Fig. 5. Effect of T3 on the differentiation of spleen and bone marrow erythroblast primary cultures. After 7 days in culture, in proliferation conditions, erythroblasts derived from either spleen or bone marrow were switched to medium that favors their differentiation in the presence or absence of 10^-7 mol T3. (A,C) Growth curves of respectively spleen- and bone-marrow-derived erythroblasts. Cell numbers during differentiation were determined at the indicated timepoint by Trypan Blue exclusion. (B) Spleen culture and (D) bone marrow culture show the morphology of differentiating cells after staining with MGG and neutral benzidine together with the corresponding cumulative numbers of hemoglobin-positive (red bars) and hemoglobin-negative (white bars) cells in the presence or absence of T3 (^*P<0.05; ^**P<0.01; n=3 for each condition). The numerous small brownish bodies in B at 42 hours in the presence of T3 represent orthochromatophilic erythroblasts with a thin rim of cytoplasm and a highly condensed nucleus and expelled nuclei. These orthochromatophilic erythroblasts were scored as hemoglobin-positive cells. (E,F) Cumulative numbers of differentiating cells and hemoglobin-positive and hemoglobin-negative cells in cultures of TR^0/0 spleen (E) and bone marrow (F) cultures. (No statistical differences were observed in hemoglobin-positive cell numbers between -T3 and +T3 at the respective times; n=3 for each condition).