Let us explore lymphocyte
recirculation and homing.
So why do lymphocytes
recirculate around the body?
Well, lymphocytes collectively have millions of
different antigen specific receptors - the B-cell
receptor on the surface of the B-lymphocyte, the
T-cell receptor on the surface of the T-lymphocyte.
And therefore, for each antigen specificity, there are
only initially a small number of T-cells and B-cells.
Also the adaptive response requires dendritic
cells in order to activate naïve T-cells.
It needs helper T-cells.
And it needs the cognate B-cells, that is B-cells with the same
antigen specificity as the T-cells to interact with each other.
Lymphocytes therefore need to seek out their antigen,
they need to travel around the body to find antigen.
So they recirculate through the
blood, the lymph nodes, the efferent
lymphatics, and then eventually back to the blood circulation.
Meanwhile dendritic cells can
pick up antigen in the tissues and
migrate via the afferent lymphatics
to the local draining lymph nodes.