Suppressor macrophages in tumor-bearing mice. Inconsistency between in vivo and in vitro findings?

The growth of a spontaneous adenocarcinoma (ADK-1t) of BALB/c mice (H-2d, MIsb) induces progressive hyporesponsiveness of spleen cells stimulated with PHA or irradiated leukocytes from DBA/2 strain (H-2d, MIsa) in mixed leukocyte culture. This hyporesponsiveness is due to the suppressor activity of macrophage-like cells, since it is abrogated by passage over nylon-wool columns, pretreatment with carrageenans, or carbonyl iron and magnet. BALB/c mice bearing greater than 20 mm mean diameter ADK-1t tumors, and displaying a drastic impairment of T lymphocyte reactivity in vitro, were challenged with the P815 mastocytoma of the DBA/2 strain. These mice rejected increasing numbers of P815 cells to the same extent as normal BALB/c mice. The reactivity towards P815 is abrogated by 450 rad, and can be reconstituted by the adoptive transfer of 2 X 10(7) normal T lymphocytes in either normal or ADK-1t bearing BALB/c mice. These data show that a discrepancy exists between the capacity of T lymphocytes from ADK-1t bearing mice to react against DBA/2 cells tested in vitro or in vivo, and indicates that great caution should be exercised in predicting the responsiveness of the immune system on the basis of in vitro data on the suppressor activity of macrophages.