Terry M. Bella
Vaccines are stimulants used to generate the production of antibodies by our immune system. Antibodies are produced by our B-cells, the major player of our humoral immune system. Antibodies are our body’s specific and targeted defense against pathogens and are fundamentally important to our health. The stimulant is a pathogen specific antigen. Pathogens may have several antigens. The antigen itself, recall, is just something that identifies a pathogen and by itself does not pose the threat of disease.
The human immune system has components that are innate and adaptive. Adaptive immunity has specificity wherein innate does not. This specificity, wherein the immune system has the ability to respond with a specific response (antibodies) to a specific invasion, will be discussed further below. Firstly though, innate immunity is comprised of attributes such as skin, mucous membranes, and secretions. Skin, the integumentary system, is considered a first line of defense for the body, hence part of the immune system. Skin is non-specific, the purpose to simply be a physical barrier separating the inside of the body from the outside world. Every bit of your body that is exposed to outside is lined with skin. Consider that when you consume food that that food travels through what is essentially a tube that passes from one end of the body to the other, seemingly through the body, yet the food does not come into direct contact with the body interior. The tube is lined with skin the entire way. The nutrients and water that the food contains must be broken down to the molecular level in order to pass through the lining of lining. Only then is something actually entering the body. Consider also how important it is to clean and sanitize a wound as it is a breach in the skin barrier. Skin, like mucous membranes and secretions, is non-specific because it treats all foreign material the same, no passage is allowed unless at the molecular level.
Internally we have phagocytic cells, antimicrobial proteins, the inflammatory response, and natural killer cells all of which are part of the innate immune system. Again, this system lacks specificity and is simply a response to an invasion or compromise of the body. There is a bridge between the innate and the adaptive carried out by the phagocytic such as dendritic cells.
Adaptive immunity is broken into two factions, cell-mediated and humoral. Adaptive immunity is called as such because it has the capacity to adapt, developing responses to pathogens based on an antigen recognition system. The dendritic cell, a player of the innate immune response communicates with the adaptive immune response via cell-mediated immunity. Dendritic cells patrol the body, within the bloodstream and even sometimes in interstitial spaces, looking for any material that is foreign to the body. Dendritic cells are non-specific and are seeking material that presents molecules common to bacteria and material presented by cells infected by a virus. These are taken by phagocytic action. Dendritic cells work with T-cells which are part of the cell-mediated immune system. Dendritic cells work with T-cells by presenting antigens to them. They are referred to as antigen presenting cells (APC’s). These antigens are obtained by sequestering and digesting foreign material. This is where the magic of the vaccine can first be understood. We have immune system players that not only destroy that which threatens the body but also have the functionality to display how to recognize it, its antigen, in order to communicate with the adaptive immune system, thus resulting in a teaching/learning process. The premise behind how a vaccine works is that we have an immune system that can learn, hence adapt.
Cell-mediated immunity communicates with the humoral response via helper T-cells. Helper T-cells will “share” antigen information with B-cells of the humoral system. B-cells develop antibodies specific to the antigen. The antibodies are the defense, attaching to a specific antigen. The antibody attachment stops the action of the pathogen through one of multiple ways. Some antibodies neutralize the pathogen, while others increase phagocytosis. There are other more complex effects but they are beyond the scope of this unit. Cell-mediated immunity develops memory T-cells to prepare for future infections by anything bearing the same antigen and the humoral system generates memory B-cells for future infections as well. The humoral response is about creating and storing antibodies specific to the antigen. These antibodies will be carried in and released by plasma cells when needed. A vaccine is a method of delivering an antigen in a safe way to the cell-mediated system so that the body can learn about and prepare for the antigen. The vaccine is simply a way to leverage the immunological response that we all have.
When vaccines are delivered they are targeting lymphocytes, those phagocytic cells of the immune system such as dendritic cells. Vaccines are delivered into muscle tissue because it is more likely that the lymphocyte will find the “pathogen” in this area as opposed to in the blood stream. Somatic cells, such as the muscle tissue cells, may also take in the vaccine and present the antigen to a T-cell. This presentation, when effective, is presented on a major histocompatibility complex (MHC). These are extracellular surface level proteins that present antigens to T-cells. There are two classes of MHC molecules. Class 1 MHC’s are utilized by most all nucleated cells of the body and are recognized primarily by cytotoxic T-cells. Cytotoxic T-cells have the capability of destroying cells as well as activating more cytotoxic T-cells and memory T-cells. Class 2 MHC’s are used by the APC’s and are recognized by cytotoxic T-cells and helper T-cells. APC’s are the dendritic cells, macrophages, and B-cells.
I have presented a relatively brief overview of the immunes system, how it is organized and how some action and communication occurs. Just this cursory look at the system is still confusing. The goal in the high school classroom is that students understand that the immune system is complex because it involves many layers of defense with many different cell types and that the system is adaptable, allowing for the use of vaccines. High school students need to gain an understanding of the method of presenting a fragment of a pathogen to the immune system so that the immune system can prepare a defense in the case that the actual pathogen infects the body. The defense is primarily antibodies, produced by B-cells based on information provided by other B-cells, helper T-cells, or a phagocytic lymphocyte. Ultimately the understanding is crucial to the student’s comprehension of vaccine technology as a way to leverage the immune system to fight off infection as opposed to introducing chemicals to the body, medicine, in order to kill off an infection. It is also imperative that students understand that a vaccine is not infecting the body, but simply showing the body what the infecting agent will look like.
Furthermore, there is room in this unit to focus on the biology concept of structure equals function. The structure of the antigen is what the entire defense is based upon. Antigens are proteins and thus have a defined structure. Receptors and antibodies that bind to antigens are doing so based upon the structure of the antigen. This concept can be tied back to other units in the curriculum concerning cell to cell recognition and cell transport. Considering that antigens are proteins will help students to understand the difficulties of storage and transport of vaccines which is discussed later in this unit.
