IGF1R,also named as CD221,belongs to the protein kinase superfamily,Tyr protein kinase family and Insulin receptor subfamily. IGF1R binds insulin-like growth factor 1 (IGF1) with a high affinity and IGF2 with a lower affinity. It has a tyrosine-protein kinase activity,which is necessary for the activation of the IGF1-stimulated downstream signaling cascade. When present in a hybrid receptor with INSR,IGF1R binds IGF1. The hybrid receptors composed of IGF1R and INSR isoform Long are activated with a high affinity by IGF1,with low affinity by IGF2 and not significantly activated by insulin,and that hybrid receptors composed of IGF1R and INSR isoform Short are activated by IGF1,IGF2 and insulin. In contrast,the hybrid receptors composed of IGF1R and INSR isoform Long and hybrid receptors composed of IGF1R and INSR isoform Short have similar binding characteristics,both bind IGF1 and have a low affinity for insulin. Defects in IGF1R may be a cause in some cases of resistance to insulin-like growth factor 1 (IGF1 resistance). This antibody raised against a synthesized polypeptide (CGVLVLRASFDERQPYAH) corresponding to 1332-1348aa of human IGF1R protein recognizes beta chain of IGF1R.