In vitro generated allospecific cytolytic T lymphocytes injure pancreatic islets

The role of cytotoxic T lymphocytes in the rejection of pancreatic islet allografts remains poorly defined. The present study was designed to assess the ability of in vitro generated cytolytic T lymphocytes to produce allospecific functional and structural damage of mouse pancreatic islets. A mixed lymphocyte-islet coculture model (MLIC) has been developed, in which islets from DBA/2J mice (H-2d) stimulate the generation of allospecific cytolytic T lymphocytes (C57B1/6, H-2b), as measured by lysis of allospecific chromium-labeled tumor targets. Responder C57B1/6 splenocytes sensitized to DBA/2J islets were harvested from the MLIC on Day 5 and cocultured with either freshly isolated DBA/2J or B10.BR (H-2K) islets. Islet injury was determined by assessment of beta cell function after 8 hr (as measured by insulin release in response to a glucose challenge) and islet destruction after 24 hr of coculture with the sensitized splenocytes. Whereas coculture of third party B10.BR islets with MLIC-sensitized C57B1/6 anti-DBA splenocytes had no effect on insulin release or structure, incubation of allospecific DBA/2J islets with these splenocytes resulted in inhibition of insulin release after 8 hr and disintegration of the islets by 24 hr. The depletion of MLIC-sensitized C57B1/6 anti-DBA splenocytes with anti-Lyt2 monoclonal antibody, but not anti-L3T4 monoclonal antibody, prevented the allospecific destruction of fresh islets by the splenocytes in culture. This study suggests that allospecific, cytotoxic T lymphocytes may play an important role in the effector mechanism of pancreatic islet allograft destruction.