Macrophages and methylthio groups in lymphocyte proliferation

Macrophages are shown to replace methylthio disulfides in supporting in vitro proliferation of three cell lines previously characterized as methylthio-dependent. Macrophages have the capacity to generate methylthio groups from methylthioadenosine. It is hypothesized that macrophages stimulate cell proliferation both in normal immune systems and in certain cancers by providing an abundance of methylthio groups. Fetal calf serum is shown to contain methylthio groups. It appears that, in cell cultures containing fetal calf serum, sulfhydryl compounds stimulate cell proliferation by making the methylthio groups in the serum available to the cells.