Nature's defense mechanism

The human body is a complex machine. Made up of billions of cells which interact with one another regularly, the human body, yet it works more perfectly than any other machine made by man. It is not that the human body does not face any threats to its normal function, but it has its own mechanism for thwarting any condition that could lead to its breakdown. This can be seen explicitly in the case of DNA replication, the most important activity performed by cells. If the DNA is not replicated faithfully, it would lead to mutation and eventually the extinction of the species. But DNA polymerases, proteins that are responsible for DNA replication, do make mistakes. These errors are corrected by an error-correction mechanism, making the process of DNA replication highly efficient.

Though these errors are a hurdle to the normal cellular activity the most dangerous threat is the invasion by foreign bodies. In order to fight these foreign bodies the human body has the immune system (the fascinating natural defense of the human body).

In this post I am not going to be talking about the classification of the immune system, the types of cells involved or its mechanism of action. I am sure the Wikipedia page on the Immune System is a good source for understanding the basics. The immune system on the surface looks very complex. But with the help my crude understanding I am going to take a simplistic route to describe all its features that fascinate me.

• The very structure of the immune system is beautiful. It is analogous to the structure of an army. It has the non-specialized cells as the first line of defense which is similar to the infantry in the human army. If the enemy gets through the first line of defense, then it encounters the more specialized units. This is evolution at its best - figuring out the best way to defend the body.

• The immune cells, after they are formed, go through an elaborate development process where they are educated to distinguish between what is self and what is foreign. The similarity between this development process to the education imparted in a defense school is not just an analogy but the cells are literally educated.

• The immune system can 'remember' any attacks from the past and learns from it such that a similar attack doesn't happen again. The more I describe the immune system the more one can see how similar it is to an army!

• The immune system deploys one of its specialized cells called the T cell when the invading foreign bodies get through the first line of defense. These T cells have surface receptors that specifically recognize a different type of foreign body. That is, there is one T cell for each type of foreign body. The type of the receptor depends on the type of gene that is expressed. Imagine the number of genes that would be required if there is a different receptor for each foreign body. But the body mixes and matches a handful of genes to create a large pool of genes. What a wonderful strategy!

• There are various types of immune cells. Recent research shows these cells look different on the surface but they are the same cells changing from one type to another depending on their environment with time. This is similar to what the standard model of particle physics says about particles and forces. An instant after the universe was formed, all the particles and forces were indistinguishable. With time they became different. This is exciting because one day the immune system could have its own standard model and its complexity could finally be tamed.