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: Antibodies against the astroglia - specific cytoskeletal protein , glial fibrillary acidic protein ( GFAP ) , and against the glial calcium - binding protein , S - 100 protein , were used to assess the status of astrocytes .
### Output Text:
Antibodies against the astroglia - specific cytoskeletal protein , glial fibrillary acidic protein ( GFAP ) , and against the glial <span class="chemical">calcium</span> - binding protein , S - 100 protein , were used to assess the status of astrocytes . 