B lymphopoiesis is modulated by TC-PTP. In the absence of TC-PTP, bone marrow stromal cells provide an abnormal cytokine environment. IFN-γ secretion by bone marrow stromal cells induces Stat1 phosphorylation of pre-B cells leading to decreased number of pre-B cells expressing surface IL-7R thus reducing IL-7 proliferation response. IFN-γ also induces apoptosis in those pre-B cells leading to a decreased immature IgM⁺ B-cell population.