Influence of anti-inflammatory drugs on the interaction of lymphocytes and macrophages.

The helper function of macrophages in lymphocyte stimulation is well known, but there are indications that macrophages may also exert a suppressor effect on lymphocytes. This effect might be due to prostaglandins secreted by the macrophages. In order to test this hypothesis anti-inflammatory drugs, some of which are known inhibitors of prostaglandin synthesis, were added to a series of phytohaemagglutinin (PHA)-stimulated lymphocyte cultures containing different proportions of macrophages and lymphocytes. The experiments showed that high concentrations of all drugs were inhibitory. Moderate concentrations of some of the PG-synthesis-inhibiting drugs (like indomethacin and mefenamic acid), however, appeared to have a stimulatory effect. The stimulation was more pronounced in cultures containing a high proportion of macrophages. These results support the assumption that macrophages release prostaglandins, which suppress PHA-induced lymphocyte proliferation.