The effects of dietary lipids on gene expression and apoptosis

The immune system protects the body from the constant bombardment of invading micro-organisms and other non-self molecules which could have detrimental effects on the host.A key cell in this protective system is the T lymphocyte, which plays a critical role in determining the type and magnitude of the immune response.Immunoregulation by the T lymphocyte is mediated, in part, by the profile of cytokines (hormone-like molecules) it produces.The fundamental mechanism leading to the propagation of T lymphocytes involves their activation, leading to the production of interleukin (1L)-2 and subsequent proliferation referred to as clonal expansion.Depending on the mode of activation, T lymphocytes will differentiate into either a helper Th-1 or Th-2 cell, as is the case with the CD4+ T lymphocytes, or become a cytotoxic T lymphocyte as with the CD8+ cells.The Th-1 cell produces primarily IL-2, interferon-y, and tumour necrosis factor-a (TNF-a), resulting in enhanced cell-mediated or cytotoxic responses.The Th-2 cell produces IL-4, -5, -6, and -10, generating a humoral or antibodymediated immune response.The T lymphocyte cannot properly differentiate without the help of accessory cells possessing co-stimulatory receptors andlor secreting co-stimulatory cytokines.The two classic accessory cells are the B lymphocyte and the macrophage.Both these cells present antigen to the T lymphocyte, enabling the T lymphocyte to determine the type (e.g.cell-mediated or humoral) of response necessary to successfully defend against the invading agent.This is accomplished with the help of co-stimulatory receptors and molecules produced by both the T lymphocyte and accessory cells.Several co-stimulatory receptors are involved, including intercellular adhesion molecules, lymphocyte-functionassociated antigen, cytotoxic T lymphocyte antigen-4, CD28, B7-1, B7-2, CD2, 0 4 0 and CD40 ligand receptors.Additionally, the accessory cell can produce cytokines such as IL-1 which also assist the T lymphocyte in propagating a response (Abbas et al. 1991).These complex intercellular interactions involve the influence of fatty acid composition of membranes on membrane fluidity, membrane-associated proteins and extracellular receptors which facilitate immune system homeostasis in the host.