Tumor-associated macrophages of mouse mammary tumors. II. Differential distribution of macrophages from metastatic and nonmetastatic tumors.

Abstract

Macrophage subpopulations were isolated by counterflow centrifugal elutriation from a number of closely related mammary tumors originally derived from a single spontaneous tumor in a BALB/cfC3H mouse. Each tumor line had its own distinct characteristics with regard to tumor cell distribution, macrophage size (density), macrophage content, and macrophage distribution. Although there is no correlation with the metastatic potential of the tumors for the first three characteristics listed, distinct differences are apparent between metastatic and nonmetastatic tumors in macrophage distribution into the elutriated fractions. The distribution of the tumor-associated macrophages was shifted toward the later fractions in the metastatic tumors (lines 66 and 410.4), with approximately 40% more macrophages in fractions 3 and 4 than in those fractions from the nonmetastatic tumors (lines 67 and 168). The levels of three ectoenzymes, leucine aminopeptidase (LAP), alkaline phosphodiesterase I (APD), and 5' nucleotidase (5'N) were determined for macrophages from the elutriated fractions as well as for the total tumor digest. No significant differences were observed in absolute levels of either LAP or APD between most of the fractions from the different tumor lines. Differences were seen between the fractions in levels of 5'N among the lines and in ADP levels between lines 66 and 168 from the total tumor digest. Striking differences in ectoenzyme levels were apparent when the activity was normalized to macrophage surface area: macrophages from line 66 tumors were 3- to 17-fold higher in their LAP concentrations than were macrophages from either 67 or 168 tumors. Each tumor line had a unique and reproducible pattern of macrophage-associated prostaglandin E (PGE) synthesis. The three nonmetastatic tumor lines showed peak PGE levels in fraction three with lower levels in fraction 2, whereas the highly metastatic tumor yielded more active macrophages in fraction 2 vs fraction 3. Changes in PGE levels were associated with differing ectoenzyme levels. Macrophages in fraction 3 from metastatic tumors were enriched for populations with high LAP activity and low PGE levels. Conversely, macrophages from nonmetastatic tumors exhibited lower LAP activity in fraction 3 vs 2 and increasing PGE levels. Thus, differences between metastatic and nonmetastatic mammary tumors were seen in 1) distribution of macrophages in the elutriation fractions, 2) size of infiltrating macrophages, 3) macrophage ectoenzyme concentrations, and 4) macrophage-associated PGE levels.