The effect of Corynebacterium parvum on the proliferation of monocyte precursors in the bone marrow of mice.

The anti-tumour activity of C. parvum is thought to be mediated via the monocyte/macrophage system (Scott, 1974). These cells originate from rapidly dividing precursors in the bone marrow and it might be at this level that C. parvum exerts its action. To test this hypothesis bone marrow T0 Swiss mice has been cultured according to the method of Bradley and Metcalf (1966), which gives an index of the number of proliferating macrophage precursor cells at the time of sacrifice. Experiments were set up at various times following a single i.p. injection of 700 microgram of an anti-tumour strain of C. parvum (CN 6134-Wellcome Research Laboratories). Controls received 700 microgram of either C. diphtheriae CN 2000 or C. parvum CN 5888, a strain with no anti-tumour activity. Macrophage colony counts in those mice receiving "active" C. parvum were significantly higher than those in controls at intervals from 2 h to 3 weeks post-treatment. This time course parallels certain immunological properties of C. parvum and suggests a possible mode of action.