![Fig. 3. IFN-γ primes the fas pathway in vitro and in vivo. (A) Results of one representative experiment (of four separate experiments) of BM cells from an FAC −/− mouse (□) and from an FAC −/+ (○) littermate. Cells were exposed to various doses of recombinant murine IFN-γ for 60 minutes, followed by 3-hour exposure to antimurine fas antibodies (“FA-C/fas” [▪] and “hetero/fas” [•]) or medium alone (“FA-C” [□] and “Hetero” [○]). Open and closed circles represent clonal growth of BFU-E from FAC −/+ mice. Open and closed squares represent BFU-E growth of marrow cells from FAC mice. Responses of FAC cells were distinctly abnormal in three ways: (1) BFU-E were suppressed by IFN-γ alone at doses (0.05 and 0.5 ng/mL) that had no suppressive effect on FAC −/+ cells, (2) the addition of anti-fas to FAC cells, even without prior exposure to IFN-γ, resulted in clonal suppression, and (3) the “priming” effect of IFN-γ in FAC-cells (the degree to which the addition of anti-fas augmented fractional BFU-E suppression at every IFN-γ dose) was greater at these low doses of IFN-γ as compared with FAC −/+ progenitor cells. Fas priming occurred in FAC −/+ mice at every dose of IFN, but was most notable at 5.0 ng/mL. At that dose, in two consecutive studies (in cells from each mouse, each variable was quantified using mean colony counts of triplicate plates) exposure of FAC −/− marrow cells to agonistic fas antibody reduced BFU-E to 10.7% control growth while exposure of heterozygote marrow to the antibody reduced BFU-E growth to 52% of control values (P < .005, by Student's t-test). (B) IFN-γ administration in vivo induces fas expression and reduces progenitor cell number in spleen and BM of FAC mice. Two sets of paired mice were treated with 105 U IFN-γ/d intraperitoneally for 5 days. Results were comparable in both experiments (bars reflect means ± SD). BM BFU-E were significantly suppressed in IFN-γ–treated heterozygote mice, but the fractional reduction was significantly greater in BM of FAC −/− mice. Splenic BFU-E increased in treated heterozygotes but were markedly suppressed in FAC −/− mice. (C) Treatment of unfractionated marrow cells from FAC −/+ mice with anti-fas antibody did not suppress BFU-E growth but did suppress BFU-E growth in the FA-C cells by 50%.](https://ash.silverchair-cdn.com/ash/content_public/journal/blood/90/3/10.1182_blood.v90.3.974/4/bl_0072f3a.jpeg?Expires=1735507148&Signature=GIVk9aY4roeGrtH6DTeiWbP533b6TJ6tCZ8bnImorSPPlU4bB9U3B~cDdu6y3-Je~LEBG4MfaoP6JZFFqcikr8tXxucdMZdQfEEdQphpVrLda6-ZrTSqMziLFeIF23GMBFZFT2pBXt8Cw2ggiOtF-6Nu2fq31o473fCMs250775ULV1zSlBJ6gb4d33NpPyWhnh1uNzf8DDVmvFmWPVEf6kVwUJzV~II42eLpxq9NeMNvnuF9CiU03p9Ffr1iyp3WOGtli8voYHjVP57e1y72T0eUJC6fNpUJ8aZsCzNife9AbLMUSzc~8DBXUh7jCWCpRGe19AsDvxYKJMBV-9z8g__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA)
IFN-γ primes the fas pathway in vitro and in vivo. (A) Results of one representative experiment (of four separate experiments) of BM cells from an FAC −/− mouse (□) and from an FAC −/+ (○) littermate. Cells were exposed to various doses of recombinant murine IFN-γ for 60 minutes, followed by 3-hour exposure to antimurine fas antibodies (“FA-C/fas” [▪] and “hetero/fas” [•]) or medium alone (“FA-C” [□] and “Hetero” [○]). Open and closed circles represent clonal growth of BFU-E from FAC −/+ mice. Open and closed squares represent BFU-E growth of marrow cells from FAC mice. Responses of FAC cells were distinctly abnormal in three ways: (1) BFU-E were suppressed by IFN-γ alone at doses (0.05 and 0.5 ng/mL) that had no suppressive effect on FAC −/+ cells, (2) the addition of anti-fas to FAC cells, even without prior exposure to IFN-γ, resulted in clonal suppression, and (3) the “priming” effect of IFN-γ in FAC-cells (the degree to which the addition of anti-fas augmented fractional BFU-E suppression at every IFN-γ dose) was greater at these low doses of IFN-γ as compared with FAC −/+ progenitor cells. Fas priming occurred in FAC −/+ mice at every dose of IFN, but was most notable at 5.0 ng/mL. At that dose, in two consecutive studies (in cells from each mouse, each variable was quantified using mean colony counts of triplicate plates) exposure of FAC −/− marrow cells to agonistic fas antibody reduced BFU-E to 10.7% control growth while exposure of heterozygote marrow to the antibody reduced BFU-E growth to 52% of control values (P < .005, by Student's t-test). (B) IFN-γ administration in vivo induces fas expression and reduces progenitor cell number in spleen and BM of FAC mice. Two sets of paired mice were treated with 105 U IFN-γ/d intraperitoneally for 5 days. Results were comparable in both experiments (bars reflect means ± SD). BM BFU-E were significantly suppressed in IFN-γ–treated heterozygote mice, but the fractional reduction was significantly greater in BM of FAC −/− mice. Splenic BFU-E increased in treated heterozygotes but were markedly suppressed in FAC −/− mice. (C) Treatment of unfractionated marrow cells from FAC −/+ mice with anti-fas antibody did not suppress BFU-E growth but did suppress BFU-E growth in the FA-C cells by 50%.
