Instructions: In this task, you are given a sentence. You are expected to write the name of the organism substances in the body mentioned in the input. Although there might be several correct answers, you need to write one of them.
Input:  The adjuvant effect of PSP on OVA - specific IgE and IgG2a responses in different strains of mice Levels of serum OVA - specific IgE ( A ) and IgG2a ( B ) on day 26 after injection into one hind footpad of HBSS ( open columns ) , 10 mug OVA ( gray ) , 40 mug PSP ( hatched ) or 10 mug OVA + 40 mug PSP ( black ) in different mouse strains .
Output:
serum