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Activation of nonreceptor protein tyrosine kinases ( PTKs ) is essential for T cell receptor ( TCR ) responsiveness ; however, the function of individual PTK substrates is often uncertain.
 nonreceptor protein tyrosine kinases, PTKs, T cell receptor, tyrosine kinases, PTK substrates, TCR
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:
 nonreceptor protein tyrosine kinases, PTKs, T cell receptor, tyrosine kinases, PTK substrates, TCR