Human serum albumin is a major component on the surface of microfilariae of Wuchereria bancrofti

Wuchereria bancrofi is the major lymphatic filarial parasite of man, and endemic foci are found throughout the tropical zone; as many as 200 million people are currently infected with this nematode (Sasa 1976). Typical of most helminth infections, Bancroftian filariasis is a chronic disease encompassing a wide spectrum of conditions (Nelson 1979, Ottesen 1980) from the otherwise asymptomatic presence of blood microfilariae to the severe state of elephantiasis. Microfilaraemic individuals commonly bear over 1000 nematode larvae per ml of peripheral blood, sustaining no adverse effect from the presence'of this stage of the parasite, which may persist for over 10 years (Carme & Laigret 1979). The immunological basis for the persistence of filarial parasites is poorly understood (Ogilvie & Mackenzie 1981, Piessens 1981, Partono 1982), and studies have been hampered by the strict host-specificity of W . bancrofi (Cross et al. 1981), experimental infection being possible only in Presbytis cristatus monkeys (Palmieri et al. 1982) and other Presbytis species. An initial investigation of the antigenic composition of these parasites was therefore undertaken on the most readily available stage, microfilariae from human blood, using radiolabelling techniques recently reported to define surface components from limited quantities of material (Philipp, Parkhouse & Ogilvie 1980, Parkhouse, Philipp & Ogilvie 1981). We report here that, as in the case of the cotton-rat filarial nematode Litomosoides carinii (Philipp et al. 1984), the most prominent molecule on the surface of these human microfilarial parasites is host serum albumin. Two populations of Wuchereria bancrofti were obtained from separate endemic areas of Bihar State, India, and Jakarta, Indonesia. Both races of parasite display a characteristic nocturnal periodicity (Hawking 1975) and blood samples (20-100 ml) from patients were therefore taken at night. Microfilariae from five individuals in Bihar and one in Jakarta were purified by nucleopore filtration of haemolysed blood (Dennis & Kean 1971) by which parasites are recovered from a 3 pm pore membrane and checked * Present address: Department of Pure and Applied Biology, Imperial College, London SW7 2BR. t Present address: New England Bio-Labs, 32 Tozer Road, Beverly, Massachusetts 01915, USA.