Cellular reactions in guinea-pigs following primary and challenge infection with Trichostrongylus colubriformis with special reference to the roles played by eosinophils and basophils in rejection of the parasite.

The cellular changes which occur in blood, bone marrow, and small intestines of guinea-pigs during a primary infection and after a challenge infection with are described. These studies show that (1) the dominant haematological and histological changes which follow infection with the parasites are proliferation of eosinophil and basophil leucocytes in the bone marrow, a circulating eosinophilia and basophilia, and an accumulation and degranulation of these cells at the site of infection. (2) The eosinophil and basophil changes occur at an accelerated rate in animals reinfected with . These reach their peak 5–7 days after reinfection compared with 21–28 days in previously uninfected animals, and these peaks are correlated with the time of rejection of the parasite. In a previous study (Rothwell, Dineen and Love, 1971) it was shown that histamine and/or 5-hydroxytryptamine participate in the rejection of in the guinea-pig. As the results of the present study show that the accumulation and degranulation of eosinophils and basophils at the site of infection is correlated with rejection of the parasite, it is concluded that these cells are the source of the pharmacologically active amines.