8123
This system allowed us to efficiently express in developing thymocytes a mutant form of the NF-kappa B inhibitor I kappa B alpha ( mut-I kappa B ) and to study the maturation defects occurring when NF-kappa B activation is inhibited during fetal development.
 NF-kappa B, NF-kappa B, mut-I kappa B, I kappa B alpha
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:
 NF-kappa B, NF-kappa B, mut-I kappa B, I kappa B alpha