report Summary

• Project/Area Number: 10670233
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 寄生虫学(含医用動物学)
• Research Institution: Nagasaki University
• Principal Investigator: FUJIMAKI Yasunori Institute of Tropical Medicine, Department of Parasitology, Professor, 熱帯医学研究所, 講師 (10209083)
• Co-Investigator(Kenkyū-buntansha): AOKI Yoshiki Institute of Tropical Medicine, Department of Parasitology, Professor, 熱帯医学研究所, 教授 (90039925)
• Project Period (FY): 1998 – 1999
• Keywords: Filaria / Infective larvae / host recognition / amphid / odorant / signal transduction

Research Abstract

Entry of filarial infective larvae to host takes place through the puncture wound caused by the mosquito. Mechanism by which infective larvae find their way to puncture wound is yet uncertain. It has long been recognized that nematodes find and recognize their host, prey or mate by chemotaxis. The filarial infective larvae are also assumed to find the puncture by responding to chemical substances, which come through the mosquito puncture site, and which are recognized by amphid that is considered to be a chemoreceptor whose sensory neuron resemble the primary sensory neurons of the vertebrates olfactory epithelium.
The present study aimed to establish in vitro assay system by which larval behavior to host serum can be observed and evaluated, to find out using the in vitro system, 1) the mechanism by which the larvae recognize the host, 2) whether some odorants in host serum can be attractants for host recognition of the larvae and 3) whether the odorants are detected through signal tran sduction, 4) whether amphid is a receptor which play a role in the response of larvae to serum.
1. Establishment of in vitro assay system : Using 0.6 % agar plate, the in vitro assay system was established in which more than 90 % of larvae migrated towards host serum. Several conditions for the response were required ; 1) larvae should be harvested in Hank's solution, 2) Distilled water should be applied at the opposite side to serum, 3) the response should be done at 27 ℃ Under these conditions the response of larvae occurred regardless of age of larvae.
2. Following results were obtained in the present study using the in vitro assay system mentioned above.
1) Signal transduction pathway is involved in the response of larvae to host serum. That is, ions such as Na^+ and Ca^<2+>, second messengers such as cAMP/cGMP and adenyl cyclase were found to be involved in the response. These findings have never been reported before.
2) The presence of mannose and neuraminidc acid in larvae is at least essential for the reception of the attractive agent from host serum. It was confirmed by the treatment of larvae with enzymes of mannosidase and neuraminidase.
3) Monosaccharides such as glucose, mannose, galactose and fructose changed the host recognizing ability of larvae. These monosaccharides cuased the larvae move outside of the sites of serum, distilled water and inoculation of larvae. This finding has also never been reported before.
4) Filaria larvae did not show a good chemotactic response to all the sera of host (jirds). Less than 50 % of larvae migrated towards some sera. This suggests that there is a difference in existence of attractant(s) or existence of repellent(s) or concentration of attractant(s) between individual sera.
5) The present study, however, could not demonstrate that amphid is a chemosensory involved in host recognition of larvae because the treatment of larvae with a chemical reagent (sodium hypoclorite) which is reported to damage the amphid did not decrease larvae migration towards the host serum.