Immunology: your life depends on it

The mechanisms employed by the human body to destroy and to resist pathogen infection are simply breathtaking. The field of immunology is vast, and often taken for granted by the less inquisitive of our race, so my aim for this post is to dispel any doubt about how vital our immune system is, and perhaps put the fear of the fictional god in your heart. Let's start with the basics: most mammalian immune systems are split into 2 tiers: the innate and adaptive immune systems. The innate response is usually triggered by pathogens being detected by pattern recognition receptors, which respond to generic microorganism components or the cries for help from body cells. The innate immune system is therefore non-specific, so it does not produce antibodies, but it can act on a wide range of microbes, making it the first and main line of defence against disease in the human body. There are multiple components to this immune system; surface barriers like our skin and mucus,  mechanical barriers like coughing up mucus filled with pathogens to protect the lungs and respiratory tract and biological barriers, like the gut flora in our intestines which competes against parasitic pathogens. Inflammation in response to injury is also part of the innate system; compromised cells release signalling molecules (like cytokines) to dilate blood vessels and attract white bloods cells (leukocytes), specifically phagocytes, which digest the invading pathogens. The mammalian complement system is is another vital part of this response. Essentially, complement proteins bind to carbohydrate receptors on the surface of microbes, triggering a cascade of protease-like molecules which break down the surface of a microbe, rendering it inactive. It's a bit like the body's version of a gatling gun. The final elements of the innate system are the natural killer cells, which detect cells with low levels of a surface marker called MHC, meaning the cells are infected or cancerous, and they are destroyed. NK cells aren't concerned about trivial things like collateral damage... 
Let's now move on to the adaptive immune system, which is definitely my favourite, if you can have a favourite layer of the immune system. It is more potent, and is capable of remembering microbes because of their signature antigens, to speed up immune response. Therefore the adaptive immune system is antigen specific, so can recognise specific antigens in antigen presentation of cells. This system employs more variants of leukocytes, known as lymphocyte B cells and T cells. The B cells produce antibodies to target specific antigens on microbes, causing them to bind together, making it easier for phagocytosis to occur. The T kills can split into 2 kinds: T helper cells and T killer cells. T killer cells kill cells infected with pathogens (viruses in particular), and each one recognises a specific antigen (like everything in this system). When activated T killer cells release cytotoxins into compromised cells, inducing apoptosis. How neat. T helper cells regulate the immune response, by directing other cells to perform immunological tasks like digesting pathogens or producing antibodies. The most impressive thing about B and T cells is that their daughter cells can become long-lived memory cells, which remember specific antigens encountered in the past, and so can produce a particularly powerful immune response if that antigen is detected in the body again. Just from this brief overview of the immune system (trust me, this is heavily summarised), I hope you can see how vital every mechanism is to our health. Your heart may keep blood flowing around your body, your lungs may be the centre of gas exchange, but they would be meaningless without the protection the immune system affords your body. Next post I'll be describing what happens when the immune system fails. Trust me, it will be terrifying.