Secretion of IFN-γ by TC-PTP^−/− bone marrow stromal cells. (A) Semiquantitative RT-PCR analysis of IFN-γ expression. cDNA was prepared from purified bone marrow stromal cells and pre-B cells and from total spleen. The presence of IFN-γ and β-actin transcripts was assayed by PCR in the same reaction. (B) Bone marrow stromal cell cultures (passage 5) from TC-PTP^+/+ and TC-PTP^−/− mice at P7 were stained for surface expression of markers shown in Figure S1 and intracellular expression of IFN-γ for flow cytometry analysis. Nonspecific IgG was used as negative control for intracellular staining. RCN is plotted against IgG (thin line) or IFN-γ (thick line) fluorescence. MFI is indicated. (C) Quantitation of IFN-γ secretion by ELISA. Primary bone marrow stromal cell cultures were established. After 5 or 6 passages, the culture medium was replaced and the concentration of IFN-γ was measured by ELISA 24 hours later. Data from 10 TC-PTP^+/+ (○) and 9 TC-PTP^−/− (•) stromal cell cultures are represented. The difference between the 2 groups was significant (P < .02). All experiments were repeated at least 3 times.