components of the immune system that everyone is born with.
Pre-existing and non-specific defense immunity with a very low memory component if any. As the primitive immune response against bacteria, it is present in invertebrates and vertebrates.
In an evolutionary sense, this is the ancestral immunity present in normal individuals at all times and does not increase with repeated exposure to a given pathogen. Responsible for clearance of most infections (Lecture: Acquired Immunity, 2/14/02)