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It has long been a puzzle that MHC class II molecules are expressed in human T cells after activation but not in mouse T cells ; this expression is believed to play a role in the cell mediated immune response .
 protein: MHC class II molecules; cell type: human T cells; cell type: mouse T cells
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 protein: MHC class II molecules; cell type: human T cells; cell type: mouse T cells