The avian lung-associated immune system

The lung is a major target organ for numerous viral and bacterial diseases of poultry. To control this constant threat birds have developed a highly organized lung-associated immune system. In this review the basic features of this system are described and their functional properties discussed. Most prominent in the avian lung is the bronchus-associated lymphoid tissue (BALT) which is located at the junctions between the primary bronchus and the caudal secondary bronchi. BALT nodules are absent in newly hatched birds, but gradually developed into the mature structures found from 6–8 weeks onwards. They are organized into distinct B and T cell areas, frequently comprise germinal centres and are covered by a characteristic follicle-associated epithelium. The interstitial tissue of the parabronchial walls harbours large numbers of tissue macrophages and lymphocytes which are scattered throughout tissue. A striking feature of the avian lung is the low number of macrophages on the respiratory surface under non-inflammatory conditions. Stimulation of the lung by live bacteria but not by a variety of bacterial products elicits a significant efflux of activated macrophages and, depending on the pathogen, of heterophils. In addition to the cellular components humoral defence mechanisms are found on the lung surface including secretory IgA. The compartmentalisation of the immune system in the avian lung into BALT and non BALTregions should be taken into account in studies on the host-pathogen interaction since these structures may have distinct functional properties during an immune response

NK and T cells constitute two major, functionally distinct intestinal epithelial lymphocyte subsets in the chicken

Non-mammalian NK cells have not been characterized in detail; however, their analysis is essential for the understanding of the NK cell receptor phylogeny. As a first step towards defining chicken NK cells, several tissues were screened for the presence of NK cells, phenotypically defined as CD8(+) cells lacking T- or B-lineage specific markers. By this criteria, approximately 30% of CD8(+) intestinal intraepithelial lymphocytes (IEL), but <1% of splenocytes or peripheral blood lymphocytes were defined as NK cells. These CD8(+)CD3(-) IEL were used for the generation of the 28-4 mAb, immunoprecipitating a 35-kDa glycoprotein with a 28-kDa protein core. The CD3 and 28-4 mAb were used to separate IEL into CD3(+) IEL T cells and 28-4(+) cells, both co-expressing the CD8 antigen. During ontogeny, 28-4(+) cells were abundant in the IEL and in the embryonic spleen, where two subsets could be distinguished according to their CD8 and c-kit expression. Most importantly, 28-4(+) IEL lysed NK-sensitive targets, whereas intestinal T cells did not have any spontaneous cytolytic activity. These results define two major, phenotypically and functionally distinct IEL subpopulations, and imply an important role of NK cells in the mucosal immune system

Truth and its uses : deflationism and alethic pluralism

Deflationists believe that the question “What is truth?” should be answered not by means of a metaphysical inquiry into the nature of truth, but by figuring out what use we make of the concept of truth, and the word ‘true’, in practice. This article accepts this methodology, and it thereby rejects pluralism about truth that is driven by ontological considerations. However, it shows that there are practical considerations for a pluralism about truth, formulated at the level of use. The theory expounded by this article states that truth is a dual-purpose tool; it can be used as a device for transferring justificatory burdens and, for select areas of discourse, it can also be used as a standard, a norm. This contrast in how truth is used introduces a bifurcation in our discourse that is reminiscent of metaphysical divides traced by more traditional versions of alethic pluralism. However, my pluralism “at the level of use” states that truth is plural solely at the level of use. It is unified at both the conceptual as well as the metaphysical level. At those levels, the theory takes its cue from deflationism. As such, this theory is offered as a midway point and as a potential way forward in the debate between deflationism and pluralism.Publisher PDFPeer reviewe

Alethic pluralism for pragmatists

Pragmatism and the correspondence theory of truth are longtime foes. Nevertheless, there is an argument to be made that pragmatists must embrace truth as correspondence. I show that there is a distinctive pragmatic utility to taking truth to be correspondence, and I argue that it would be inconsistent for pragmatists to accept the utility of the belief that truth is correspondence while resisting the premise that this belief is correct. In order to show how pragmatists can embrace truth as correspondence, I develop a kind of alethic pluralism, which treats pragmatist truth as theoretically fundamental to truth as correspondence. This theoretical fundamentality of pragmatist truth allows the pragmatist to conditionally accept truth as correspondence for certain discourses without falling prey to the typical pragmatist objections to correspondence. This pluralist account of truth thus allows pragmatists to concede that, for certain domains of discourse, truth is correspondence, without thereby betraying their pragmatist principles.Publisher PDFPeer reviewe

Synthesis of IFN-β by Virus-Infected Chicken Embryo Cells Demonstrated with Specific Antisera and a New Bioassay

Transcripts of interferon-α(IFN-α) and IFN-β genes are present in virus-infected chicken cells, but because of a lack of appropriate assays and reagents, it was unclear if biologically active IFN-β is secreted. We have established a nonviral bioassay for the sensitive detection of chicken IFN (ChIFN). This assay is based on a quail cell line that carries a luciferase gene that is controlled by the IFN-responsive chicken Mx promoter. Luciferase activity was strongly stimulated when the indicator cells were incubated with ChIFN-α, ChIFN-β, or ChIFN-γ but not with chicken interleukin-1β (ChIL-1β). Unlike the classic antiviral assay that preferentially detects ChIFN-α, the Mx-luciferase assay detected ChIFN-α and ChIFN-β with similar sensitivity. With the help of this novel assay and with rabbit antisera specific for either IFN-α or IFN-β, we analyzed the composition of IFN in supernatants of virus-infected chicken embryo cells. Virtually all IFN produced in response to Newcastle disease virus (NDV) was IFN-α. However, IFN produced in response to influenza A or vaccinia virus (VV) was a mixture of usually more than 80% IFN-α and up to 20% IFN-β. Thus, IFN-α and IFN-β both contribute to the cytokine activity in supernatants of virus-infected chicken cells. Furthermore, the infecting virus appears to determine the IFN subtype composition