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Activation of T cells is initiated by the recognition of antigen on antigen presenting cells to exert the effector functions in immune and inflammatory responses .
 cell type: T cells; cell type: antigen presenting cells; protein: antigen
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
 Entities: T cells, antigen presenting cells, antigen 
Answer:
 cell type: T cells; cell type: antigen presenting cells; protein: antigen