Evaluation of the potential of excretions-secretions (E-S) of Litomosoides carinii to substitute for human filarial E-S

Immune recognition of Onchocerca volvulus proteins in the human host and animal models of onchocerciasis

Onchocerca volvulus is a tissue-dwelling, vector-borne nematode parasite of humans and is the causative agent of onchocerciasis or river blindness. Natural infections of BALB/c mice with Litomosoides sigmodontis and of cattle with Onchocerca ochengi were used as models to study the immune responses to O. volvulus-derived recombinant proteins (OvALT-2, OvNLT-1, Ov103 and Ov7). The humoral immune response of O. volvulus-infected humans against OvALT-2, OvNLT-1 and Ov7 revealed pronounced immunoglobulin G (IgG) titres which were, however, significantly lower than against the lysate of O. volvulus adult female worms. Sera derived from patients displaying the hyperreactive form of onchocerciasis showed a uniform trend of higher IgG reactivity both to the single proteins and the O. volvulus lysate. Sera derived from L. sigmodontis-infected mice and from calves exposed to O. ochengi transmission in a hyperendemic area also contained IgM and IgG1 specific for O. volvulus-derived recombinant proteins. These results strongly suggest that L. sigmodontis-specific and O. ochengi-specific immunoglobulins elicited during natural infection of mice and cattle cross-reacted with O. volvulus-derived recombinant antigens. Monitoring O. ochengi-infected calves over a 26-month period, provided a comprehensive kinetic of the humoral response to infection that was strictly correlated with parasite load and occurrence of microfilariae.

Does Litomosoides sigmodontis synthesize dimethylethanolamine from choline?

Juvenile female Litomosoides sigmodontis secrete a protein (Juv-p120) highly modified with dimethylethanolamine (DMAE). In an attempt to establish the source of this decoration worms were pulsed with [3H]-choline and [3H]-ethanolamine and the radio-isotope labelled products analysed. Both isotope labels were successfully taken up by the worms, as demonstrated by labelling of phospholipids with [3H]-choline, being predominantly incorporated into phosphatidylcholine and [3H]-ethanolamine into phosphatidylethanolamine. Isotope labelling of phosphatidylethanolamine was particularly striking with the worms taking up approximately 30 times as much labelled ethanolamine as choline. It was possible to detect faint labelling of Juv-p120 with [3H]-ethanolamine after prolonged exposure periods but, unlike the situation with the phospholipids, it was much more readily labelled with [3H]-choline. When pulsing with [3H]-ethanolamine it was also possible to detect isotope-labelled phosphatidylcholine, which may ultimately account for the low levels of labelling of Juv-p120. Overall our results raise the previously unconsidered but intriguing possibility that in L. sigmodontis, choline may be the precursor of DMAE.

Litomosoides sigmodontis in mice: reappraisal of an old model for filarial research

Onchocerciasis and lymphatic filariasis (LF) are major causes of severe morbidity and considerable socio-economic problems throughout the tropics. Vector control and mass chemotherapy have helped to control these infections in some regions, but the temporary success of such measures argues strongly for the development of vaccines. Success in such a venture will require detailed knowledge of protective immune responses in conjunction with the identification of target antigens. By comparison with other important parasitic infections, such as schistosomiasis and leishmaniasis, work on the development of vaccines for onchocerciasis and LF has been constrained because of the difficulties of producing cyclical and patent filarial infection in laboratory mice. Wolfgang Hoffmann and colleagues here outline the opportunities presented by the rodent filaria Litomosoides sigmodontis for filarial research.

Origin, kinetics of circulation and fate in vivo of the major excretory-secretory product of Acanthocheilonema viteae

The excretions-secretions (E-S) of Acanthocheilonema viteae consist mainly of one product, molecular weight 62kDa. This molecule is synthesized during the vertebrate phase of the parasite life-cycle and is first detectable in the E-S of L4 parasites. It is cross-reactive with E-S of human filarial parasites as a consequence of possessing a phosphorylcholine (PC) moiety. The 62 kDa molecule has been employed as a model for the study of the origin and fate of filarial E-S. Immunohistological analysis has shown the molecule to be located predominantly in the parasite gut. Transplantation of adult female [35S] methionine pulsed worms into uninfected jirds resulted in the radio-labelled secreted 62 kDa antigen being detected in the bloodstream within 4 h by SDS-PAGE/immunoprecipitation analysis. The systemic half-life of the molecule as estimated by clearance of injected, purified 125I-labelled material was measured in naive and infected jird hosts. It was reduced from 2-7 h in naive animals to less than 30 min in 4-10 week infected rodents, a finding which correlated with clearance of antigen by antibody in the infected group. In animals infected for longer time periods the serum half-life returned to the values observed in naive jirds. The idea that this change in half-life may reflect differences in the nature of 62 kDa antigen containing circulating immune complexes as infection progresses is discussed. The 125I-labelled antigen is predominantly removed from the circulation via the liver and ultimately excreted in the urine in a non-antigenic form. This work provides the first description of the origin, kinetics of circulation and fate of a defined filarial E-S product and may aid in determining the function and assessing the diagnostic utility of PC-bearing E-S components.