Resistance of mice to secondary infection with Schistosoma japonicum, with special reference to neutrophil enriched response to schistosomula in the skin of immune mice.

The lung recovery assay for schistosomula has been used as a rapid method for measuring acquired resistance to Schistosoma mansoni infection in challenged animals. This assay method was successfully utilized in the present study with S. japonicum in mice. Assay of resistance to reinfection with the lung recovery technique and with the conventional perfusion method demonstrated that a considerable level of resistance developed in mice which had received the primary infection of 30 S. japonicum cercariae 8 weeks prior challenge infection. In a histological study of this period, as early as 4 hours after challenge exposure there was already a dense accumulation of cells around a small proportion of schistosomula in the immune mouse skin. Light and electron microscopy revealed that the adherent cells were mainly neutrophils. There was a more increase in the cellular reaction around the schistosomula in the skin 24 hours after challenge and the cells of this reaction were still predominantly neutrophils with a few eosinophils. A small proportion of these entrapped schistosomula showed structural damage. In contrast, schistosomula in the lungs of immune mice were essentially without cellular association. It appears from our work that the adherence of neutrophils to schistosomula in immune mouse skin contributes to a reduction in the number of worms which subsequently develop.