NNT-1/BCSF-3 is a neurotrophic factor with B-cell-stimulating capabilities. Expressed in the lymph nodes and spleen, NNT-1/BCSF-3 activates glycoprotein 130 (gp130) and leukemia inhibitory factor receptor member b (LIFR-b) by binding and inducing the 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 increases in serum IgG and IgM. Recombinant Human NNT-1/BCSF-3 is a 22.4 kDa protein containing 199 amino acid residues.