NNT-1/BCSF-3 is a neurotrophic factor with B-cell stimulating capabilities. Expressed in lymph nodes and spleen, NNT-1/BCSF-3 binds and activates glycoprotein 130 (gp130) and leukemia inhibitory factor receptor member β (LIFR-β) and induces tyrosine phosphorylation of these receptors. In vitro, it supports the survival of chick embryo motor and sympathetic neurons. In mice, NNT-1/BCSF-3 induces serum amyloid A, causes body weight loss and B cell hyperplasia associated with increased in serum IgG and IgM. Recombinant human NNT-1/BCSF-3 is a 22.4 kDa protein containing 199 amino acid residues.