Immature B cells are susceptible to apoptosis due to ligation of surface immunoglobulin receptors. The WEHI 231 cell line represents a useful model to study the mode of action of factors preventing apoptosis. In this work we investigated the protective effects of multi-species lactoferrins in anti-mouse Ig-induced WEHI 231 cell death. Bovine milk-derived lactoferrin (bLF), recombinant human lactoferrin expressed in Chinese hamster ovary cells – rhLF(CHO) or in human endothelial kidney cells – rhLF(HEK), and recombinant mouse lactoferrin expressed in Chinese hamster ovary cells – rmLF(CHO), were used. Goat-anti-mouse Ig antibodies were used to induce cell apoptosis. Survival of WEHI 231 cells in culture was measured using the colorimetric MTT method. Expression of signalling molecules and sub-units of interleukin 2 receptor was determined by the RT PCR method. The results showed that anti-mouse Ig antibodies inhibited cell growth in a dose-dependent manner. The lactoferrins alone had no effect on the cell survival. The cells exposed to LFs, prior to anti-Ig treatment, were rescued to a significant degree from cell death. Determination of the signalling molecule expression revealed almost complete suppression of caspase-3 and NF-κB1 by bLF in untreated cells, as well as deep suppression of caspase-3, block of Fas, and 4-fold increase of NF-κB1 in cells incubated with bLF prior to anti-Ig treatment. In addition, differential changes in the expression of inter-leukin 2 subunits upon bLF treatment were found, indicating a process of cell differentiation. In conclusion, we showed that LF-induced cell differentiation in immature B-cell line WEHI 231 was correlated with partial protection of the cells from anti-Ig-induced cell death. and Corresponding author: Michał Zimecki