Carrier Effect During the Course of Experimental Schistosomiasis: Suppression of the Response to TNP-Schistosomula in Rats and Inbred Mice

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Abstract
The helper T cell response of the mouse and rat to infection with Schistosoma mansoni was measured by using schistosomula as a carrier for the hapten TNP. After infection, both hosts showed a high level of helper T cell activity with a peak response between 8 to 10 days after exposure to cercariae. As infection progressed and protective immunity developed, there was a steady decline in the level of helper T cell activity as detected by the anti-TNP assay, and the response could not be restimulated by a second infection. Mice vaccinated with 30 formalin-fixed schistosomula gave a helper T cell response equivalent to that of infected mice, but their response remained at a high level for at least 24 weeks. Antibody to schistosomula was detected in the serum of mice 5 weeks after infection and reached high titers by week 11; no antibody was detected in vaccinated mice. The passive transfer of serum from 8- to 13-week infected mice reduced the PFC response after injection of TNP-schistosomula in 8- to 10-day infected mice and in vaccinated animals, suggesting that anti-carrier antibody was responsible for the depression of helper T cell activity. IgG purified from the serum of 16- to 17-week infected mice by affinity chromatography with a Sepharose-protein A gel specifically suppressed T cell cooperation to the schistosomular surface. The decline in helper T cell activity in schistosome-infected mice may not indicate a decrease in the number of helper T cells to schistosomula in chronically infected animals, but could reflect the blocking by anti-carrier antibody of the cooperation between T cells and the hapten-committed B cells.