12246
BACKGROUND: Inhibition of complement in small animal models of xenotransplantation has demonstrated graft infiltration with natural killer (NK) cells and monocytes associated with endothelial cell ( EC ) activation .
 natural killer (NK) cells, endothelial cell, EC
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 natural killer (NK) cells, endothelial cell, EC