Cytokine production in BALB/c mice immunized with radiation attenuated third stage larvae of the filarial nematode, Brugia pahangi.

BALB/c mice immunized with radiation attenuated third stage larvae of the filarial nematode Brugia pahangi are strongly immune to challenge infection. Investigation of the profile of cytokines secreted by spleen cells from immune mice stimulated in vitro with either parasite Ag or with Con A revealed high levels of IL-5 and IL-9 and moderate levels of IL-4. In contrast, secretion of IFN-gamma by spleen cells from immune animals was negligible. Spleen cells from control mice secreted low levels of all cytokines assayed. Levels of parasite-specific IgE were significantly elevated in immune animals and a peripheral blood eosinophilia was observed, which exhibited a biphasic distribution. Our results are consistent with the preferential expansion of Th2 cells in immune animals and provide the basis for dissecting the means by which radiation attenuated larvae of filarial nematodes stimulate immunity.

Attempted vaccination of jirds (Meriones unguiculatus) against Brugia pahangi with radiation attenuated infective larvae.

Jirds were vaccinated by three to five subcutaneous (SC) injections of infective larvae of Brugia pahangi which had been irradiated at 25, 45 or 90 krads from a 60Co source. They were challenged either SC or intraperitoneally. Vaccination with four doses of 50 larvae irradiated with 25 krads produced 49.3% resistance to IP challenge worms and 39.8% against SC challenge worms. Five doses of larvae irradiated with 45 krads produced 62% resistance to SC challenge. Three doses of larvae irradiated with 90 krads produced 74.9% resistance to SC challenge and five doses produced 76.2% resistance. The reasons why irradiated larvae produce resistance whereas normal larvae do not are discussed.

Brugia malayi: vaccination of jirds with 60cobalt-attenuated infective stage larvae protects against homologous challenge.

Vaccination of inbred jirds (Meriones unguiculatus) with 60cobalt radiation-attenuated Brugia malayi infective stage larvae (L3) protected against homologous challenge given either subcutaneously (sc) or by the intraperitoneal (ip) route. Groups of jirds vaccinated once sc with 75, 15 Krad L3 showed from 69% to 91% reduction in recovered worms after ip challenge infection compared to infection in non-vaccinated control jirds, while 75% reduction in mean worm burden was seen in jirds receiving sc challenge infection. A single sc vaccination with 75, 10 or 20 Krad L3 produced no protection (10 Krad) and 64% reduction in recovered worms (20 Krad). Therefore the 15 Krad dose appeared to be best. A marked increase in anti-B. malayi antibody in vaccinated jirds was seen (by ELISA) immediately after challenge infection and an immunofluorescence assay showed that L3 incubated in serum from vaccinated jirds were completely and uniformly covered with specific antibody. Eosinophil-rich granulomas containing dead and moribund L3 were recovered from vaccinated jirds. This model of protective immunity in a Brugia-susceptible small rodent may provide a useful system for identification of molecularly defined filarial-protective immunogens.

Studies with Brugia pahangi. 15. Cobalt 60 irradiation of the worm.

Infective larvae of Brugia pahangi were irradiated at 10, 25 or 45 krads by means of a Cobalt 60 source. In cats, 10 krads caused the worms to be stunted and sterile but allowed them to become 5th stage, migrate posteriorly into the afferent lymphatic, and produce pathology. 25 krads prevented the worms from developing beyond the early fourth stage and from migrating away from the popliteal lymph node. No gross pathological reacions were evident. 45 krads produced the same effects as 25 krads but the longevity of the worms was much reduced.

Studies with Brugia pahangi. 16. Precipitation antibody in infected cats detected by counterimmunoelectrophoresis.

In cats infected with normal, or irradiated, infective (L3) larvae of Brugia pahangi counterimmunoelectrophoresis revealed the presence of antibody to soluble antigens derived from microfilariae, adults and infective larvae of the same parasite. Infected cats with a persistently high to moderate microfilaraemia gave positive precipitin reactions to L3, microfilarial and adult worm antigens. Cats which had become amicrofilaraemic had antibody to L3 and microfilarial antigens but not to adult worm antigen. Serum from cats inoculated with irradiated L3 larvae produced a precipitin reaction only to the L3 antigen.