Characterization of the immune mediator of rapid expulsion of Trichinella spiralis in suckling rats

In order to identify and characterize the mediator(s) of rapid expulsion, infant rats were passively immunized against oral challenge with 200 infectious Trichinella spiralis muscle larvae by oral or intraperitoneal (i.p.) administration of secretions or sera from infected rats. Milk whey from infected dams provided a modest level of protection when fed to pups. Immunoglobulins from T. spiralis-infected rat serum protected suckling pups when injected intravenously (i.v.) into lactating dams 2 days prior to pup challenge. Intraperitoneal injection of pups with serum immunoglobulins also enabled them to express rapid expulsion. The protective component of serum was precipitated with 40% (NH4)2SO4 and was not affected by heating to 56 degrees, although antibodies mediating passive cutaneous anaphylaxis were inactivated by both treatments. Oral transfer of biliary immunoglobulins collected from infected rats at various times during a primary infection provided no protection to pups. However, serum immunoglobulins from rats infected for 42 days or longer transferred rapid expulsion to pups. Absorption of protective serum immunoglobulins with subclass-specific reagents revealed that IgG1 played a significant role in protection.