..You
receive a cut...Bacteria
enter the wound...Many
are destroyed rapidly by complement and the phagocytes recruited through
acute inflammation (innate immunity)...Some
of the dead bacteria or their breakdown products are taken up by the
tissue resident dendritic cells...The
combined action of bacterial products and cytokines (from acute
inflammation etc.) activate the tissue dendritic cells...This
causes them to migrate to the local lymph node via afferent lymphatics...Dendritic
cells enter the node in the T cell areas. They become resident there
displaying their 'wares'..T
cells enter the node from the blood, trafficking through the T cell area
to the efferent lymph. Those which recognise the bacterial antigenic
peptides displayed on the dendritic cells stop, activate, divide and
differentiate; some later become memory T cells...B
cells entering nodes from the blood must cross the T rich area in transit
to the B cell rich areas. The antigen-specific ones must acquire antigen
too, presumably via the lymph. Then they can have their MHC-peptide
complexes recognised by activated T cells and receive help...Some
become IgM secreting plasma cells. Some migrate to the B cell rich areas
and form germinal centres. Here B cells proliferate and give rise to
progeny with high affinity for antigen through a process called affinity
maturation. The products of germinal centres become IgG,A etc plasma cells
and memory B cells.
Information provided by: http://www-immuno.path.cam.ac.uk