TNF and Bloom syndrome: Because BLM treatment was able to increase TNF levels in mouse serum (data not shown) and CY, an agent known to eliminate TNFR2-expressing Tregs15, was able to abrogate this expansion of Tregs in BLM-treated mice, we hypothesized that the enhanced interaction of TNF-TNFR2 was responsible for the expansion of Tregs by in vivo BLM treatment.