Restricted sets of parasite antigens from the surface of different stages and sexes of the nematode parasite Nippostrongylus brasiliensis.

Surface molecules of parasitic stages of the nematode Nippostrongylus brasiliensis can be readily iodinated by the chloramine T technique, and assessed for antigenic reactivity with humoral antibody from infected animals. Free-living infective larvae are less amenable to analysis by this, or similar methods, but within 18 hr of larvae entering the host, new macromolecular surface antigens can be detected. The parasites change their surface antigens twice more in the course of the maturation to the adult stage. Surface antigens are stage-specific: lung larvae (L3), intestinal larvae (L4) and gut-living adults each possess characteristic sets of cuticular molecules. Single stage infections result in antibody reactive only to the antigens from the homologous stage. The adult surface appears to bear the greatest number of antigens, one of which is found only on the male worm. The composition of these antigens does not differ grossly between adult worms from a naive or immune host, or worms established after the adaptation of a 'trickle' (multiple low dose) infection. There appears to be an interesting contrast between the rapidity and extent of changes in surface antigens in the early phases of infection, and the stability of adult antigens analysed at different points in the host immune response.