Larry is taking a walk in the park. the pollen in the air makes him sneeze constantly. what line of defense is his immune system exhibiting?

Larry's immune system would be exhibiting the first line of defense.

The first line of defense includes chemical and physical barriers that prevent various foreign agents from entering the body; such as bacteria. Here, the first line of defense includes the naval cavity. Due to this, Larry is sneezing to bring the pollen back into the environment from his body as a defense action.