Acanthocheilonema viteae (Dipetalonema viteae)in mice: differences in the relative binding of microfilarial surface-specific antibody may explain the contrasting response phenotypes of BALB/c and C57BL/10

ABSTRACTExperiments were carried out to obtain additional data concerning the role of IgM antibodies, specific for the cuticular surface of the microfilariae (mf) ofA. viteae, in clearing microfilaraemia from high-and low-responder mice infected by transplanted adult worms. Although BALB/c mice, which sustain a chronic microfilaraemia, produced IgM mf surface-specific antibodies, the binding to target mf was weak when compared to that of antibodies from the serum of the resistant C57BL/10 mice. Furthermore, antibodies from BALB/c mice were not as efficient as those from C57BL/10 mice in promoting the adherence of immune or control leukocytes to mfin vitro. Evidence is provided to show that mf shed surface bound antibody. Although the results do not establish conclusively the mechanism underlying the contrasting response phenotypes of C57BL/10 and BALB/c mice, they provide support for the involvement of antibody in controlling microfilaraemia and suggest that quantitative and qualitative differences in the amount and affinity of IgM antibody specific for the mf surface, together with the natural tendency of the mf to shed surface bound antibody at 37°C. may combine to allow the former strain to clear microfilaraemia efficiently whilst the latter sustains a chronic infection.

Radiorespirometric detection of macrofilaricidal activityin vitro

SUMMARYAnin vitromethod for studying radiorespiration has been adapted to single macrofilariae. Using this method viable (but not heat-killed)Dipetalonema viteaeandOnchocera gibsonimacrofilariae evolved measurable amounts of14CO2from L-[U-14C]glutamine. Nonlinear and less uniform rates of14CO2evolution were demonstrated with D-[U-14C]glucose, [1-14C]acetate and [1-14C]octanoate. These findings led us to develop anin vitroscreen in which inhibition of14CO2evolution from L-[U-14C]glutamine was used as a parameter for gauging macrofilaricidal activity. Using this screen we have examined the activity of 17 ‘so-called’ antifilarial standards and found a greater degree of sensitivity than shown by other biochemical criteria. Other data obtained suggest a role for radiorespirometry in determining the viability of fragments ofOnchocerca tissue.

Dipetalonema viteae and Brugia pahangi transplant infections in gerbils for use in antifilarial screening

ABSTRACTTransplanted infections of Dipetalonema viteae and Brugia pahangi have been evaluated as tools for experimental chemotherapy. Attempts were made to establish these filariae in similar pharmacokinetic sites within the same host, so that direct comparisons of in vivo drug susceptibilities could be made. Unfortunately, it was not possible to establish B. pahangi in the subcutaneous tissues, the preferred site of D. viteae. Therefore, intraperitoneal B. pahangi and subcutaneously implanted D. viteae in gerbils were used for the study. D. viteae infections were significantly enhanced by concomitant infections with B. pahangi, while B. pahangi infection rates were unaffected by the presence of D. viteae. Experiments with amoscanate, CGP6140 and Mel W demonstrated the importance of employing both B. pahangi and D. viteae for antifilarial discovery work and the fundamental effect of parasite location on drug efficacy. D. viteae rapidly migrate from the peritoneal cavity of gerbils following implantation; twenty one hours after infection 73% of transplanted worms were found in the subcutaneous tissues. It was shown that the migration response could be used as a stringent parameter for demonstrating antifilarial activity. D. viteae were exposed to antifilarial drugs for 24 hours in vitro, washed and implanted into the peritoneal cavity of gerbils. At autopsy, 5 days later, 10−8M ivermectin and milbemycin D had prevented migration; CGP6140, amoscanate, suramin, flubendazole and furapyrimidone were also detected at <10−6M using this parameter. In all cases the migration response was more sensitive to drugs than parasite kill. Ivermectin's ability to inhibit worm migration through the tissues is discussed, with respect to the role of itinerant males in the reproductive cycle of Onchocerca volvulus.