Parasitology (1985), 91, 83-99 83 With 5 figures in the text Changes in the surface antigen profile of Schistosoma mansoni during maturation from cercaria to adult worm GILBERTO PAYARES 1 , DIANE J. McLAREN 1 *, W. H. EVANS 2 , andS. R. SMITHERS 1 Divisions of Parasitology 1 and Biochemistry 2 National Institute for Medical Research, Mill Hill, London NWl \AA (Accepted 18 January 1985) SUMMARY Antigenic proteins on the surfaces of different developmental stages of Schistosoma mansoni were radio-iodinated by the Iodogen-catalysed method and identified by immunoprecipitation with a panel of antisera. The sera comprised specific immune serum from mice harbouring a chronic schistosome infection or vaccinated with y-irradiated cercariae; serum from rabbits immunized with adult schistosome tegumental outer membranes or a partially purified M r 32 K glycoprotein from adult worm membranes; and a monoclonal antibody recognizing an M r 20 K antigen on the surface of schistosomula. The M r 38-32 K glycoproteins were the major antigens identified in surface-labelled cercariae and their probable association with the glycocalyx is discussed. Schistosomula transformed from cercariae either mechanically or by penetration of host skin in vitro, expressed a similar pattern of surface antigens to that identified for cercariae, but low molecular weight antigens of M r 20, 17 and 15 K were also detected. The M r 38-32 K glycoproteins, although present on newly transformed schistoso- mula, were progressively replaced with time, by a single dominant glycoprotein (M r 32 K) expressing identical epitopes to those on the M r 38-32 K complex. Moreover, the data confirm that the M r 32 K glycoprotein persists on the tegument after in vivo maturation and is conserved, together with M r 20 and 15 K antigens, through to the adult stage. New antigens (M r 97 and 25 K) were also detected during in vivo maturation and were present in late-stage schistosomes recovered from infected hosts. In addition, the enzyme alkaline phosphatase is expressed on the surfaces of 3-week-old liver worms as a dominant antigen (M r 65 K); this feature may be related to nutritional and/or physiological processes in the tegument of this metabolically active stage of development. INTRODUCTION There is increasing evidence for the pivotal role of surface antigens in regulating the host-parasite interplay. At the molecular level, a number of antigens (M r 38, 32, 20, 17 and 15 K) have been shown to be exposed on the surfaces of newly transformed schistosomula (Dissous, Dissous & Capron, 1981; Simpson, James & Sher, 1983; Knight, Simpson, Payares, Chaudri & Smithers, 1984; Payares, McLaren, Evans & Smithers, 1985) and a modulation of antigen expression has been recognized after in vitro culture of mechanically transformed individuals. These changes include the disappearance of some parasite molecules and the appearance of new parasite antigens that are dependent or independent of the presence of host molecules in the culture medium (Rumjanek, McLaren & Smithers, 1983; Simpson, Payares, Walker, Knight & Smithers, 1984). A few reports have documented differences between the surface antigens of cercariae and mature adult worms (Brink, Krueger & Harris, 1980; Shah & Ramasamy, 1982) but * Reprint requests to Dr J. McLaren.