Background: It is well known that cyclophosphamide (Cy) treatment before sensitization paradoxically enhances rather than suppresses contact hypersensitivity (CH) reactions. In fact, Cy-treated mice developed a significant (p < 0.05) increase of the CH reactions to 2,4,6-trinitro-1-chrolobenzene (TNCB) in comparison with untreated mice.
Objective: In order to examine whether the target cells of Cy in the immuno-augmentative effect are CD25(+) CD4(+) regulatory T cells or not, we investigated effect of Cy treatment on CD25(+) CD4(+) T cells.
Method: We examined Cy-treated CD25(+) CD4(+) T cells by flow cytometer and by inhibition assay on proliferation of CD25(-) CD4(+) T cells.
Results: Cy treatment remarkably reduced the number and percentage of CD25(+) CD4(+) T cells in the spleen and lymph nodes 3 and 5 days later. Moreover, CD25(+) CD4(+) T cells taken from the Cy-treated mice 3 days later showed the lower suppressive activity on proliferation of CD25(-) CD4(+) T cells, as compared to that from the untreated mice. Furthermore, transfer of CD25(+) CD4(+) T cells from untreated mice resulted in a significant decrease (p < 0.05) of the CH reactions enhanced by Cy treatment.
Conclusion: These results indicate that enhancement of the CH reactions to TNCB by Cy treatment is attributed to the decrease in the number, percentage and the function of CD25(+) CD4(+) regulatory T cells.