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: This data suggests that E2 modifies the expression of CD36 at the level of protein expression in monocyte - derived macrophages resulting in reduced cholesteryl ester accumulation following ritonavir treatment .
### Output Text:
This data suggests that <span class="chemical">E2</span> modifies the expression of CD36 at the level of protein expression in monocyte - derived macrophages resulting in reduced <span class="chemical">cholesteryl ester</span> accumulation following <span class="chemical">ritonavir</span> treatment . 