This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Pathology
The following interleukin is characteristically produced in a TH1 response? 
Select and explain. 
A. IL-2, B. IL-4, C. IL-5, D. IL-10
A: IL-2
Answer: A: IL-2 
Explanation: After coming in contact with antigen presenting cells, CD4+ helper T cells secrete IL-2 and expresses high-affinity receptors for IL-2. IL-2 is a growth factor that acts on these T lymphocytes and stimulates their proliferation, leading to an increase in the number of antigen-specific lymphocytes.