In vitro cultivation of third-stage larvae of Brugia malayi to the young adult stage.

The in vitro cultivation of the filarial nematode Brugia malayi from the infective stage to the fourth and the young adult stage is described. Different culture conditions including cell-free systems and co-culture with different human lymphatic cell lines were compared. Cell-free systems reported by others to promote the in vitro development of the parasites to the adult stage failed to work, i.e. the parasite development stopped at the L4 stage and the larvae died after approximately 3 weeks. Cocultivation with each of the cell lines used enhanced the survival of the parasites. The best results were obtained employing the human T cell leukemia line Jurkat and human dermal fibroblasts as feeder cells in RPMI 1640 supplemented with 10% heat-inactivated human serum. This culture system allowed the cultivation of B. malayi for more than 7 weeks with an average growth of the larvae by factor 6.4 (0.77 +/- 0.035 cm) and a maximum growth by factor 10 (1.2 cm). 69% of the initially cultivated larvae (which corresponded to 100% larvae alive at that time) reached the fourth larval stage after 14 days, and 2.6% of the initially cultivated larvae (which corresponded to 17% of the parasites alive at that day) had reached the young adult stage by day 37 of culture. Parasites remained alive up to 52 days. During the first four weeks of culture, both the length and the periods of moulting of the in vitro cultivated filariae closely resembled those observed with B. malayi in vivo in rodent hosts.