Immunity: Adaptive versus Innate Immunity

Innate Immunity

Innate immunity is the immunity you are born with. It includes both physical barriers such as the skinThe body’s largest organ, providing protection and regulation. and internal defenses. Internal defenses include cellular defenses performed by phagocytes and natural killer cellsThe basic structural and functional units of life., as well as inflammation, antimicrobial proteinsLarge molecules made of amino acids with various functions in the body., and fever. Innate immunity relies on two broad categories of cells for defense: phagocytes and natural killer cells. As we discussed, phagocytes destroy pathogens by engulfing them in vesicles. Then, they break them down. Finally, they spit out the remains.

Innate immunity is your first line of defense. This defense begins with your skin and mucous membranes. But what happens if you get a cut that breaches the skin’s defenses, and it gets infected? At that point, the internal defenses take over, using immune cells and chemicals to attack invading pathogens.

The arsenal of chemical weapons includes the inflammatory response, the secretionThe process of moving substances from the blood into the nephron tubule to be excreted in urine. of antimicrobial proteins, and fever.

Adaptive Immunity

Adaptive immunity is the body’s specific immunity. Unlike your innate immunity, which is nonspecific, it attacks anything it recognizes as foreign, damaged, or unknown. Adaptive immunity is very choosy. Adaptive immunity will only attack specific threats. Adaptive immunity is carried out by two types of lymphocytes, the B cells and the T cells. Like all blood cells, the lymphocytes first develop in the bone marrow. B cells stay and mature there. Immature T cells migrate to the thymus where they mature. These lymphocytes become immunocompetent and have to be self-tolerant. In other words, these cells need to evoke an immune response. They must ensure that response isn’t against your own normal cells.

Adaptive immunity has three underlying traits. First, it is specific. It recognizes and attacks only specific pathogens. Secondly, it is systemic. This is a widespread reaction, not limited to a localized region of the body. Lastly, adaptive immunity has memoryThe ability to store and recall information.. In many cases, once you are exposed to a virus, your body remembers and you become resistant to reinfection.

Adaptive Immunity

There are four general phases of adaptive immunity. These phases reflect more specific cellular processes in the lymph nodes.  First, the pathogen has to gain entry and pass all those innate defenses.  This can take 5 to 7 days.  The next phase occurs when your body recognizes that there is an infection. Your body then decides what to do about it.  This can take 2-3 days.  Then, for about 2 weeks, your T cells and B cells mount their attack on the pathogen.  This is the adaptive immune response that clears the pathogen from your body.  But, we’re not done yet.  We have to establish memory, which is the basis of adaptive immunity.  Your cells remember for next time.

Immunity

Let’s summarize what we have learned in order to contrast innate immunity and adaptive immunity. Innate immunity can also be called general immunity. It responds very quickly to invasion by a pathogen. However, it is very non-specific. Pathogens are recognized as being not self-antigens. Their specific identity doesn’t matter for immune cells such as neutrophils and macrophages. Innate immunity involves cells that secrete chemicals called cytokines that then coordinate with adaptive immunity. It’s very difficult to tease apart innate and adaptive immunity. This is because it’s never like one of them works alone. They both work together. Your innate defenses coordinate with your adaptive defenses. By doing so, they result in clearance of the pathogen or removal of the infectious agent. Notice that adaptive immunity at the bottom has one more step that’s a bit different from innate immunity. Adaptive immunity also called specific immunity is for your long term defenses little sleep because it creates memory cells. What also differentiates adaptive immunity from innate immunity is the stimulation of B&T cells. These very specific lymphocytes respond to limited numbers of epitopes. These lymphocytes are also capable of migrating to the infection site to perform pathogen clearance.