Polyplax serrata (Phthiraptera: Hoplopleuridae): effects of cortisone and cyclophosphamide on the acquired resistance response of mice to lice

One 4-mg injection of long-acting cortisone per mouse, after acquired resistance to lice had developed, suppressed most of the inflammatory cells in the skin over a period of 10–12 days and louse numbers increased over a 2-wk period. The mode of action of the cortisone was considered to be anti-inflammatory rather than immunosuppressant, and no clue as to the nature of host resistance could be discovered. However, 4 mg cyclophosphamide (Cy), injected 24 h after infesting the mice, caused prolonged high numbers of lice for 8 weeks, delayed the appearance in the skin of lymphocytes slightly and of fibroblasts for an extended period, but caused no diminution of inflammation. The results of this study suggest that Cy suppressed T-lymphocyte proliferation at the antigen recognition stage early in the infestation and that, at least initially, a cell-mediated mechanism appeared to be a prerequisite for expression of resistance.