Pattern and Evolution of C4d Staining of Ischemic Myocardial Injury: Implications for the Interpretation of Post-Transplant Endomyocardial Biopsies

C4d immunohistochemical staining is a marker of recent classical pathway complement activation that is useful for evaluation of antibody-mediated rejection in transplant biopsies. C4d also stains areas of myocyte necrosis. We describe the pattern and intensity of myocyte, interstitial, and microvascular staining at different stages of ischemic injury/infarction in the non- transplant setting. Thirty autopsies with ischemic injury were reviewed. Nine acute myocardial infarction, 3 contraction band necrosis, 9 subendocardial ischemic, and 9 chronic ischemic injury/scarring cases were stained with polyclonal antibody for C4d. Results: Acute myocardial infarction and subendocardial ischemic injury cases showed strong staining of necrotic myocytes; larger infarcts showed more intense peripheral versus central staining. Subendocardial ischemic injury was easier to quantify versus HE5(2):64-70.]