How many types of barriers make up innate immunity?

1. Innate immunity blocks entry rather than targeting a specific pathogen. 2. It consists of four types of barriers. 3. These are the physical, physiological, cellular and cytokine barriers. 4. Skin is the main physical barrier, along with the mucus coating of the epithelium. _Source: syllabus Biology Ch7 'Human Health and Disease', section 7.2.1_