As Shark Week rolls on, Discovery News continues its mini-series of questions about sharks, asking the experts about the things that make us curious. Here, we ask Dr. Lauren Smith about the shark immune system and why it's fascinating.

Lauren holds a doctorate in marine biology and specializes in shark research. Among her goals is to dispel the myths and rumors derived from a fundamental misunderstanding of sharks. She's a member of the Gills Club, an all-women group of scientists dedicated to both shark science and to fostering young girls' interest in them. She also runs the website Saltwater Life, which blends scientific research, a blog and galleries, and an overall appreciation for ocean conservation, enjoyment and appreciation. Follow her on Twitter @SaltwaterlifeUK.

Here is Lauren's answer:

"Sharks possess two types of immunity. The first is called "natural," or innate immunity. This provides the first type of defense against invading pathogens (things that cause diseases, such as bacteria or viruses). The cells used in natural immunity respond in a generic way, and all animal and plant life possess this type of immunity.

"What is special about sharks, and indeed all cartilaginous fish, is that they are, in terms of evolution, the oldest group relative to mammals that also has a second type of immunity known as "adaptive." With adaptive immunity, an immunological memory is generated following an initial exposure to an infectious pathogen. If that pathogen is encountered again, the immune system is able to recognize it and attack it much faster and more effectively. This type of immunity is the basis of vaccination!"

Tune in to Shark Week all this week at 9/8 central on Discovery Channel.