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: RESULTS : We found PTCR in 14 of 15 cases of TG , in 7 transplant biopsy specimens without TG , and in 13 of 143 native kidney biopsy specimens .
### Output Text:
RESULTS : We found PTCR in 14 of 15 cases of TG , in 7 transplant biopsy specimens without TG , and in 13 of 143 native kidney biopsy specimens . 