Alternatively activated macrophages induced by nematode infection inhibit proliferation via cell-to-cell contact


  • The first two authors contributed equally to the work.


The cytokine microenvironment is thought to play an important role in the generation of immunoregulatory cells. Nematode infections are commonly associated with Th2 cytokines and hyporesponsive T cells. Here we show that IL-4-dependent macrophages recruited in vivo by the nematode parasite Brugia malayi actively suppress the proliferation of lymphocytes on co-culture in vitro. These alternatively activated macrophages block proliferation by cell-to-cell contact, implicating a receptor-mediated mechanism. Further, the proliferative block is reversible and is not a result of apoptosis. Suppressed cells accumulate in the G1 and G2 / M phase of the cell cycle. Interestingly, the G1 and G2 / M block correlates with increased levels of Ki-67 protein, suggesting a mechanism that affects degradation of cell cycle proteins. We also show that, in addition to lymphocyte cell lines of murine origin, these suppressive cells can inhibit proliferation of a wide range of transformed human carcinoma lines. Our data reveal a novel mechanism of proliferative suppression induced by a parasitic nematode that acts via IL-4-dependent macrophages. These macrophages may function as important immune regulatory cells in both infectious and noninfectious disease contexts.