Abstract
In outbred (CFLP) and inbred (NIH) mice, the inflammatory response which is thought to be party responsible for the expulsion of Trichinella spiralis from the mid-region of the small intestine, also seemed to be largely responsible fo rthe simulataneous (i.e. early) expulsion of Trichuris muris from the caecum and large intestine during concurrent primary infections. The intractive explusion operated only when the concurrent infections were timed to produce T. Spiralis expulsion before T. muris expulsion would normally occur and the effect persisted for several days after T. Spiralis has been expelled.Interactive expulsion wasss depressed during application of the nonsteroid, anti-inflammatory drug indomethacin and by T-cell expulsion of T. spiralis. These results indicate that a T-cell mediated inflammatory response was probably the basis of the interaction.When the timing of the infections was altered such that the expulsion of T. spiralis there was no reciprocal ecpulsion of the latter. Mice immunized againest one or the other species did not show cross-immunity on heterologus challenge, confirming that the interaction did not involve similar antigens in the two species. The interactive expulsive response is considered as an example of an indirect cross-immunity.