Before we get into what an antibody is and what it can do, let's revisit the human immune system. Did you know that, anatomically speaking, there is no separate and distinct 'immune system' as such (unlike other systems such as the circulatory system or the respiratory system)? Instead, there are several systems that possess immune function, the most important of which is the digestive system, as it is home to our microbiome or 2nd brain.