Question

Explain clonal selection and how it works to protect you against many different infectious agents.

Answer 1

• Clonal Selection:

Our adaptive immune system is made up of B cells and T cells. B cells when give rise to daughter B cells, each of them are different from one another as well as from the ancestor B cell. So, even their receptors (BCR) which later on form antibodies are different from one another. This makes them have different antigen specificities. So a cell pool of various kinds of B cells (or you may say, BCR/antibodies) are generated when B cells divide. Later on, when a foreign substance/antigen/pathogen enters our system, a specific B cell is selected which can exactly recognize and work on that specific antigen. That special B cell already existed in the pool but now that it is selected, its clones can be made to eliminate the antigen. The same thing occurs for T cells as well. This "selection" is called clonal selection.

• How clonal selection works to protect you against many different infectious agents:

The process is explained below step by step:

1. When our immune system develops gradually, B and T cells are formed and then they are matured/proliferated in the bone marrow and thymus gland respectively. As they are dividing, B cells give rise to various different kinds of B cells with different receptors which have different antigen-specificities. T cells also do the same, they produce various type of T cells with different TCR. This division occurs randomly and the differences in the receptors also are random. So, a variety of B and T cells are produced and kept in our system.
2. There are several types of pathogens, foreign harmful substances, infectious agents everywhere. Their surfaces are coated with different types of proteins. But we already have different immune cells with various specificities in our system. Now, when any infectious agent enters our system, the B cells recognize or interact with them directly and only a specific B cell recognizes that agent (because it has the specificity exclusively for that antigen). Same thing occurs in case of T cells too, except the fact that T cells do not interact with antigens directly, rather antigen presenting cells (APC) help them with it by giving a small piece of antigen protein (epitope/antigenic determinant) which the T cell can recognize. So, that B/T cell is selected because that is needed to fight the infection.
3. Now that special B/T cell starts dividing rapidly to develop more and more B/T cells with same BCR/TCR i.e.., prepare clones of that specific B/T cell. Some of them become effector cells and make antibodies to eliminate the infection immediately. Some become memory cells so that next time the infectious agent invades, infection is prevented immediately.