And the most common ways by which pathogens enter our body is through the simple process of breathing when we exchange air inside our lungs that can bring different types of pathogens into our body. Pathogens can also enter our body through the food that we eat, through the water that we drink or through some type of cut that is found on our skin. Now, in order for our immune system to actually be effective and efficient, it must have a way to actually differentiate, to actually distinguish between its own cells of the body and these foreign pathogens that can cause harm to those cells of the body. Now, such recognition is actually possible because the cells of our body contain special unique macromolecules. For example, proteins or lipoproteins that are found on the membrane of the cells of the body. And our immune system can use these unique biological molecules on the membrane to recognize its own cells.