Parasitology and immunology of mice vaccinated with irradiated Litomosoides sigmodontis larvae

L. LE GOFF a1c1, C. MARTIN a1, I. P. OSWALD a2, P. N. VUONG a3, G. PETIT a1, M. N. UNGEHEUER a1 and O. BAIN a1
a1 Institut de Systématique, CNRS-FRS 1541, Biologie Parasitaire, Muséum National d'Histoire Naturelle, 61 rue Buffon, 75231 Paris cedex 05, France
a2 INRA, Laboratoire de Pharmacologie-Toxicologie, 180 chemin de Tournefeuille, BP3, 31931 Toulouse cedex 9, France
a3 Anatomo et Cytopathologie, Hôpital St Michel, 33 rue Olivier de Serres, 75015 Paris, France


This study was performed with Litomosoides sigmodontis, the only filarial species which can develop from the infective larvae to the patent phase in immunocompetent laboratory BALB/c mice. Parasitological features and immune responses were analysed up to 3 months before and after challenge inoculation, by comparing 4 groups of mice: vaccinated challenged, challenged only, vaccinated only, and naive mice. Male larvae were very susceptible to irradiation and only female irradiated larvae survived in vivo. Protection, assessed by a lower recovery rate, was confirmed and was established within the first 2 days of challenge. This early reduction of the recovery rate in vaccinated challenged mice was determined by their immune status prior to the challenge inoculation. This was characterized by high specific IgM and IgG subclass (IgG1, IgG2a and IgG3) levels, high specific IL-5 secretion from spleen cells in vitro and a high density of eosinophils in the subcutaneous connective tissue. Six h after the challenge inoculation, most tissue eosinophils were degranulated in vaccinated challenged mice. Thus, in the protocol of vaccination described, protection appeared mainly to result from the stimulation of a Th2 type response and eosinophils seemed to be the main effectors for the increased killing of infective larvae in vaccinated challenged mice. Two months after challenge inoculation, the percentage of microfilaraemic mice was lower in vaccinated challenged mice as a consequence of this overall reduction in the worm load. In both vaccinated challenged and challenged only groups, the in vitro splenocyte proliferative capacity was reduced in microfilaraemic mice.

(Received July 8 1999)
(Revised October 1 1999)
(Accepted October 4 1999)

Key Words: vaccination; filariae; Litomosoides sigmodontis; immune response; IL-5; eosinophils.

c1 Corresponding author: Ashworth Laboratories, Institute of Cell, Animal and Population Biology, University of Edinburgh, Kings Buildings, Edinburgh EH 9 3JT, UK. Tel: 00 44 131 650 72 89. Fax: 00 44 131 650 54 50. E-mail: