Topic 2 lecture note..

lymphoid organs is inhibited, and injection of NAD(P) into mice markedly decreases T
cell homing. Note: 41 is not ADP-ribosylated, and B cells don’t express ART2, hence
their homing is not affected.
Ectopeptidases regulate chemokines
CD26 is an ectoenzyme that cleaves N-terminal dipeptides containing either proline or
alanine residues from polypeptides. CD26 is expressed de novo on activated T and B
cells, NK cells, and endothelial cells. Numerous bioactive peptides are cleaved by CD26,
including chemokines. Cleavage of chemokines by CD26 reduces their ability to bind and
activate chemokine receptors, whereas their ability to serve as chemoattracts can be
enhanced (eg CCL5). Rodents that are deficient in CD26 have increased infiltration of
leukocytes into the lung and joints in models of asthma and arthritis, suggesting that
CD26 plays a role in inhibiting inflammation.
Sheddases
CD156b is a sheddase that cleaves L-selectin from the surface of thymocytes. Other
sheddases are also involved. L-selectin is shed from lymphocytes to prevent re-entry of
activated T cells to secondary lymphoid organs.
Ectoenzymes in the control of leukocyte traffic
The nucleotidases CD39 and CD73 regulate the balance of ATP and adenosine, and the
activation of leukocyte integrins and vascular cell adhesion molecules. CD26
proteolytically modifies the activities of chemokines, whereas sheddases cleave leukocyte
cell adhesion molecules such as L-selectin. ADP ribosyltransferases such as ART2
modify and inactivate adhesion molecules.