Quantitative immunohistochemistry of PDGFRα, PDGFRβ, c-KIT and CSF1R in human PAH lung samples

Abstract

<b>Introduction:</b> We assessed potential therapeutic target relevance of PDGFR, CSF1R, and c-KIT in human control and idiopathic pulmonary arterial hypertension (IPAH) lungs by quantitative immunohistochemistry (IHC). <b>Methods:</b> Lung samples were obtained from the Pulmonary Hypertension Breakthrough Initiative (10 IPAH, 10 controls). Paraffin embedded sections were stained with antibodies against PDGFRα, PDGFRβ, CD117 (KIT) and CSF1R. Masked analysis of IHC samples was performed with MetaMorph^®. Correlation analysis was performed for integrated intensity vs. pulmonary arterial area. <b>Results:</b> Integrated intensity signals, representing the sum of positive pixels, for PDGFRα, PDGFRβ, CSF1R, and c-KIT were significantly increased in PAH samples vs. controls. PDGFRα and PDGFRβ were increased in IPAH obliterative lesions and perivascular tissue. c-KIT was expressed in perivascular inflammatory regions. CSF1R expression was noted in the intima of control pulmonary arteries and alveolar macrophages; in IPAH lungs, there was marked expression in intima of obliterative lesions, with expression in macrophages. There was a high correlation (R2&gt;0.9, p&lt;0.0001 for all targets) between integrated intensity and positive area, indicating that increased integrated intensity was likely due to an increase in cell area expressing the targets rather than an increased signal density per cell. <b>Conclusions:</b> Quantitative IHC of human PAH lung samples demonstrated a significant increase in PDGFRα, PDGFRβ, c-KIT and CSF1R vs. controls. This is the first report of increased CSF1R expression in human PAH lesions and supports targeting CSF1R as a treatment strategy for PAH in addition to PDGFR and KIT.