The innate immune system is the first line of defense against pathogenic microbes. 

The principal components of the innate immune system include: 

1. Anatomical Barriers - The anatomical barriers of the innate immune system encompass various physical, chemical, and biological barriers that act as the first line of defense against pathogens. 

• Physical barriers of the innate immune system include the skin, hair, and mucous membranes in the respiratory, gastrointestinal, and urinary tracts. They work by physically blocking the entry of pathogens into the body. 
• Chemical barriers of the innate immune system include breastmilk, saliva, tears, sweat, mucus, vaginal secretions, and semen. They block the entry of pathogens through openings in the body and inner body surfaces. 
• Biological barriers of the innate immune system are made up of the various harmless bacteria that reside within the gastrointestinal, reproductive, and urinary tracts. These harmless bacteria create an environment that’s inhospitable for harmful bacteria or pathogens to survive within the body. 

2. Cellular Response - Different types of leukocytes that circulate in the blood form the cellular response component of the innate immune system. Leukocytes are capable of single-handedly killing invading pathogens by phagocytosis. This is a cellular process in which the leukocyte extends its plasma membrane and engulfs the harmful pathogen, eventually killing it. The cells involved in phagocytosis include macrophages, neutrophils, and dendritic cells.

3. Blood Proteins - Blood proteins, including members ofthe complement system and other mediators of inflammation that complement the ability of antibodies to destroy pathogens and filter them out of the body. 

4. Inflammatory Response - When a pathogen manages to successfully pass through the anatomical barriers and enter the body, immune system cells such as macrophages release cytokines and histamine. These chemicals triggers an inflammatory response, which manifests as swelling, redness, pain, and sometimes loss of function in the infected area.