Ivermectin-facilitated immunity in onchocerciasis; activation of parasite-specific Th1-type responses with subclinical Onchocerca volvulus infection

Immunity to a challenge infection of Strongyloides stercoralis third-stage larvae in the jird

Jirds support the entire life-cycle of Strongyloides stercoralis. We therefore used this host as a model to define the mechanism of the immune response to a challenge infection, as well as the parasite stage effected by the response. Jirds given a primary infection of S. stercoralis are resistant to re-infection. The use of implanted diffusion chambers containing larvae showed that the immune response killed the third-stage larvae, and this was confirmed by subcutaneous infections. The larvae of a challenge infection are killed within 48 h, a time period too short to allow for the development of L4 and adult worms. The immune response is dependent on both a serum factor and cells, suggestive of an ADCC type response.

Impact of microfilaremia on maintenance of a hyporesponsive cellular immune response in Brugia-infected gerbils (Meriones unguiculatus)

The purpose of these experiments was to define the significance of the microfilarial stage to the hyporesponsive condition seen in lymphatic filariasis. Two types of experiments were conducted with Brugia pahangi-infected gerbils. In one, in vitro lymphocyte blastogenesis and in vivo granuloma formation in response to parasite antigen were correlated to microfilaremia in chronically infected individuals. In a second set of experiments, the level of in vivo granuloma formation was assessed following chemotherapeutic removal of microfilariae with ivermectin. The results indicated that the microfilarial stage alone is not responsible for the maintenance of the low cellular responses seen during chronic infections in this model. Furthermore, the data suggest that the degree of downregulation of these responses may be related to parasite burden.