Induction of T cell-independent eosinophilia in mice with polymyxin B and schistosome infection.

This study examined the elevation of blood eosinophil counts in athymic and thymus-intact mice after repeated injections of polymyxin B with and without infection by Schistosoma mansoni. In athymic mice, a modest, comparable eosinophilia occurred after polymyxin B injection or parasite infection alone, or after a combination of both. In thymus-intact mice, polymyxin B injection caused a similar low grade eosinophilia, and schistosome infection produced a much higher level of eosinophilia. The combination resulted in the highest levels during the early weeks after infection; this hyperresponsive phenomenon was most apparent following 5 to 7 weekly polymyxin B injections, and the total eosinophil count approximated that derived by adding the eosinophil counts induced by polymyxin B injections or schistosome infection alone. In spite of the changes in blood eosinophil counts, tissue eosinophilia in the liver revealed no apparent differences. Furthermore, in schistosome-infected and polymyxin B-injected thymus-intact mice, hepatic granulomas reached a maximal size earlier than in mice that were only infected, and there was an over-all reduction in mast cell counts. The findings indicate that a T cell-independent eosinophilia occurs under a variety of circumstances. In athymic mice, it accounts for all peripheral eosinophilia, whereas in thymus-intact mice, it operates independently from the well known T cell-dependent eosinophilia of parasite infections.