Increased infiltration by monocytes in delayed type hypersensitivity site following cyclophosphamide treatment.

Sensitized lymphocytes transferred locally with antigens into footpads of unprinted mice can elicit a delayed-type-hypersensitivity (DTH) reaction. Treatment of recipients with cyclophosphamide (CY) increased the infiltration observed at the DTH site. The enlargement of footpads was detected with low doses of DTH mediating cells as with large ones. An enumeration of circulating monocytes performed on the test days and the preceding days has shown a three to ten fold increase of number of monocytes. During the recovery following CY treatment (20 mg/kg and 200 mg/kg) a rebound effect at level of precursors of monocytes was observed. Thus a dual mechanism is proposed to explain the effect of CY on DTH reaction: a liberation of DTH cells by inhibition of B response as previously described; an increased number of monocytes which can be recruited by DTH-cells in site of antigen injection.