| Popis: |
The seminal observation that immunity to Schistosoma mansoni in chronically infected hosts was a form of concomitant immunity prompted the hypothesis that worms of a primary infection survived immune attack by disguising themselves with antigens acquired from the host 34. This in turn implicated the undisguised skin-stage schistosomulum as the likely target of protective resistance 35. In vitro cytotoxicity assays lent credence to this notion, since 3 h schistosomula could be readily ldlled by a v:triety of effector mechanisms in vitro, whereas older worms that had adopted evasive strategies, were refractory 35. Later work using laboratory animals indicated, somewhat surprisingly, that post-skin-stage larvae were subject to immunity in vivo 36, a finding that prompted renewed efforts to identify the true target stage; results of such investigations have tended to confuse rather than clarify the issue, however, particularly with respect to the immunity induced through vaccination with radiation-attenuated cercariae. This article attempts to reconcile conflicting data by showing that schistosonae larvae exhibit a broader window of susceptibility to host immunity than was first anticipated. Acceptance of this concept in turn clarifies other contradictions concerning the sites and mechanisms of protective resistance. |
