Immune response to Trichinella epitopes: the antiphosphorylcholine plaque-forming cell response during the biological cycle.

Phosphorylcholine (PC), an immunodominant component of the cell wall of certain bacteria, fungi and nematodes, is known to induce low anti-PC antibody levels during natural infection by Trichinella spiralis. This article reports a study in which spleen cells from BCF1 mice infected with Trichinella sp. larvae were found to produce large numbers of direct haemolytic plaques in response to PC conjugated to sheep red blood cells (SRBC) after muscle-encysted larvae had been killed by treatment with mebendazole. Inhibition of the response by PC-chloride, immunodiffusion and immunoelectrophoretic studies with the anti-PC IgA (TEPC-15) and anti-idiotype T15 serum assays showed the plaque-forming cell (PFC) response to be specific for PC. The absence of haemolytic plaques when unconjugated SRBC or TNP-SRBC were used as indicator cells ruled out involvement of a polyclonal response. Greatest anti-PC PFC response was found to be associated with a microsomal fraction designated FCp1, a particulate fraction behaving as a thymus-dependent antigen. The FCp1 fractions from all four strains of Trichinella employed induced anti-PC PFC responses when injected into mice. These results suggest that FCp1 is a suitable antigen for use in detailed studies of immune responses to Trichinella and related parasites.