Origin, kinetics of circulation and fate in vivo of the major excretory-secretory product of Acanthocheilonema viteae.

The excretions-secretions (E-S) of Acanthocheilonema viteae consist mainly of one product, molecular weight 62kDa. This molecule is synthesized during the vertebrate phase of the parasite life-cycle and is first detectable in the E-S of L4 parasites. It is cross-reactive with E-S of human filarial parasites as a consequence of possessing a phosphorylcholine (PC) moiety. The 62 kDa molecule has been employed as a model for the study of the origin and fate of filarial E-S. Immunohistological analysis has shown the molecule to be located predominantly in the parasite gut. Transplantation of adult female [35S] methionine pulsed worms into uninfected jirds resulted in the radio-labelled secreted 62 kDa antigen being detected in the bloodstream within 4 h by SDS-PAGE/immunoprecipitation analysis. The systemic half-life of the molecule as estimated by clearance of injected, purified 125I-labelled material was measured in naive and infected jird hosts. It was reduced from 2-7 h in naive animals to less than 30 min in 4-10 week infected rodents, a finding which correlated with clearance of antigen by antibody in the infected group. In animals infected for longer time periods the serum half-life returned to the values observed in naive jirds. The idea that this change in half-life may reflect differences in the nature of 62 kDa antigen containing circulating immune complexes as infection progresses is discussed. The 125I-labelled antigen is predominantly removed from the circulation via the liver and ultimately excreted in the urine in a non-antigenic form. This work provides the first description of the origin, kinetics of circulation and fate of a defined filarial E-S product and may aid in determining the function and assessing the diagnostic utility of PC-bearing E-S components.