Dose dependence of Trichinella spiralis-induced immunopotentiation.

Previous reports studying the immunological and histopathological sequelae following infection with Trichinella spiralis indicated that this nematode can affect the host's immune capability to heterologous antigens. The present investigation was aimed at determining the dose of T. spiralis larvae required for development of maximum delayed-type hypersensitivity (DTH) against heat-killed bacillus Calmette-Guérin (BCG). Mice were injected intraperitoneally with 4 x 10(6) bacteria 28 days after oral intubation with 0, 50, 100, 200, 300 or 400 viable T. spiralis larvae. Groups were tested in vivo for DTH 28 days after administration of nonviable BCG by the footpad swelling assay. Prior infection with 200 nematode larvae resulted in 34 of 42 animals (81%) developing positive 24-hour DTH reactions. When these data were compared to those seen in the other experimental and control groups, the 200 larval dose appeared to effect maximal immunopotentiation in this system.