Why do viruses that have jumped hosts (such as from bats to humans) cause much more severe infection?

2.) What does “mast cell degranulation that causes speedy histamine and cytokine-driven inflammatory responses” mean in terms of immunology and the human body? How does this kind of inflammatory response occur in autoimmune diseases, and what similar kind of response occurs during Covid-19 infection?
3.) Describe the role of cytokines and interleukins in cell signaling cascades and the immune response? Why does this make the inflammatory response an important part of the immune response?