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The immune system has been shown to be involved in not only the host defense against infectious pathogens but also in tissue repair processes continuously occurring in the body. Our review presents the hypothesis about the mechanism of TLR-mediated regulation of adaptive immune responses linked to the tissue destruction. In our opinion following injury to a tissue, the expression of tissue-specific determinant/MHC class II complexes on dendritic cells and macrophages are upregulated significantly due to the increased uptake of tissue debris. Consequently, T-cells become activated as a result of low affinity, but high avidity interactions between self-reactive CD4+T cells and antigen-presenting cells (APCs). The type of self antigen-induced immune responses depends on the multiple downstream signals generated by intracellular toll-like receptors (TLRs) 3, 7, 8, and 9, that discriminate "self" and "non-self" nucleic acids. Accumulating data suggest that ligation of intracellular TLRs by endogenous DNA/RNA released from necrotic cells may result in developing Th2-like responses, as well as in the alternative activation of macrophages (M2), that favor local tissue protection and compensatory cell growth. In contrast, ligation of intracellular TLRs by exogenous pathogen-derived DNA/RNA may promote Th1-driven responses, as well as classical activation of macrophages (M1), that contribute to local tissue destruction and suppress cell growth. We suggest here that the balance between the host- and pathogen-derived nucleic acids interacting with intracellular TLRs contributes to the balance between immune-mediated tissue-protective and tissue-destructive events occurring in the body., (Copyright © 2011 Elsevier GmbH. All rights reserved.)

Nucleated erythroid cells (NEC) have been previously reported to the capable of suppressing antibody-mediated primary (IgM) and secondary (IgG) immune responses to thymus-dependent antigens. In the present study we indicated that NEC, separated from the spleens of mice following phenylhydrazine treatment were able to suppress directly the proliferative response of preactivated B cells to lipopolysaccharide (LPS) in vitro. While being active in suppressing B cell blastogenesis, NEC, however, failed to reduce both cell proliferation and cytotoxic T lymphocyte (CTL) generation in an allogeneic mixed lymphocyte culture (MLC). NEC also lacked a significant effect on interleukin (IL)-2 production and utilization by concanavalin A (Con A)-activated T lymphocytes. The NEC-derived suppression of B cell proliferation was, at least in part, mediated by soluble molecules. The specific blockade of transforming growth factor (TGF)-beta synthesis with antisense oligodeoxynucleotides (OD) binding TGF-beta mRNA, as well as the neutralization of TGF-beta activity with anti-TGF-beta antibodies (Ab), resulted in a detectable diminished ability of the NEC-conditioned medium (CM) to suppress B cell blastogenesis. Taken together, the results suggest that: 1) NEC may suppress directly B cell responses, while not affecting T cell ones; 2) NEC may mediate their natural suppressor (NS) activity partially through releasing TGF-beta.

When normal murine bone marrow (BM) cells were cultured with either L1210 lymphoma cells or P815 mastocytoma cells for 24 h, considerable tumor growth suppression without substantial tumor cell lysis was found. Under the same conditions, normal spleen cells also demonstrated the antitumor cytostatic activity, but not as significant as that characteristic of BM cells, whereas both normal thymus and lymph node cells had not any suppressive effect on tumor cell proliferation. The comparable cytostatic effects occurred in both syngeneic and allogeneic BM-tumor cell combinations. The cytostatic BM-effectors were distinct from T and B lymphocytes or mature macrophages. After being separated on a discontinuous Percoll density gradient, the cells active in suppressing tumor growth were recovered predominantly in 1.075 and 1.060 density fractions. The cytostatic BM effectors, at least in their part, were resistant to x-irradiation up to 2000 rad included. Collectively these results suggest that normal BM, being deficient in cell-mediated antitumor cytolytic activity, has a significant leukemia growth inhibitory potential; and that cytostatic BM effectors are similar in their characteristics to natural suppressor cells.