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: B2 receptor - deficient mice were less sensitive to this drug than the WT mice , as shown by reduced weight loss , better preservation of kidney function , down regulation of inflammatory cytokines and less acute tubular necrosis .
### Output Text:
B2 receptor - deficient mice were less sensitive to this drug than the WT mice , as shown by reduced weight loss , better preservation of kidney function , down regulation of inflammatory cytokines and less acute tubular necrosis . 