Prostaglandin E2-mediated Inactivation of Various Killer Lineage Cells by Tumor-bearing Host Macrophages

We have previously reported that natural killer (NK) lineage cells are progressively inactivated during tumor development by prostaglandin E2 (PGE2) secreted by host macrophages; that this facilitates spontaneous tumor metastases, which can be prevented by chronic indomethacin therapy (CIT); and that CIT combined with multiple rounds of interleukin 2 (IL-2) can cure experimental metastases and activate all killer lineage cells in situ including NK cells, lymphokine-activated killer (LAK) cells, and tumoricidal macrophages. The present study tested whether PGE2 secreted by tumor-bearing host macrophages exerts pansuppressor effects against the activation of T cells, NK cells, LAK cells, and tumoricidal macrophages from normal splenic cell populations. Macrophages isolated from CBA mice bearing 21-day intraperitoneal Ehrlich ascites tumors (EAT) or C3H/HeJ mice bearing 21-day subcutaneous T58 mammary adenocarcinomas were added (+/- 10(-5) M indomethacin, or a monoclonal anti-PGE2 ab) to syngeneic splenic lymphocytes to examine the effects on 1) polyclonal activation (3-d 3H-thymidine [3H-TdR] uptake) with concanavalin A (Con A); 2) one-way (CBA alpha BALB/C or C3H alpha BALBC) MLR (5-d 3H-TdR uptake) and subsequent CTL generation (tested against 51Cr-labeled Con A blasts of the stimulator phenotype); 3) NK activity (after 24-h co-culture) against YAC-1 targets; 4) generation of LAK cell activity (in the presence of 200 or 2,000 units recombinant IL-2 for 3 or 5 days), tested against NK-sensitive and NK-resistant targets. Similar effects were also noted on the generation of tumoricidal activity in normal splenic macrophages cultured for 3 days in the presence of LPS. Normal splenic macrophages added under the same conditions served as controls. Effects of pure PGE2 or PGF2 alpha (10(-6) M) were also examined on these activation events. Results revealed that tumor-host-derived macrophages (but not normal macrophages) markedly suppressed all these activation events and this suppression was abrogated nearly totally by indomethacin and totally by anti-PGE2 ab, indicating its mediation by PGE2. This finding ran parallel with high levels of PGE2 production by tumor-host-derived but not normal splenic macrophages. Pure PGE2 but not PGF2 alpha mimicked these suppressor effects. While tumoricidal activity was generated in normal macrophages in the presence of LPS, IL-2, or IFN-gamma or their various combinations (which led to further augmentation), these agents required the presence of indomethacin to generate significant killer activity in tumor-host-derived macrophages. macrophages.(ABSTRACT TRUNCATED AT 400 WORDS)