TLR4/MyD88-induced CD11b+Gr-1 int F4/80+ non-migratory myeloid cells suppress Th2 effector function in the lung.

In humans, environmental exposure to a high dose of lipopolysaccharide (LPS) protects from allergic asthma, the immunological underpinnings of which are not well understood. In mice, exposure to a high LPS dose blunted house dust mite-induced airway eosinophilia and T-helper 2 (Th2) cytokine production. Although adoptively transferred Th2 cells induced allergic airway inflammation in control mice, they were unable to do so in LPS-exposed mice. LPS promoted the development of a CD11b(+)Gr1(int)F4/80(+) lung-resident cell resembling myeloid-derived suppressor cells in a Toll-like receptor 4 and myeloid differentiation factor 88 (MyD88)-dependent manner that suppressed lung dendritic cell (DC)-mediated reactivation of primed Th2 cells. LPS effects switched from suppressive to stimulatory in MyD88(-/-) mice. Suppression of Th2 effector function was reversed by anti-interleukin-10 (IL-10) or inhibition of arginase 1. Lineage(neg) bone marrow progenitor cells could be induced by LPS to develop into CD11b(+)Gr1(int)F4/80(+)cells both in vivo and in vitro that when adoptively transferred suppressed allergen-induced airway inflammation in recipient mice. These data suggest that CD11b(+)Gr1(int)F4/80(+) cells contribute to the protective effects of LPS in allergic asthma by tempering Th2 effector function in the tissue.

Distinct autoreactive T cell responses to native and fragmented DNA topoisomerase I: influence of APC type and IL-2.

Systemic sclerosis (SSc) is an autoimmune connective tissue disease of unknown etiology in which T cell responses to various autoantigens, including DNA topoisomerase I (Topo I), have been implicated. We investigated whether dendritic cells, generally considered to be the most potent APCs for the initiation of immune responses, would present either of two forms of Topo I to T cells more efficiently than PBMC APCS: Using cells from healthy controls and SSc patients, several important observations were made. First, neither APC type was able to initiate T cell proliferative responses to full-length native Topo I unless exogenous IL-2 was added. This is in contrast to vigorous T cell proliferation in response to Topo I polypeptide fragments presented by either APC type. Second, T cell responses to the full-length form of Topo I presented by dendritic cells were considerably lower than responses to Ag presented by PBMC APCS: Finally, no secondary T cell responses were observed unless the same Ag/APC combination as that used in the primary stimulation was maintained. These data indicate that different peptides are generated based upon the form of the Topo I and the APC that processes it. Taken together, these results suggest that a very specific combination of antigenic form and APC may be involved in breaking tolerance to Topo I in the early stages of development of SSC:

Generation of DC from mouse spleen cell cultures in response to GM-CSF: immunophenotypic and functional analyses.

In all tissues that have been studied to date, dendritic leucocytes constitute only a small proportion of total cells and are difficult both to isolate and purify. This study reports on a method for the propagation of large numbers of dendritic cells (DC) from mouse spleen using granulocyte-macrophage colony-stimulating factor (GM-CSF) and their characteristics. Within a few days of liquid culture in GM-CSF, B10 BR (H-2k, I-E+) mouse splenocytes formed loosely adherent myeloid cell clusters. Mononuclear progeny released from these clusters at and beyond 4 days exhibited distinct dendritic morphology and strongly expressed leucocyte common antigen (CD45), CD11b, heat-stable antigen, Pgp-1 (CD44) and intercellular adhesion molecule-1 (ICAM-1; CD54). The intensity of expression of the DC-restricted markers NLDC 145 and 33D1, the macrophage marker F4/80, and Fc gamma RII (CDw32) was low to moderate, whereas the cells were negative for CD3, CD45RA and NK1.1. High and moderate levels, respectively, of cell surface staining for major histocompatibility complex (MHC) class II (I-Ek) and the B7 antigens (counter-receptors of CTLA4, a structural homologue of CD28) were associated with potent stimulation of unprimed, allogeneic T cells (B10; H-2b, I-E-). DC propagated in a similar fashion from DBA/2 mouse spleen proved to be strong antigen-presenting cells (APC) for MHC-restricted, syngeneic T-helper type 2 (Th2) cell clones specifically responsive to sperm whale myoglobin. Footpad or intravenous injection of GM-CSF-stimulated B10.BR spleen-derived DC into B10 (H-2b, I-E-) recipients resulted in homing of the allogeneic cells to T-cell-dependent areas of lymph nodes and spleen, where they strongly expressed donor MHC class II antigen 1-2 days later. These findings indicate that cells can be propagated from fresh splenocyte suspensions that exhibit distinctive features of DC, namely morphology, motility, cell-surface phenotype, potent allogeneic and syngeneic APC function and in vivo homing ability. Propagation of DC in this manner from progenitors present in lymphoid tissue provides an alternative and relatively convenient source of high numbers of these otherwise difficult to isolate but functionally important APC.