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: We found an increase of IL - 6 for only three patients , but only one patient reported myalgia ; no relationship between myalgia and the increase of IL - 6 was found .
### Output Text:
We found an increase of IL - 6 for only three patients , but only one patient reported myalgia ; no relationship between myalgia and the increase of IL - 6 was found . 