Question

Describe the cascade of events that happen to our pre-b-cells when they come in contact with an E. coli cell in the blood stream.

Answer 1

B cells, also known as B lymphocytes, are a type of white blood cell . They provide immunity to our body by secreting antibodies. The pre B cells are developed from the pro B cells and contain membrane bound antibodies. Pro-B cells become pre-B cells when they express membrane m (heavy)chains with surrogate light chains in the pre-B receptor. Surrogate L chains are similar to actual L chains but are the same on every pre-B cell.

Given below is the structure of an antibody showing two heavy chains (blue) and two light chains (green). The constant and variable parts are also indicated with C and V markings.

During the pre-B cell stage HC Ig ( heavy chain immunoglobulin) gene rearrangement is completed and tested and light chain (LC) gene rearrangement takes place to generate a fully functional B cell receptor (BCR, which is a membrane bound antibody). As both chains are present in the pre B cell, their immune response will be similar to the B cell.

The immunoglobulins, or membrane bound antibodies on the cell membrane has a variable portion which exhibits great diversity, to the range of 10 billion types. There are combinations which bind to a wide variety of receptors on the surface of a bacteria, virus or a foreign protein. When such a cell comes in contact with E. Coli in the blood stream, one particular type of B-cell will bind to the receptors on the pathogen.

This B cell will then be activated with the help of a T cell.

The B cell now starts cloning itself and generates multiple versions of the same type of cell.

Next the differentiation process starts and the cloned cells take on various roles. Some become memory cells, which will respond much faster if they come in contact with E. Coli in future. Some turn into effector cells which produce antibodies and release them into blood stream. An activated effector cell can produce upto 2000 antibodies per second.

These antibodies start bonding to the pathogen and tags them for pickup by phagocytes, a process called opsonizatin.

As each B cell has two heavy chains and two light chains, each of their variable portions can bond to epitopes of the antigen and help in nullifying them as well.