This is the function of the innate immune system
which defends us against any foreign agent regardless of type of species.
Key components include:
- skin and mucous membrane (mouth, nose etc) which act as physical barriers preventing access of microbes to underlying tissues.
- A variety of cells (such as leucocytes and natural killer cells) which circulate in the blood stream and engulf and eliminate microbes, pollen or dust etc that succeed in entering the body.
- Plasma proteins that circulate in the bloodstream or lymphatic system.