L is for lytic granules: lysosomes that kill.

CTL are important cells in the immune system which are able to recognise and directly destroy virally infected, tumorigenic or foreign cells. The proteins which mediate this destruction are packaged into specialised secretory granules, termed lytic granules, which are secreted in response to target cell recognition. Curiously these specialised secretory granules also contain all the lysosomal hydrolases, and in CTL the lytic granules serve two separate functions: as a lysosome within the cell, and as a secretory granule when a target cell is recognised.

Perforin is activated by a proteolytic cleavage during biosynthesis which reveals a phospholipid-binding C2 domain.

Perforin is a secreted protein synthesized by activated cytotoxic T lymphocytes (CTL) and natural killer (NK) cells. It is a key component of the lytic machinery of these cells, being able to insert into the plasma membrane of targeted cells, forming a pore which leads to their destruction. Here we analyse the synthesis, processing and intracellular transport of perforin in the NK cell line YT.

Fc gamma receptor II dependency of enhanced presentation of major histocompatibility complex class II peptides by a B cell lymphoma.

Here we show that the B cell lymphoma A20.292 is capable of enhanced antigen presentation to CD4+ T cells in the presence of specific antibodies. This enhancement was inhibited by anti-Fc gamma receptor (R) antibodies, suggesting that it might be due to preferential uptake of the antigen/antibody complex through the Fc gamma RII receptor.