Surface proteins of a filarial nematode: a major soluble antigen and a host component on the cuticle of Litomosoides carinii.

The surface composition of three stages in the life cycle of Litomosoides carinii, a filarial parasite of rodents, has been studied using radio-iodination techniques. Confirmation that radiolabelled components were confined to the parasite surface was achieved using light and electron microscope autoradiography. Biochemical analysis of extracts of radiolabelled parasites by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) revealed that one major component (mol. wt. 55 000) could be solubilized with the aid of detergents. This component, which was present on male and female adult worms and on post-parasitic third stage larvae, accounted for about one-third of the total proteins available for surface iodination, and was antigenic in infected hosts. The remaining surface components could be solubilized only with urea and SDS under reducing conditions. The 55 000 mol. wt. surface antigens of male and female adult worms exhibited identical two-dimensional tryptic maps, but the similar 55 000 mol. wt. antigen of post-parasitic third stage larvae was different. There was, however, some sharing of antigenic determinants between adult and larval surface components. The principal protein present in detergent extracts of surface-radio-labelled blood microfilariae was host serum albumin.