Evaluation of lung recovery assay for schistosomula in mice immunized with x-irradiated cercariae of Schistosoma mansoni.

The lung recovery assay for schistosomula has recently been used as a rapid method for measuring the state of immunity of a challenged animal. Its merit rests on the fact that the peak day of schistosomular recovery in the lungs of both normal and immune hosts falls on the same day and the degree of immunity can be measured by the percent of schistosomular recovery on this particular day. An evaluation of this method for mice immunized with highly X-irradiated cercariae ofSchistosoma mansoni was made. The results indicate that in the immunized mice the peak day for the schistosomular recovery was delayed and the number of schistosomula recovered on the peak day was decreased. The delay of the peak day was increased by the degree of host immunity, so its identification for a host of an unknown immunologic status was not a simple matter. In addition, this method measured only the immune effect which took place in the skin and on prepeak days in the lungs. It was not as competent as the conventional liver perfusion method which measures the total result of the immune effect of the skin, lungs, and liver. Our conclusion is that for measuring the immunizing effect of irradiated cercariae, the lung recovery method is not suitable for the determination of the state of immunity induced.