Characterization of the genomes of filarial nematodes and of an immunogenic Brugia malayi 70 kilodalton heat shock protein

Abstract

Lymphatic filariasis affects 90 million people worldwide and is caused by the filarial nematodes Wuchereria bancrofti and Brugia malayi. The clinical spectrum of lymphatic filariasis ranges from the normal asymptomatic, amicrofilaremics who comprise greater than 70% of people living in an endemic zone to the hyperimmune patients with tropical pulmonary eosinophilia (TPE) or chronic sequelae of filariasis (ie. elephantiasis) to the seemingly anergic asymptomatic microfilaremic individuals.;Due to the scarcity of parasite material, the filarial nematodes are most easily studied using the techniques of molecular biology. To facilitate these studies, denaturation and renaturation of filarial DNA were analyzed to determine that their DNA is 27-29% guanine and cytosine and 16-18 times more complex than Escherichia coli DNA.;Sera from people exhibiting the various clinical manifestations of lymphatic filariasis were used to screen cDNA libraries from the closely related nematode Onchocerca volvulus to define proteins that may confer immunity to the parasites. One O. volvulus protein which is homologous to 70 kD heat shock protein (hsp70) reacted with many sera from endemic normals, patients with elephantiasis and TPE and with few sera of asymptomatic microfilaremics. The homologous hsp70 gene (Bmhs1) was cloned from B. malayi and sequenced. Northern blot analysis showed that the steady state concentration of the Bmhs1 transcript was induced in infective larvae (L3's) shifted from 25 to 37{dollar}\sp\circ{dollar}C, the temperature shift when moving from mosquito vector to the human host and in adult female worms when shifted from 37 to 42{dollar}\sp\circ{dollar}C. Using an antiserum specific for BmhsA (the protein encoded by Bmhs1) a marked increase in the concentration of BmhsA in heat shocked L3's is demonstrated. In female worms, however, the concentration of BmhsA is not induced by heat shock and BmhsA is primarily expressed in oocytes and 2-8 cell microfilarial embryos. Further study of BmhsA, which is regulated with differentiation in female worms, induced by a physiological temperature change in L3's and primarily reacts with sera of immune individuals living in an endemic zone may provide insight into the regulation of the filarial lifecycle and mechanisms by which human infection may be averted.