Studies of the effect of contralateral versus ipselateral challenge of rats primed on one side with Strongyloides ratti.

The initial pathway of skin penetrating larvae of Strongyloides ratti inside the host is not systemic and could well involve local components of the lymphatic system. The experiments described were an attempt to detect an effect on immunity depending on whether larvae of a challenge infection were committed to a pathway through heavily primed or lightly primed lymph nodes. Female rats were immunised by subcutaneous injection into the right forearm of 10,000 [corrected] heat killed, or 1000 live, third stage larvae of S. ratti. Animals given living parasites were placed on a diet containing 0.1 or 0.2% thiabendazole 48h or 36h after infection. Challenge infections of less than 100 larvae ('exact' doses) were applied on day 21 to either the right or left flank and, similarly, to controls that had received the anthelmintic but not the priming infection. Heat killed parasites elicited no response at all. Priming with live larvae stimulated a significant immunity (16% and 37% depression in 2 experiments), but there was no difference between rats whose challenge was on the same side as the priming dose and those which had the contralateral treatment. The significance of these results to theories of pathfinding in general, and to practical immunology, is discussed.