Table 1.

Components of the IGF axis and relevant features.

Insulin Growth Factor 1 (IGF1)	Binds IGF1R and hybrid receptors
Insulin Growth Factor 2 (IGF2)	Binds IGF1R, IGF2R, IR-A and hybrid receptors
Insulin	Binds IR-A, IR-B and IGF1R
Insulin Growth Factor Receptor 1 (IGF1R)	Binds IGF1 and IGF2 with high affinity, and insulin with low affinity
Insulin Growth Factor 2/Mannose-6-phosphate Receptor (IGF2/M6P-R or IGF2R)	Binds IGF2 Lacks intracellular signaling
Insulin Receptor A (IR-A)	Lacks exon 11 (splice variant) Binds insulin and IGF2 with high affinity
Insulin Receptor B (IR-B)	Contains exon 11 (splice variant) Binds insulin with high affinity
IGF1R/IR-A	Hybrid Receptor
IGF1R/IR-B	Hybrid Receptor
IGF binding protein 1–6 (IGFBP1-6)	Bind IGF1 and IGF2, forming tertiary complexes with IGFALS and prolonging growth factors half-life.
IGF binding protein 7–8 (IGFBP7-8)	Bind IGF1 with low affinity
Acid-labile subunit (IGFALS)	85 KD protein, member of leucin-rich repeats superfamily. Prolongs half-life of IGFBP3/5 and IGF1 binary complexes.