Effector population

Yamamoto J, Adachi Y, Onoue Y, et al. Differential expression of the chemokine receptors by the Thl- and Th2-type effector populations within circulating CD4+ T cells. J Leukoc Biol 2000 68 568-574. 

Hapten-specific CD8+ T lymphocytes, likely the major effector population, are directly cytotoxic to chemical exposed keratinocytes and also release cytokines that boost the inflammatory response. In addition, Thl cells release a number of cytokines and chemokines that promote inflammation and activate mast cells and, in the presence of IFNy, are also capable of killing keratinocytes. Although the hapten may persist in skin for some time, this reaction is self-limited. CD4+ regulatory T cells that secrete IL-10 (similar to those described in relation to UV-induced immune suppression in Section 32.4.3) appear to play an important role in this regulation. 

CROFT, M CARTER, L SWAIN, S.L. DUTTON, R.W. (1994) Generation of polarized antigen-specific CD8 effector populations reciprocal action of interleukin (IL)-4 and IL-12 in promoting type 2 versus type 1 cytokine profiles. Journal of Experimental Medicine, 180,1715-1728. 

FIGURE 15.9 Monod-Wyman-Changeux (MWC) model for allosteric transitions. Consider a dimeric protein that can exist in either of two conformational states, R or T. Each subunit in the dimer has a binding site for substrate S and an allosteric effector site, F. The promoters are symmetrically related to one another in the protein, and symmetry is conserved regardless of the conformational state of the protein. The different states of the protein, with or without bound ligand, are linked to one another through the various equilibria. Thus, the relative population of protein molecules in the R or T state is a function of these equilibria and the concentration of the various ligands, substrate (S), and effectors (which bind at f- or Fj ). As [S] is increased, the T/R equilibrium shifts in favor of an increased proportion of R-conformers in the total population (that is, more protein molecules in the R conformational state). 

A distinct population of effector T cells that promote tissue inflammation has been described without suppressive functions [9]. This population is termed as Th9 cells and exerts IL-9 and IL-10 secretion capacities. IL-4 and TGF-(I promotes an IL-9-producing subset, Th9 cells, which have roles in mucus production and tissue inflammation [100,101]. 

If the control problem is of modest scale, the number of distinct classifiers may be sufficiently small that every possible variant can be included in the initial population however, for a system of even moderate size, with just a few inputs and effectors, this is a forlorn hope. 

The effects of Pb on the mixed lymphocyte response (MLR) have been examined in prior studies. McCabe and colleagues [53] and Farrer and colleagues [54] demonstrated that Pb in vitro at very low concentrations (0.1 pM = 2 pg/dL) significantly enhanced the proliferation and expansion of murine alloreactive CD4+ T lymphocytes in the MLR. The expanded T cell population was found to have a high density of CD4 molecules on the cell surface making them phenotypically similar to memory/effector T lymphocytes. In a study using Lewis strain rats, Razani-Boroujerdi and coworkers [55] also found evidence for Pb-induced stimulation of the in vitro MLR. 

Although closely related, monocytes/macrophages (MO) possess features that are distinct from DCs. Due to their limited expression of T-cell costimulatory molecules, MO are not able to prime T cells de novo, but rather stimulate effector/memory T cells by the secretion of cytokines, which support T-cell proliferation. As DCs, MO differentiate from myeloid precursors and form a heterogeneous population of antigen-presenting cells (APCs) that link the innate and adaptive immune systems. However, their ability to interact with T cells via MHC class II TCR interaction(s) as well as engagement of T-cell costimulatory receptors on their surface, makes close contact between MO and Tregs likely to occur in vivo. 

Natural killer (NK) cells are bone marrow-derived large granular lymphocytes playing an important role in the innate immunity, especially against viruses and tumor cells, and they form 10-15% of the total lymphocyte population. NK cells have the ability to lyse cells without specific antigen recognition, and these cells may be considered as effector cells, especially in the innate... 

Recent developments in immunology now offer a conceptual framework to understand the link between helminth infection and immunomodu-lation. Parasites induce Treg populations which suppress antiparasite effector cells, as part of the parasites own strategy for survival in the host. At... 

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