The astounding functions of the immune system.
The first line of defence of our immune system lies within our skin; this frontier is the most apparent part of the immune system that we can see. It serves a vital part in creating a solid physical barrier between the different microorganisms and our body. For the naked eye, the skin might seem as a static simple organ; but in fact it is an elegant complicated structure comprising epidermal cells like keratinocytes and Langerhans cells which recognise foreign antigens. It also contains T-lymphocytes, endothelial cells, tissue macrophages, dendritic cells and mast cells. The keratinocytes on the skin express special receptors called pathogen recognition receptors. As their name suggests; these receptors can identify special arrangements which are universally found on germs and are called pathogen associated molecular patterns (PAMPS). If the skin specialised cells identified a possible threat like a germ or a toxin, this will result in the secretion of antimicrobial and pro-inflammatory mediators. The skin also secretes acidic chemicals which can kill germs. The epithelial cells are tied together with cell tight junctions and cell interactions to prevent pathogens from passing in. They also secrete mucus which, in addition to the epithelial cilia, helps to clear the pathogens away.
Pathogens can gain entry through your nose, mouth and eyes; that is why these organs are covered with mucus which can wash germs away and break their cell wall down by special enzymes like lysozymes. Proteases and gastric acid in the stomach can also destroy pathogens. Nevertheless, in spite of these complicated surface barriers, some germs manage to bypass the first line of defence and enter our body. In doing so, they are instantly confronted with the other vigilant components of the immune system.
The second line of defence is the innate immune system which improves the protection offered by the first line through complement proteins, cytokines, chemokines and different types of inflammatory leukocytes. Cells like macrophages, dendritic cells, mast cells, neutrophils, eosinophils, natural killer cells all play a vital role in innate immunity through recognising and killing bacterial and viral pathogens. In addition, the innate immune system involves membrane-bound receptors that recognise pathogen associated molecular patterns (PAMPs) which are found on a wide range of various microbes.
The third line of defence is adaptive immunity involving T and B lymphocytes. These two types of cells are produced in the bone marrow. B lymphocytes stay and mature in the bone marrow while T lymphocytes leave for the thymus gland, and mature there into T cells. B lymphocytes are highly specialised in producing antibodies against microbes (humoral immunity) and allow our body to remember and recognize previous assailants so that the body can react and destroy them quickly. When antibodies bind a foreign antigen they lead and signal other immune cells to kill and remove the intruder from our body. Immunisation is a controlled way to protect us against infection where our body is exposed to attenuated form of the microbe, thus; B cells secrete antibodies that recognise and neutralise the microbe without having to go through the actual symptoms of the disease. In Immunization our body remember such encounter and acts quickly and promptly upon subsequent exposures to ward off the infection.
Any microbe or foreign particle that dares to breach the first line of defences is faced with notorious challenges inside the body through another sophisticated two lines of defences, that is why although we encounter millions of pathogens around us on daily bases, it is only rarely that our body get infected with any, and bugs are swiftly swiped away by our defence army without us even noticing such incidents. Our Immune system is also vital in helping us fight cancer; a strong immune system can prevent malignancies by destroying viral infections, which can induce certain kinds of cancers. It also kills pathogens and clears any inflammation quickly before it can promote any tumours. The immune system also checks any abnormalities in our cells routinely and destroys any cell that looks suspicious or abnormal before it outgrows and become cancerous