Long-term persistence of Ag-experienced CD8 cells, a class of T lymphocytes with cytotoxic function, contributes to immunological memory against intracellular pathogens. After Ag clearance, memory CD8 cells are maintained over time by a slow proliferation, primarily cytokine driven. In this article, we show that the bone marrow (BM) is the crucial organ where such basal division of memory CD8 cells occurs. BM memory CD8 cells contain a higher percentage of proliferating cells than their corresponding cells in either spleen or lymph nodes from C57BL/6 mice. This occurs both in the case of memory-phenotype CD44high CD8 cells and in the case of Ag-specific memory CD8 cells. Importantly, the absolute number of Ag-specific memory CD8 cells dividing in the BM largely exceeds that in spleen, lymph nodes, liver, and lung taken together. In the BM, Ag-specific memory CD8 cells express lower levels of CD127, i.e., the α-chain of IL-7R, than in either spleen or lymph nodes. We interpret these results as indirect evidence that Ag-specific memory CD8 cells receive proliferative signals by IL-7 and/or IL-15 in the BM and propose that the BM acts as a saturable “niche” for the Ag-independent proliferation of memory CD8 cells. Taken together, our novel findings indicate that the BM plays a relevant role in the maintenance of cytotoxic T cell memory, in addition to its previously described involvement in long-term Ab responses.
The CD4 and CD8 molecules are transmembrane glycoproteins expressed by functionally distinct subsets of mature T cells. CD4+ and CD8+ T cells recognize antigens on major histocompatibility complex (MHC) class II-bearing and class I-bearing target cells respectively. The ability of monoclonal antibodies against CD4 and CD8 to block antigen recognition by T cells, as well as cell-cell adhesion assays, indicate that CD4 and CD8 bind to nonpolymorphic determinants of class II or class I MHC. Here we demonstrate that soluble recombinant HLA-DR4 molecules from insect cells and HLA-DR-derived peptides bind to immobilized recombinant soluble CD4. CD4 binds recombinant soluble DR4 heterodimers, as well as the soluble DR4-beta chain alone. Furthermore, two out of twelve DR4-beta peptides could interact specifically with CD4. These findings show that CD4 interacts with a region of MHC class II molecules analogous to a previously identified loop in class I MHC proteins that binds CD8 (refs 8, 9).
Sllmm~Previous studies indicated that CD3-CD16 + natural killer (NK) cells are capable of specific alloantigen recognition. Thus, alloreactive NK clones lysed normal aUogeneic target cells (phytohemagglutinin [PHA] blasts) bearing the stimulating alloantigen but did not lyse autologous cells or the majority of unrelated allogeneic cells. In this study we investigated whether NK cells isolated from single individuals could exhibit different aUospecifcities. To this end, we derived large numbers of CD3-CD16 + clones (in the presence of PHA) from fresh CD3-peripheral blood lymphocytes. Cloning effciencies ranged between 5 and 10%. The resulting CD3-CD16 + clones were tested for their reactivity against a panel of allogeneic PHA blasts (derived from six donors). In a given individual (A), four distinct groups of clones could be identifed according to their pattern of reactivity (over 400 clones have been analyzed). Clones that could be assigned to one or another group of specificity represented 36% of all clones derived from this donor. The remaining clones did not display cytolytic activity against any of the aUogeneic target cells used in the panel. None of the clones lysed autologous (A) PHA blasts, yet, these cells were lysed by the representative clones G10 and H12 specific for donor A. Clones displaying a cytolytic pattern of reactivity identical to that defined for donor A were present in other individuals studied, however not all groups of allospecific clones were necessarily represented in different individuals. Allospecifc clones belonging to the various groups were homogeneous in the expression of EB6/GL183-triggering surface molecules, and could thus be assigned to one or another of the previously defined subsets of NK cells. Genetic analysis of the new NK-defined alloantigens was performed in representative families. The corresponding characters were found to segregate independently and, at least for three of them, an autosomic recessive type of inheritance could be demonstrated. Moreover, the comparative analysis of the segregation of the major histocompatibility complex haplotypes and the recessive or dominant alleles of the genes governing the five specificities analyzed indicated that there is no independent sampling between the two genetic traits, thus suggesting that the genes regulating the NK-defined specificities are carried by chromosome 6. Finally, some donors expressed more than one specificity, thus providing evidence for an NK-defined complex haplotype.
Background Toxicant associated fatty liver disease (TAFLD) is a recently identified form of non-alcoholic fatty liver disease (NAFLD) associated with exposure to industrial chemicals and environmental pollutants. Numerous studies have been conducted to test the association between industrial chemicals/ environmental pollutants and fatty liver disease both in vivo and in vitro. Objectives The objective of the paper is to report a list of chemicals associated with TAFLD. Methods Two federal databases of rodent toxicology studies– ToxRefDB (Environmental Protection Agency) and Chemical Effects in Biological Systems (CEBS, National Toxicology Program) were searched for liver endpoints. Combined, these two databases archive nearly 2000 rodent studies. TASH descriptors including fatty change, fatty necrosis, Oil red O positive staining, steatosis and lipid deposition were queried. Results Using these search terms, 123 chemicals associated with fatty liver were identified. Pesticides and solvents were the most frequently identified chemicals, while PCBs/dioxins were the most potent. About 44% of identified compounds were pesticides or their intermediates, and nearly 10% of pesticide registration studies in ToxRefDB were associated with fatty liver. Fungicides and herbicides were more frequently associated with fatty liver than insecticides. Conclusions More research on pesticides, solvents, metals and PCBs/dioxins in NAFLD/TAFLD is warranted due to their association with liver damage.
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