Elevated levels of lead have been found in waterfowl, due to human activities. Lead may cause immunomodulatory effects, but the mechanisms are largely unknown, especially after viral challenges. To characterize avian immunomodulatory hazards of lead (Pb)2+, we used chicken macrophage (HD‐11) and B‐lymphocyte (DT40) cell lines, as in vitro models for the innate and adaptive immune systems, respectively. The cells were activated via toll‐like receptor‐3 by polyinosinic–polycytidylic acid sodium salt (poly I:C), mimicking viral infections. Our results indicate that Pb2+ is cytotoxic to both cell lines, macrophages being more sensitive. De novo synthesis of glutathione plays an important role in protecting macrophages from Pb2+ intoxication, which might also be closely involved in the induction of nitric oxide after Pb2+ exposure. Stimulatory effects on cell proliferation were noticed at noncytotoxic Pb2+ concentrations as well. Exposure to Pb2+ could also affect the inflammatory status by inhibiting the pro‐inflammatory interferon (IFN)‐γ while promoting the production of anti‐inflammatory type I IFNs in both macrophages and B‐cells, and increasing intracellular IgM levels in B‐cells. These results suggest that the immunomodulatory effects of Pb2+ in birds are probably closely associated with disruption of immune cell proliferation and cytokine production, potentially causing disorders of the avian immune system. Environ Toxicol Chem 2020;39:1060–1070. © 2020 SETAC