Bovine (BLF) and human (HLF) lactoferrin inhibit proliferation and cytokine production by an antigen specific TH1 cell line stimulated with antigen presenting cells (APC) and antigen. Beside the inhibitory effects on TH1 cells we observed a decrease of interleukin 2 receptor (IL-2R) expression on these cells contacted with LF. Lactoferrin (LF) did not inhibit proliferation of indicator HT-2 cells to IL-2 suggesting lack of interference with IL-2/IL-2R interaction by LF. No inhibitory effect was observed on proliferation and cytokine production by TH2 cell lines and no changes in interleukin 4 receptor (IL-4R) levels were found with regard to TH2 cell line. We conclude that LF has differential activity with regard to effector functions of antigen-specific T cells by inhibiting TH1 but not TH2-mediated immune responses.