This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Macrophage chemotactic factor is - 
Select and explain. 
A. High molecular weight, B. Chymotrypsin sensitive, C. Heat labile, D. Are antigenically similar to C3
B: Chymotrypsin sensitive
Answer: B: Chymotrypsin sensitive 
Explanation: Ans is 'b' i.e.,Chymotrypsin sensitive (Ref Immunology p. 278)Macrophage chemotactic factor propeies has Low molecular weight (12000), has a isoelectric points of 10.1 & 5.6, and is sensitive to treatment by chymotrypsin while resistant to RNase and neuraminidase.It is heat stable and angenically different from C3 & C5.