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.
S100A8/S100A9 deficiency increases neutrophil activation and protective immune responses against invading infective L3 larvae of the filarial nematode Litomosoides sigmodontis
