Motomi Nakata

Role of Perforin in Lymphocyte-Mediated Cytolysis

Publisher Summary This chapter discusses structure and expression of perforin. Perforin is a primary candidate as mediator of the cellular cytotoxicity exhibited by cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. The granule exocytosis model of lymphocyte-mediated cytolysis, wherein perforin is expected to play a central role, has been proposed on the basis of a great deal of circumstantial evidence. The central role of perforin and universality of the granule exocytosis model have been challenged based on evidence that some CTLs apparently lacking perforin expression are found and that some CTLs and lymphokine-activated killer cells lysed certain target cells without apparent granule exocytosis. The physiological relevance of the perforin-dependent and -independent pathways of lymphocyte-mediated cytolysis, mainly based on recent observations is discussed. The propriety of the perforin/granule exocytosis model has been challenged by extensive studies using various T cell clones, including classical CD8+ CTLs and recently characterized CD4+ helper/killer T cells. Perforin expression in primary CTLs in peritoneal exudate lymphocytes (PELS) after intraperitoneal immunization with allogeneic spleen cells is examined.

Interleukin-2 activated T cells (T-LAK) express CD16 antigen and are triggered to target cell lysis by bispecific antibody

Human PBMCs from healthy donors were cultured with 100 U/ml rIL-2 for up to 5 weeks and tested at short and long activation times for the ability to mediate CD3 and CD16 targeted cytotoxicity using chemically cross-linked bispecific antibodies. At each period, LAK activity was augmented with the use of bispecific antibodies (BA), whereas interestingly enough, at later periods (4-5 weeks) when CD16 positive lymphocytes are not present by flow cytometry, CD16 targeted cytotoxicity was induced. We suspected the possibility of CD16 expression on activated T cells and have purified the T cell subpopulations to see the targeted cytotoxicity. Populations enriched for T cells by Percoll density centrifugation, treatment with anti-CD16 plus complement or sorting for CD5+ cells, were all able to mediate CD16 targeted cytotoxicity following activation with rIL-2. These data suggest that IL-2 activated T cells express CD16 in addition to CD3.