STAT5B and lymphoma: These results suggest that phosphorylation, or at least strong phosphorylation, may not be necessary for Stat5b to promote lymphocyte proliferation while the progressively increasing phosphorylation of STAT5 observed in NOD.Stat5bTg mice but not in F1 or B6 Stat5b transgenic mice may account for the differences in lymphoma incidences observed in these models.