Accessory cell dependent T lymphocyte proliferation: potent activity of dendritic cells

Restoration of abated T cell stimulation activity of mature dendritic cells

Freshly isolated and cultured mature dendritic cells (DC) rapidly lose their high capacity to activate T cells. This diminished T cell activation activity is due, in part, to dramatically reduced expression of the costimulation ligands B7-1 (CD80) and B7-2 (CD86). Here we show that cultivation of mature DC with the lymphokines TNFalpha, GM-CSF, or TNFalpha plus GM-CSF, fully restored and enhanced their T-cell stimulation activity by two to threefold, four to fivefold, or six to sevenfold, respectively. The restored T-cell stimulation activity was directly correlated with induced and increased levels of CD80 (16-fold) and CD86 (10-fold) expression by the lymphokine-cultured DC. These results should facilitate many current DC-vaccination efforts towards generating more potent T cell responses.

Effects of interferons beta or gamma on neopterin biosynthesis and tryptophan degradation by human alveolar macrophages in vitro: synergy with lipopolysaccharide

Interferons can induce neopterin biosynthesis and tryptophan degradation in monocytic cells. Indoleamine 2,3-dioxygenase (IDO), an inducible cellular enzyme, metabolizes tryptophan to N-formyl-L-kynurenine. Tryptophan degradation has been linked to interferon-mediated inhibition of replication by intracellular pathogens and inhibition of cancer cell proliferation. We evaluated the ability of the recombinant human interferons beta ser and gamma to stimulate neopterin production and tryptophan degradation in vitro by alveolar macrophages (AM) obtained from normal volunteers by bronchoalveolar lavage. Additionally, because other biologic response modifiers such as lipopolysaccharide (LPS) can also stimulate monocytic cells to produce increased amounts of neopterin and degrade tryptophan, we evaluated the effects of LPS on interferon-induced neopterin production and tryptophan degradation by AM. Both interferon-gamma (IFN-gamma) and interferon-beta (IFN-beta) induced neopterin production and tryptophan degradation by AM with corresponding inhibition of intracellular replication by Chlamydia psittaci in AM, but IFN-gamma was a more potent inducer of these responses than IFN-beta. LPS enhanced neopterin production and tryptophan degradation by interferon-exposed cells. This effect was particularly evident at lower concentrations of interferon, and LPS synergy was more pronounced with IFN-beta than IFN-gamma. Concentrations of LPS that alone had no stimulatory effect on tryptophan degradation synergistically enhanced the induction of IDO activity by lower concentrations of interferon. These studies suggest that IFN-gamma stimulates human AM to produce neopterin and degrade tryptophan more potently than IFN-beta, and that low concentrations of LPS can synergistically enhance such effects of interferons on tissue macrophage metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Omental dendritic cells: Ia expression and relation to macrophages

Rat omental dendritic cells (ODC) occur in two forms, mainly spindle-shaped, Ia-, on the surface, and stellar, Ia+ within the omentum. Like macrophages, most ODC label with W3/25 mAb and have a demonstrable activity of non-specific esterase, acid phosphatase and ATPase. Up to 30% of ODC are actively phagocytic. The proportion of Ia+ ODC rises 7 days after ip antigenic stimulation and there seems to be a reciprocal development of Ia positivity and phagocytic capacity between ODC and macrophages 3 and 5 days after ip immunization. ODC contribute to the overall fluctuation of Ia expression in the entire omentum after immunization. Ia+ ODC display a linear arrangement along preilymphatic spaces and may be related to the formation of new lymph vessels. They also constitute the stroma of pseudofollicles containing clusters of what are presumably T-helper lymphocytes closely attached to ODC, scattered suppressor T lymphocytes and B cells accumulating in later stages at the immune response.

Conditioned medium from activated rat macrophages and the recombinant factors, IL-1 beta and GM-CSF, enhance the accessory activity of dendritic cells

Low density lymph node cells (LD-LNC; 5% of total unfractionated LNC) contain 95% of the accessory activity required for responses of T lymphocytes to mitogens. Significantly greater responses to mitogens occur when T lymphocytes are added to LD-LNC that have been exposed overnight to silica, in comparison to responses occurring with LD-LNC incubated without silica. Conditioned medium (CM) from silica-treated LD-LNC is itself able to mediate enhanced responses; i.e., when LD-LNC are exposed overnight to CM alone and mitogen-treated T lymphocytes added the next day. The enhancing activity found in CM from LD-LNC exposed to silica is produced by macrophages; however, their low accessory activity is not enhanced by CM. In contrast, dendritic cells isolated from LD-LNC exposed to silica or to CM show significantly increased accessory activity, but dendritic cells do not produce the enhancing activity found in CM. CM lacks IL-2 activity and does not have any effect on the responses of untreated or mitogen-treated T lymphocytes alone. Thus, macrophages produce the enhancing activity and dendritic cells respond to it. Maximum enhancement of dendritic cell accessory activity requires overnight exposure to CM; once induced, accessory activity is not further modulated after continued incubation in the presence or absence of CM. LD-LNC, adherent peritoneal exudate cells, and adherent thioglycollate-induced peritoneal exudate cells produce enhancing activity after exposure to silica, LPS, and silica plus LPS. After gel filtration of a CM produced by silica plus LPS, enhancing activity shows a broad molecular weight distribution between 20 and 55 kD. IL-1 is present in CM and shows a more narrow molecular weight distribution that falls within the lower molecular weight range for enhancing activity. Silica treatment by itself produces CM containing little IL-1, but abundant enhancing activity; gel filtration of this CM shows that the distribution of enhancing activity is confined more narrowly to the higher molecular weight range, suggesting that IL-1 is one of several factors that enhances the accessory activity of dendritic cells. Recombinant human IL-1 beta does have enhancing activity, but of the other recombinant factors tested only mouse GM-CSF also has enhancing activity. Human IL-1 alpha, tumor necrosis factor alpha, IL-4, rat IL-3 and rat IFN-gamma, as well as L cell-conditioned medium containing M-CSF, lack enhancing activity.

The effect of silica treatment on accessory cell-dependent rat T lymphocyte proliferation

Previous work has shown that purified rat macrophages lack both accessory activity for T lymphocyte responses to mitogens and stimulatory activity in a mixed leukocyte reaction, in marked contrast to the potent activity of dendritic cells. This study was designed to re-evaluate macrophages as accessory cells by treating various cell preparations with either silica or L-leucine methyl ester, which have been reported to be toxic to macrophages, and then determining the effect of the treated cells on responses to the mitogens, sodium periodate or concanavalin A. These studies indicated that treatment with L-leucine methyl ester failed to kill rat macrophages or dendritic cells, whereas silica was specifically toxic for rat macrophages. The studies therefore focused on silica. Co-culturing mitogen-treated lymph node cells with silica over a wide range of concentrations had no effect on responses. The same results were obtained if mitogen-treated lymphocytes were enriched with lymph node macrophages and dendritic cells and then co-cultured with silica. Preparations containing both macrophages and dendritic cells were incubated with silica for 24 h to ensure the death of virtually all macrophages; upon the addition of mitogen-treated lymphocytes, the macrophage-depleted accessory cells induced vigorous proliferative responses. Peritoneal exudate cells showed variable, but low accessory activity that increased after incubation with silica. Elimination of more than 90% of the macrophages from peritoneal exudate cells, as determined by staining for non-specific esterase, failed to eliminate this accessory activity. Taken together, these findings confirm and extend the conclusion that rat macrophages lack or have exceedingly low accessory activity.