Temporal analysis of cytokine gene expression during infiltration of porcine neuronal grafts implanted into the rat brain.

A large array of evidence supports the involvement of infiltrating T lymphocytes in the rejection process of intracerebral neuronal xenografts. Little is known, however, about the molecular mechanisms that drive the recruitment of this cell type. In the present work, we used real-time RT-PCR methodology to investigate the kinetics of cytokine gene expression during the infiltration of fetal porcine neurons (PNEU) implanted into the striatum of LEW.1A rats. T lymphocyte infiltration was followed by measuring the intracerebral levels of transcripts encoding the beta chain of the T cell receptor. These transcripts remained barely detectable until the fourth week (28 days) postimplantation, when a sudden accumulation occurred. Their kinetics, which support previous immunohistochemical observations, indicate that alphabetaT lymphocyte recruitment occurs rapidly after a delay of several weeks in this experimental model. Infiltration of PNEU grafts by T lymphocytes was accompanied by a concomitant, dramatic augmentation of transcripts coding for monocyte chemotactic protein-1 and RANTES (for regulated on activation, normal T cell expressed and secreted), two chemokines targeting this cell type, among others. Likewise, a sudden accumulation of transcripts of proinflammatory lymphokines [interleukin (IL)-1alpha, tumor necrosis factor-alpha, IL-6] as well as Th1 cytokines (IL-2, interferon-gamma) was also detected. In contrast, IL-4, -10, and -13 mRNA remained barely detectable at the different time points. No significant changes were noticed for IL-12 or transforming growth factor-beta transcripts. These data support the concept that T lymphocyte infiltration of PNEU grafts is actively promoted by a local production of chemokines and proinflammatory lymphokines and is based on a Th1 polarization.