Which of the Following Statements About the Immune System Is

Which of the following statements about the immune system is correct?

A) Memory cells are involved in a primary immune response.
B) Dendritic cells were first identified in the nervous system.
C) Interferons are specific proteins that block cell replication at the level of mitosis.
D) Natural killer cells are involved in both specific and nonspecific immune responses.
E) Defensins are one type of protective protein synthesized by T helper cells.