In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: METHODS : The expression of MRP2 and Pgp in brain and liver sections of TR ( - ) rats and normal Wistar rats was determined with immunohistochemistry , by using a novel , highly selective monoclonal MRP2 antibody and the monoclonal Pgp antibody C219 , respectively .
### Output Text:
METHODS : The expression of MRP2 and Pgp in brain and liver sections of TR ( - ) rats and normal Wistar rats was determined with immunohistochemistry , by using a novel , highly selective monoclonal MRP2 antibody and the monoclonal Pgp antibody C219 , respectively . 