Resistance to L1210 mouse leukemia cells in moderately protein-malnourished BALB/c mice treated in vivo with thymosin fraction V.

Moderate protein malnutrition retarded the i.p. proliferation of L1210 mouse leukemia cells in BALB/c mice. The increased resistance against leukemia cell growth in protein-malnourished mice was correlated with increased in vitro mitogenic responsiveness of spleen lymphocytes to phytohemagglutinin and increased levels of serum corticosterone but could not be correlated with altered development of splenic lymphocyte-mediated cytotoxicity. The increased resistance against leukemia cells in well-fed mice treated with thymosin alone could not be correlated with an increase in any of these parameters. Treatment with Thymosin Fraction V further increased the resistance of protein-malnourished mice to i.p. leukemia cell growth. The increased resistance of these mice to tumor cell growth was correlated with increased splenic lymphocyte mitogenic responsiveness to phytohemagglutinin, elevated serum corticosterone levels, and a slight increase in lymphocyte-mediated cytotoxicity 14 days after tumor challenge. For 7 days after the last treatment, protein-malnourished mice had reduced serum corticosterone levels. Nevertheless, the serum corticosterone levels were still higher than normal in these mice.