Award Date


Degree Type


Degree Name

Master of Science (MS)



First Committee Member

Bryan L. Spangelo

Number of Pages



Thymosin fraction 5 (TF5), comprised of an array of small molecular weight peptides, partially purified from the adult bovine thymus gland, contains multiple biologically active humoral factors. TF5 influences T cell differentiation, lymphokine production and restores immune deficiencies in a variety of animal models in vitro and in vivo. Because TF5 generally enhances immune reactivity, we examined the effects of TF5 on the proliferation of HL-60 human promyelocytic leukemia cells. Direct viable dye cell counting, the MTT reaction, and the clonogenic potential of HL-60 cells were used to determine cell proliferation. The potency and efficacy of TF5 for the inhibition HL-60 cell proliferation was similar in all three measures of proliferation. In contrast to HL-60 cells, TF5 only induced a modest suppression of human melanoma CRL7686 cell proliferation. Known apoptosis inhibitors did not reverse the effect of TF5 on HL-60 cell proliferation indicating that TF5 acts through a non-apoptotic mechanism. The results of morphological analyses and the TUNEL assay demonstrate that TF5 does not induce apoptosis in HL-60 cells, suggesting that the mechanism of inhibition involves cytostasis. Further purification of TF5 by gel filtration chromatography produces a biologically active factor of approximately 20 kDa. Since the parent compound is composed of peptides less than 15 kDa, these results suggest the possible formation of oligomers. Electrophoresis of the active factor on polyacrylamide gels indicates that it contains at least four components in the 5--15 kDa molecular weight range; These results demonstrate that an activity in TF5 exerts an anti-proliferative effect in human myeloid leukemia cells through a cytostatic mechanism; these studies suggest that a thymic hormone immune surveillance mechanism may limit the onset of certain types of leukemia.


Cells; Effects; Hormone; Human; Leukemia; Myelogenous; Proliferation; Thymic

Controlled Subject

Biochemistry; Cellular biology; Oncology

File Format


File Size

2283.52 KB

Degree Grantor

University of Nevada, Las Vegas




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