HUMORAL IMMUNITY

Now it is time to look at B-cell lymphocytes.

These B-cell lymphocytes give rise to the type of immunity that we call HUMORAL IMMUNITY.

This immunity is called humoral immunity because the effective components of this part of the immune system are soluble in tissue and plasma fluid, rather than being cells.

In many ways, the B-lymphocytes can be thought of as the infantry and artillery regiments of our immune army.

They do much of the hard work byshooting off the long range 'missiles' - otherwise known as antibodies - which often start the downfall of the invading micro-organisms.

So, to start at the beginning, the B-lymphocytes, like the other blood cells, begin life as immature stem cells in the bone marrow.

Unlike the T-lymphocytes, however, they also mature and proliferate in the bone marrow (remember B-cells from Bone Marrow).

Now the B-cells, like so many of us, are rather lazy beings just enjoying a quiet life with their feet up and watching the world go by.

Even when our bodies are attacked by invaders such as bacteria, most of them will not do anything about it until they are given a metaphorical 'kick up the backside' by the sergeant majors of the immune system - the T-helper lymphocytes.

These stimulate most of the B-lymphocytes to proliferate and to undergo a change into PLASMA CELLS.

This the T-helper lymphocytes do by means of various chemicals.

The Plasma Cells then manufacture the relevant antibodies (properly known as IMMUNOGLOBULINS) which are attached to their surfaces, rather like guided missiles.

These immunoglobulins perform several functions.

Some stimulate the complement system into action, whilst others attach themselves to the invading micro-organisms so that the T-cytotoxic, NK cells and phagocytes can in turn become attached to the other end of the immunoglobulin.

In this way the antigen (invading micro-organism) becomes attached to the phagocyte (or to other killer cells) rather like a stamp hinge acting as an anchor for both the stamp and the page of a stamp album - click on icon below.

In other words, the immunoglobulin acts as a bridge holding both the phagocytic cell/killer cell and the micro-organism until the micro-organism can be destroyed.

Once the invading micro-organisms have been destroyed, the B-lymphocytes and Plasma Cells, who are somewhat lacking in intelligence, are left without an enemy to fight.

Therefore, rather like certain so-called football supporters who are only there for a 'punch-up', if they are not stopped, they will turn on the body's own cells and may try to destroy them.

Therefore we need to call out the 'Military Police' - the T-suppressor lymphocytes - to quietly and gently persuade them to go home.

We can simply summarise this by saying that the T-helper lymphocytes stimulate the B-lymphocytes to switch on the increased production of the correct antibodies, whilst the T-suppressor lymphocytes switch off the excess B-cell production once the antigens have been destroyed until the next time we are threatened by an invading army of pathogens.