The first line of defence is a non-specific, defence system that involves a number of features such as tears that, with the aid of enzymes such as lysosomes prevent entry of the pathogen into the body through the eyes.
The intact skin acts as a barrier; which we constantly shed cells from in order to prevent entry of microorganisms. It is a good barrier because the skin is very dry and tough and generally a very inhospitable environment for organisms to grow on. Sweat on the surface of the skin contains enzymes, such as lysosomes which can kill pathogens that attempt to enter the body. The picture below is able to show how the skin prevents the entry of pathogens with the assistance of sweat by digesting and washing away said foreign pathogens.
Another example of a barrier in thr first line of defense would be mucous membranes that are able to trap pathogens, and then expel them through the organism coughing and sneezing. The image below shows the variety of mucous membranes in the mouth and the other shows one of the actions in which the pathogen can be expelled once trapped.
Some other ways that the body's first line of defense aids in the immune system are secretions such as saliva, , acids in the stomach/vagina and also the mucous itself. Once the foreign pathogen has been trapped, human reflexes that include; vomiting, urination and Cilia that is constantly sweeping pathogens out of the lungs.