Previous studies have shown that the cell surface expression of thymus leukemia antigen (TL) on ASL-1w leukemia cells varies with the progression of the cells through the growth cycle. Expression of TL is maximal in S phase, and its quantitative expression varies directly with DNA synthesis. In the present study, the effect of anti-TL serum on the growth of ASL-1w cells was examined. The antiserum, tested in the absence of complement, affected the growth of these cells in biphasic manner. When the antiserum concentration was 0.1% or greater, there was a rapid decline in the rate of DNA synthesis, and after 5 to 7 hr, cell death. When the antiserum concentration was 0.067% or less, the decline in the rate of synthesis of DNA did not become apparent until 5 to 6 hr after treatment. Under these conditions, there was approximately a 20% increase in cell number after 24 hr of culture. The hypothesis that treatment of ASL-1w cells with the lesser concentration of anti-TL serum blocks the cells in G2 phase of the cell cycle is discussed.

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This work was supported by the American Cancer Society Grant IM 111 and by the National Institutes of Health Grant NCI CA-24914.

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