Inhibition of the allograft response by donor specific blood transfusion: association with reduced local TH1 cytokines and nitric oxide but enhanced prostaglandin E2 production

Eicosanoid-induced store-operated calcium entry in dendritic cells

BACKGROUND

Eicosanoids are generally recognized to exert potent immunomodulatory properties, including effects on T cell, antigen-presenting cell (APC), and dendritic cell (DC) maturation and function. Since DC maturation and function may also be regulated by store-operated calcium entry (SOCE), we hypothesized that the effects of eicosanoids on DC function may in part be regulated through changes in intracellular calcium.

METHODS

DC derived from the bone marrow of male Balb/ByJ mice cultured for 7 d in the presence of granulocyte macrophage colony stimulating factor (GM-CSF) and interleukin-4 (IL-4) were used to study the effects of eicosanoids on SOCE and the resulting Ca(2+) mobilization.

RESULTS

The 5-lipoxygenase (5-LO) products leukotriene B(4) (LTB(4)) and LTD(4,) but not LTC(4), depleted Ca(2+) from DC endoplasmic reticulum stores. The specificity of LTB(4) and LTD(4) on Ca(2+) store-depletion was confirmed by the ability of the specific receptor antagonists, LY25583 and MK571, respectively, to abrogate Ca(2+) store depletion. RT-PCR demonstrated DC receptors for LTB(4) (BLT(1) and BLT(2)) and the cysteinyl-LTs (CysLT(1), CysLT(2), and GPR17). We also detected transient receptor potential canonical (TRPC) 1, 2, 4, and 6 and stromal interaction molecule 1 (STIM1) on CD11c(+) DCs, suggesting these proteins also participate in DC SOCE. In contrast, the cyclooxygenase (CO) metabolite PGE(2) had no effect on DC Ca(2+) mobilization.

CONCLUSIONS

To our knowledge, these are the first observations of distinct effects of eicosanoids on DC Ca(2+) mobilization, which may have important implications for the regulation of DC maturation at sites of immune and non-immune inflammation.

Application of popliteal lymph node assay to evaluate tolerogenic effect of donor leukocyte infusion

BACKGROUND

Popliteal lymph node assay (PLNA) has long been proposed to detect immunostimulating potential of chemicals. Here, the PLNA was used to evaluate the effect of donor leukocyte infusion on recipients' reaction to donor-specific antigens.

METHODS

Donor rats' peripheral blood leukocytes (ranging from 1 x 10(4) to 500 x 10(4) cells) were intravenously (i.v.) infused into recipients. A week later recipients' reaction to donor-specific antigen was evaluated, using the PLNA technique, by subcutaneous injection of donor spleen cells to one hind footpad of recipients and injection of saline to the other. Seven days later all recipients were killed and their PLNs' weight and cellularity indices were determined. While the same process was applied to the positive control (PC) animals, rats without leukocyte infusion, negative control (NC) animals, rats without leukocyte infusion, were injected in both hind footpads with saline.

RESULTS

The PLN weight indices of recipients of: > or =5 x 10(4) leukocytes were significantly lower than PC animals (P < 0.001), whereas the weight indices of recipients of 1 x 10(4) cells were similar to PC group but higher than NC animals (P < 0.0001). However, the PLN cellularity indices of recipients of < or =10 x 10(4) cells were not different from PC animals but the PLN cellularity indices of recipients of: > or =50 x 10(4) cells were significantly lower than PC group (P < 0.05).

CONCLUSION

Overall, these results suggest that donor leukocytes infusion dose-dependently decrease reaction to donor-specific antigens, but a state of tolerance to donor antigen might be induced at the dose of: > or =50 x 10(4) cells. PLNA appears to represent a simple test model to quantify efficacy of immunotolerance protocols.

Is the CD200/CD200 receptor interaction more than just a myeloid cell inhibitory signal?

The membrane glycoprotein CD200, which has a widespread but defined distribution and a structurally similar receptor (CD200R) that transmits an inhibitory signal to cells of the hematopoetic lineage, especially myeloid cells, has been characterized. CD200R expression is restricted predominantly to cells of the myeloid lineage indicating that this ligand/receptor pair has a specific role in controlling myeloid cell function. In addition to CD200R, several related genes have been identified. Whether these gene products also regulate immune function is controversial. CD200R is also expressed by certain subsets of T cells and CD200 may be expressed by antigen-presenting cells, adding additional layers of complexity to the CD200/CD200R axis. Because monocytic myeloid cells provide a link between the innate and adaptive immune response, mechanisms to control their function through receptors such as CD200R will have therapeutic potential. Regulation of immune responses is accomplished by the concerted, but opposing, activity of kinases and phosphatases, fine control often being achieved through paired receptors. In this review, we will consider whether CD200R signaling functions within a framework of paired activating and inhibitory receptors and whether the inhibitory signal delivered has functional consequences beyond inhibition of myeloid cell proinflammatory activation.

Citrate shows specific, dose-dependent lympholytic activity in neoplastic cell lines

We have demonstrated cell membrane destruction activity by carboxylic acid derivatives (CADs) mainly tri-sodium citrate, in neoplastic cell lines and, to a far lesser extent, in normal human peripheral blood mononuclear cells (hPBMC). Flow cytometric (FACS) analysis was applied to Annexin-V and Propidium Iodide (PI) stained cells to evaluate the degree of the apoptosis induced by citrate in the following cell lines: CCRF-CEM (shortened to CEM), H9, and Jurkat (T-Cells), Raji and WIL2-NS (B-Cells), HL-60 (myeloblasts), K562 (myelocytes) and U937 (monocytes). We also tested normal hPBMC. Before staining with Annexin/PI, manual cell counts were performed on 24- and 48-h-old cell cultures. Cell supernatants were assayed for lactate dehydrogenase (LDH). LDH values in samples correlated with enhanced apoptosis by FACS analysis. For comparison, ascorbate and 2 other CADs including, acetate and lactate were also evaluated for the induction of apoptosis. In addition, the ability of tri-sodium citrate to induce apoptosis in the presence and the absence of several antineoplastic drugs, such as dexamethasone, arsenic trioxide, hydrocortisone, 6-mercaptopurine, and methotrexate were tested on Jurkat cells. FACS, LDH, and cell count values all demonstrated an enhanced degree of apoptotic cell death in Jurkat cells by citrate. In most of our investigated cells, except for the H9 cell line, citrate has induced a greater degree of apoptosis than acetate which induced a greater degree than lactate (see Fig. 1.0). The nature of the cell death by ascorbate appeared to be due to necrosis rather than apoptosis. Pilot studies on normal hPBMC showed that citrate alone or in combination with antineoplastic drugs caused minimal cell death. Thus citrate might be of benefit in some chemotherapy treatments in order to reduce drug toxicity or possibly enhance drug activities in certain neoplasias.

IgG antiplatelet immunity is dependent on an early innate natural killer cell–derived interferon-γ response that is regulated by CD8+ T cells

The mechanisms responsible for immunoglobulin G (IgG) immunity against allogeneic platelets are poorly understood. We studied the role that murine recipient CD8+ T and natural killer (NK) cells play in immunity against allogeneic platelets. BALB/c mice were depleted of the cells by cell-specific antibodies, transfused weekly with platelets from C57BL/6 mice, and serum IgG antidonor antibodies were measured by flow cytometry. While allogeneic platelet transfusions into wild-type recipients stimulated IgG antidonor antibodies in all mice by the fifth transfusion, CD8-depleted mice had significantly (P &lt; .001) enhanced antibody production. Isotype analysis revealed that CD8+ T cells suppressed T-helper 2 (Th2)-associated IgG1 but enhanced Th1-associated IgG2a. Compared with wild-type mice, platelet transfusions into CD8-depleted mice stimulated enhanced intracellular interferon (IFN)-γ production by CD4- lymphocytes within 24 hours after the first transfusion. The early IFN-γ response correlated with nitric oxide-dependent splenic cytotoxicity (P &lt; .001). In asialo ganglioside monosialic acid 1 (GM1)-depleted mice transfused with allogeneic platelets, the IFN-γ production, splenic cytotoxicity, and IgG antidonor antibody response were significantly suppressed. These results demonstrate that IgG antiplatelet immunity is dependent on an early NK cell-derived IFN-γ response that is negatively regulated by CD8+ T cells and suggest that targeting innate NK cell responses may significantly reduce platelet alloimmunization. (Blood. 2004;103:2705-2709)

Fatty acids, the immune response, and autoimmunity: a question of n-6 essentiality and the balance between n-6 and n-3

The essentiality of n-6 polyunsaturated fatty acids (PUFA) is described in relation to a thymus/thymocyte accretion of arachidonic acid (20:4n-6, AA) in early development, and the high requirement of lymphoid and other cells of the immune system for AA and linoleic acid (1 8:2n-6, LA) for membrane phospholipids. Low n-6 PUFA intakes enhance whereas high intakes decrease certain immune functions. Evidence from in vitro and in vivo studies for a role of AA metabolites in immune cell development and functions shows that they can limit or regulate cellular immune reactions and can induce deviation toward a T helper (Th)2-like immune response. In contrast to the effects of the oxidative metabolites of AA, the longer-chain n-6 PUFA produced by gamma-linolenic acid (18:3n-6, GLA) feeding decreases the Th2 cytokine and immunoglobulin (Ig)G1 antibody response. The n-6 PUFA, GLA, dihomo-gamma-linolenic acid (20:3n-6, DHLA) and AA, and certain oxidative metabolites of AA can also induce T-regulatory cell activity, e.g., transforming growth factor (TGF)-beta-producing T cells; GLA feeding studies also demonstrate reduced proinflammatory interleukin (IL)-1 and tumor necrosis factor (TNF)-alpha production. Low intakes of long-chain n-3 fatty acids (fish oils) enhance certain immune functions, whereas high intakes are inhibitory on a wide range of functions, e.g., antigen presentation, adhesion molecule expression, Th1 and Th2 responses, proinflammatory cytokine and eicosanoid production, and they induce lymphocyte apoptosis. Vitamin E has a demonstrable critical role in long-chain n-3 PUFA interactions with immune functions, often reversing the effects of fish oil. The effect of dietary fatty acids on animal autoimmune disease models depends on both the autoimmune model and the amount and type of fatty acids fed. Diets low in fat, essential fatty acid deficient (EFAD), or high in long-chain n-3 PUFA from fish oils increase survival and reduce disease severity in spontaneous autoantibody-mediated disease, whereas high-fat LA-rich diets increase disease severity. In experimentally induced T cell-mediated autoimmune disease, EFAD diets or diets supplemented with long-chain n-3 PUFA augment disease, whereas n-6 PUFA prevent or reduce the severity. In contrast, in both T cell- and antibody-mediated autoimmune disease, the desaturated/elongated metabolites of LA are protective. PUFA of both the n-6 and n-3 families are clinically useful in human autoimmune-inflammatory disorders, but the precise mechanisms by which these fatty acids exert their clinical effects are not well understood. Finally, the view that all n-6 PUFA are proinflammatory requires revision, in part, and their essential regulatory and developmental role in the immune system warrants appreciation.

Prostaglandin E(2) inhibits IL-18-induced ICAM-1 and B7.2 expression through EP2/EP4 receptors in human peripheral blood mononuclear cells

Costimulatory molecules play important roles in immune responses. In the present study we investigated the effects of PGE(2) on the expression of ICAM-1, B7.1, and B7.2 on monocytes in IL-18-stimulated PBMC using FACS analysis. Addition of PGE(2) to PBMC inhibited ICAM-1 and B7.2 expression elicited by IL-18 in a concentration-dependent manner. We examined the involvement of four subtypes of PGE(2) receptors, EP1, EP2, EP3, and EP4, in the modulatory effect of PGE(2) on ICAM-1 and B7.2 expression elicited by IL-18, using subtype-specific agonists. ONO-AE1-259-01 (EP2R agonist) inhibited IL-18-elicited ICAM-1 and B7.2 expression in a concentration-dependent manner with a potency slightly less than that of PGE(2), while ONO-AE1-329 (EP4R agonist) was much less potent than PGE(2). The EP2/EP4R agonist 11-deoxy-PGE(1) mimicked the effect of PGE(2) with the same potency. ONO-D1-004 (EP1R agonist) and ONO-AE-248 (EP3R agonist) showed no effect on IL-18-elicited ICAM-1 or B7.2 expression. These results indicated that EP2 and EP4Rs were involved in the action of PGE(2). Dibutyryl cAMP and forskolin down-regulated ICAM-1 and B7.2 expression in IL-18-stimulated monocytes. As EP2 and EP4Rs are coupled to adenylate cyclase, we suggest that PGE(2) down-regulates IL-18-induced ICAM-1 and B7.2 expression in monocytes via EP2 and EP4Rs by cAMP-dependent signaling pathways. The fact that anti-B7.2 as well as anti-ICAM-1 Ab inhibited IL-18-induced cytokine production implies that PGE(2) may modulate the immune response through regulation of the expression of particular adhesion molecules on monocytes via EP2 and EP4Rs.