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: E2 decreased the accumulation of cholesteryl esters in macrophages following ritonavir treatment .
### Output Text:
<span class="chemical">E2</span> decreased the accumulation of <span class="chemical">cholesteryl esters</span> in macrophages following <span class="chemical">ritonavir</span> treatment . 