603
Both in vitro - synthesized S2 protein and synthetic peptides corresponding to S2 are shown to react positively with sera obtained from EIAV - infected horses , providing the first direct evidence of expression of this protein in infected animals .
 S2 protein, S2
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 S2 protein, S2