A multidonor ELISPOT study of IL-1 beta, IL-2, IL-4, IL-6, IL-13, IFN-gamma and TNF-alpha release by cryopreserved human peripheral blood mononuclear cells

The tumor immune-microenvironment in gastric cancer

AIMS AND BACKGROUND

The tumor microenvironment significantly influences malignant behavior and progression. Many components are involved in the tumor microenvironment, including extracellular matrix, stromal cells, immune and inflammatory cells, as well as cytokines that promote tumor development with complex interactions through the exchange of molecular information. It is now known that tumor immune escape may be influenced by the tumor microenvironment. The aim of this work is to conduct a review of the tumor immune-microenvironment in gastric cancer.

METHODS

We review the current knowledge of several immune cells involved in the gastric tumor microenvironment. In addition, a brief description of immunotherapy strategies for gastric cancer is also reviewed.

CONCLUSIONS

Among immune cell populations, lymphocytes, macrophages, dendritic cells and myeloid-derived suppressor cells are revealed to make the difference in promoting or suppressing gastric tumorigenesis, either directly or indirectly, via regulating the immune responses. Understanding these interactions in detail within the tumor immune-microenvironment will contribute to unraveling new therapeutic targets.

Progesterone Modulation of Pregnancy-Related Immune Responses

Progesterone (P4) is an important steroid hormone for the establishment and maintenance of pregnancy and its functional withdrawal in reproductive tissue is linked with the onset of parturition. However, the effects of P4 on adaptive immune responses are poorly understood. In this study, we took a novel approach by comparing the effects of P4 supplementation longitudinally, with treatment using a P4 antagonist mifepristone (RU486) in mid-trimester pregnancies. Thus, we were able to demonstrate the immune-modulatory functions of P4. We show that, in pregnancy, the immune system is increasingly activated (CD38, CCR6) with greater antigen-specific cytotoxic T cell responses (granzyme B). Simultaneously, pregnancy promotes a tolerant immune environment (IL-10 and regulatory-T cells) that gradually reverses prior to the onset of labor. P4 suppresses and RU486 enhances antigen-specific CD4 and CD8 T cell inflammatory cytokine (IFN-γ) and cytotoxic molecule release (granzyme B). P4 and RU486 effectively modulate immune cell-mediated interactions, by regulating differentiated memory T cell subset sensitivity to antigen stimulation. Our results indicate that P4 and RU486, as immune modulators, share a reciprocal relationship. These data unveil key contributions of P4 to the modulation of the maternal immune system and suggests targets for future modulation of maternal immune function during pregnancy.

Membrane Microplates for One- and Two-Color ELISPOT and FLUOROSPOT Assays

Membranes are widely used as protein blotting matrices for a large variety of research applications including western blotting and enzyme-linked immunospot assay (ELISPOT). The largest advantage of using membranes versus solid plastic support is the porosity of membranes allowing for immobilization of high concentrations of proteins and antibodies which, in turn, increases the sensitivity of detection. Similar to plastic surfaces, polyvinylidene difluoride (PVDF) and nitrocellulose membranes create good microenvironment for live cells cultured in vitro and do not interfere with cellular physiology. It appears that PVDF-backed microplates are a golden standard for ELISPOT assays: such plates are inexpensive, easy to use and after assay development, membranes can be removed from the plates and archived. Given the convenience and reliability of membrane microplates, they are widely used in ELISPOT assays for basic research and clinical trials. The ELISPOT assay is an antibody "sandwich" technique aimed at trapping cell-secreted molecules between capture and detection antibodies, followed by either chromogenic enzymatic or fluorescence detection. This review covers the principles of the ELISPOT assay on membrane microplates including single-color and two-color detection techniques with the emphasis on assay design, choosing membrane microplates, and troubleshooting protocols.

Comparative Multi-Donor Study of IFNγ Secretion and Expression by Human PBMCs Using ELISPOT Side-by-Side with ELISA and Flow Cytometry Assays

ELISPOT, ELISA and flow cytometry techniques are often used to study the function of immune system cells. It is tempting to speculate that these assays can be used interchangeably, providing similar information about the cytokine secreting activity of cells: the higher the number of cytokine-positive cells measured by flow cytometry, the higher the number of cytokine-secreting cells expected to be detected by ELISPOT and the larger the amount of secreted cytokine expected to be measured by ELISA. We have analyzed the expression level and secretion capacity of IFNγ from peripheral blood mononuclear cells isolated from five healthy donors and stimulated by calcium ionomycin mixed with phorbol 12-myristate 13-acetate in a non-specific manner in side-by-side testing using ELISPOT, ELISA and flow cytometry assays. In our study, we observed a general correlation in donors' ranking between ELISPOT and flow cytometry; ELISA values did not correlate with either ELISPOT or flow cytometry. However, a detailed donor-to-donor comparison between ELISPOT and flow cytometry revealed significant discrepancies: donors who have similar numbers of IFNγ-positive cells measured by flow cytometry show 2-3-fold differences in the number of spot-forming cells (SFCs) measured by ELISPOT; and donors who have the same number of SFCs measured by ELISPOT show 30% differences in the number of IFNγ-positive cells measured by flow cytometry. Significant discrepancies between donors were also found when comparing ELISA and ELISPOT techniques: donors who secreted the same amount of IFNγ measured by ELISA show six-fold differences in the number of SFCs measured by ELISPOT; and donors who have 5-7-times less secreted IFNγ measured by ELISA show a two-fold increase in the number of SFCs measured by ELISPOT compared to donors who show a more profound secretion of IFNγ measured by ELISA. The results of our study suggest that there can be a lack of correlation between IFNγ values measured by ELISPOT, ELISA and flow cytometry. The higher number of cytokine-positive cells determined by flow cytometry is not necessarily indicative of a higher number of cytokine-secreting cells when they are analyzed by either ELISPOT or ELISA. Our ELISPOT vs. ELISA comparison demonstrates that the higher number of SFCs observed in ELISPOT does not guarantee that these cells secrete larger amounts of cytokines compared to donors with lower SFC numbers. In addition, our data indicate that ELISPOT, ELISA and flow cytometry should be performed as complementary, rather than stand-alone assays: running these assays in parallel on samples from the same donors may help to better understand the mechanisms underlying the physiology of cytokine-secreting cells.

ELISPOT assay as a tool to study oxidative stress in lymphocytes

Enzyme-linked immuno spot (ELISPOT) assay is widely used for vaccine development, cancer and AIDS research, and autoimmune disease studies. The output of ELISPOT assay is a formation of colored spots which appear at the sites of cells releasing cytokines, with each individual spot representing a single cytokine-releasing cell. We worked out a protocol to study oxidative stress in human peripheral blood lymphocytes by determining their potency to secrete IFN-gamma, IL-2, IL-4, IL-5, IL-8, and TNF-alpha in response to acute treatment with hydrogen peroxide. We show that hydrogen peroxide-induced oxidative stress can cause a ∼twofold decrease in the number of lymphocytes secreting the TH1 cytokines IFN-gamma and IL-2, as well as chemokines IL-8 and TNF-alpha. However, the number of cells secreting TH2 cytokines IL-4 and IL-5 in hydrogen -peroxide-treated group did not change. It appears that oxidative stress may affect TH1-TH2 cytokine secretion -balance which, in turn, may underlie developments of various pathological conditions. This protocol can be easily modified to study the effects of many other oxidative stress compounds.

ELISpot assay as a tool to study oxidative stress in peripheral blood mononuclear cells

Enzyme-Linked Immuno Spot (ELISpot) assay is widely used for vaccine development, cancer and AIDS research, and autoimmune disease studies. The output of an ELISpot assay is a formation of colored spots which appear at the sites of cells releasing cytokines, with each individual spot representing a single cytokine-releasing cell.We have shown that hydrogen peroxide-induced oxidative stress was causing ∼twofold decrease in the number of lymphocytes secreting the TH1 cytokines IFN-gamma and IL-2, as well as chemokine IL-8 and cytokine TNF alpha. However, the number of cells secreting TH2 cytokines IL-4 and IL-5 in hydrogen peroxide-treated group did not change. Our ELISpot data indicate that oxidative stress may affect TH1-TH2 cytokine secretion balance which, in turn, may underlie developments of various pathological conditions. We adopted ELISpot assay for studying oxidative stress in human peripheral blood lymphocytes by analyzing the acute effect of hydrogen peroxide treatment on the frequency of cells secreting IFN-gamma, IL-2, IL-4, IL-5, IL-8, and TNF-alpha.

Effect of cryopreservation on IL-4, IFNgamma and IL-6 production of porcine peripheral blood lymphocytes

Cryopreservation of animal or human peripheral blood mononuclear cells (PBMC) is a commonly used technique. Effects of cryopreservation on functional capacity, especially the cytokine production of human PBMCs, have been extensively defined. However, certain animals, such as livestock, are a shortage of these information. Here we investigated the effects of cryopreservation on cytokine (IL-4, IFNgamma and IL-6) production of porcine PBMC. The porcine PBMCs were cryopreserved at -196 degrees C for a variety time periods for 2, 5, 25 and 50 days. Viability and cytokine production of the porcine PBMCs were measured before and after cryopreservation. The results showed that about 90% cell recovery rate was obtained at each storage time, indicating that about 10% loss of PBMCs in this short-term cryopreservation was due to the freezing process rather than the duration of cryopreservation. The fresh or frozen resting porcine PBMCs produced little cytokines in the absence of stimulation. However, three cytokines were apparently increased after PMA stimulation in both fresh and frozen porcine PBMCs. The sensitivity of frozen cells to PMA simulation for IFNgamma and IL-6 production was different from that of the fresh ones. IFNgamma production from the frozen PBMCs was significantly higher than that from the fresh ones (P<0.01). In contrast, IL-6 level from the frozen sample was significantly lower than that from the fresh one (P<0.05). Those results indicate that cryopreservation can increase the sensitivity of porcine PBMCs stimulated by PMA for IFNgamma production but not for IL-6 production. There was no significant difference of IL-4 production between fresh and frozen cells either stimulated (P>0.05) or un-stimulated (P>0.05).

ELISPOT assay on membrane microplates

Membranes used for western blotting can be also used for ELISPOT, an enzyme-linked immunospot assay, which allows determining frequencies of cytokine-secreting immune system cells. In addition to their high antibody-retaining capacity PVDF and NC membranes provide good support to immune system cells cultured in vitro and do not affect their physiology. ELISPOT assays utilizing membrane-backed microplates are used in many areas of research including vaccine development, HIV research, cancer and infection disease research, autoimmune disease, and allergy research.ELISPOT utilizes the same antibody "sandwich" technique as enzyme-linked immunosorbent assay, but unlike the latter ELISPOT belongs to state-of-the-art techniques when outcome of the assay depends on skills and accuracy of the operator, a thorough selection of matched pairs of capture and detection antibodies, and using appropriate staining reagents. This review covers basics of ELISPOT assay including its immunochemical design, selection of reagents and membrane microplates, and some troubleshooting recommendations.

Establishing acceptance criteria for cell-mediated-immunity assays using frozen peripheral blood mononuclear cells stored under optimal and suboptimal conditions

The enzyme-linked immunospot (ELISPOT) assay is a powerful tool for measuring antigen-specific cellular immune responses. The ability to use frozen peripheral blood mononuclear cells (PBMC) facilitates testing samples in multicenter clinical trials; however, unreliable ELISPOT responses may result if samples are not handled properly. Exposure of frozen PBMC to suboptimal storage temperature (-20 degrees C) or repeated cycling between more optimal storage temperatures (less than -130 degrees C and -70 degrees C) reduced the quality of frozen PBMC, as assessed by cell viability and functional ELISPOT response measures. Cell viability as assessed by trypan blue dye exclusion was reduced, and the percentage of apoptotic cells, as determined by the Guava Nexin assay, was significantly increased after these events. The functional gamma interferon ELISPOT responses to phytohemagglutinin (PHA) mitogen, a CD4 T-cell-specific antigen (varicella-zoster virus), and a CD8 T-cell-specific antigen (pool containing known cytomegalovirus, Epstein-Barr virus, and influenza virus peptides) were all significantly reduced after suboptimal storage events. However, for a given suboptimal storage event, the magnitude of the reduction varied between individuals and even among aliquots within an individual bleed, indicating the need for sample-specific acceptance criteria (AC). The percent viable or percent apoptotic cells after thaw, as well as the functional ELISPOT response to PHA, were all effective when applied with limits as AC for separating samples damaged during storage from valid control samples. Although all three AC measures could be effectively applied, the apoptosis AC limit applied was best for separating samples that could respond to antigenic stimulation from samples that could not effectively respond.

H-2 Kd-restricted hepatitis B virus-derived epitope whose specific CD8+ T lymphocytes can produce gamma interferon without cytotoxicity

It is necessary to evaluate the cytokine secretion status of CD8+ T lymphocytes and elucidate the factors influencing cytokine secretion, because the secretion of cytokines is also an important feature of CD8+ T lymphocytes, and the cytokines usually play critical roles in the outcome of diseases. We showed here that peptide AYRPPNAPI, derived from the core antigen of hepatitis B virus (HBV), could bind to H-2 Kd and induce primed splenocytes from HBcAg expression plasmid-immunized mice to produce gamma interferon (IFN-gamma) in H-2 Kd- and CD8-dependent manners instead of in a CD4-dependent manner. The induced cells were mainly CD3 and CD8 positive but had no cytotoxic effect on the corresponding target cells. When administered into HBV transgenic mice, these cells can decrease the serum HBV load without causing liver damage. These results suggest that this peptide is a special kind of CD8+ T-cell epitope, for which specific CD8+ T cells can produce IFN-gamma when antigenic stimulation is encountered but which have no cytotoxic effect on the corresponding target cells both in vitro and in HBV transgenic mice. This phenomenon indicates initially that the functional mechanisms of CD8+ T cells can be determined by their epitope specificity, which may be associated with the development of epitope-based immunotherapeutic approaches for infectious diseases and tumors.

Effect of cryopreservation on expression of Th1 and Th2 cytokines in blood mononuclear cells from patients with different cytokine profiles, analysed with three common assays: an overall decrease of interleukin-4

Studies on cytokine expression in blood cells are commonly performed on cryopreserved cells. Previous studies show that cryopreservation affects cytokine expression, but the findings are not consistent. This may be due to divergent effects of freezing on different cytokines, different stimuli, and different patient groups or to the use of different assays in the studies. This study was designed to investigate the effect of freezing on spontaneous, auto-antigen, allergen, and mitogen induced cytokine secretion from peripheral blood mononuclear cells from several groups of patients expressing different cytokine profiles; multiple sclerosis, atopic children, non-atopic children, and pregnant women. The expression of IFN-gamma, IL-4, IL-5, IL-9, IL-10, and IL-13 was analysed with ELISA, ELISPOT and/or real time RT-PCR. Our data provide evidence that the process of cryopreservation and thawing does affect the expression of cytokines, both at the protein and the mRNA level. Moreover, the effect varied among different cytokines, different stimuli, and different patient groups, which partly may be explained by differences in optimal freezing conditions for non-activated and activated cells. An increase of allergen and PHA stimulated IFN-gamma secretion in atopic children was found following cryopreservation, but no such increase in auto-antigen induced IFN-gamma was seen in MS-patients. The most consistent finding was that expression of IL-4 was generally decreased in spontaneous and auto-antigen/allergen induced expression in cryopreserved cells. In conclusion, this study points out the importance of investigation of the effects of freezing for each cytokine, stimuli and patient group before using frozen cells in studies of in vitro cytokine secretion.

Imbalance of T-cell subsets in angiotensin II-infused hypertensive rats with kidney injury

Blockade of angiotensin (Ang) II is efficient in various renal diseases. Although interest has focused on the hemodynamic changes and reduction of proteinuria, recent studies emphasize the nonhemodynamic effects of Ang II on kidney injury. The aim of this study was to clarify the mechanisms of Ang II on the immune system that alter the balance of helper T-cell (Th) subsets. We used a continuous, Ang II infusion model of rats that develop hypertension, proteinuria, and tubulointerstitial damage, including de novo expression of alpha-smooth muscle actin and loss of endothelial cells. We isolated T cells from the spleen and measured cytokine levels by ELISA systems. Ang II-infused rats showed an increase in the Th1 cytokine gamma-interferon and a decrease in the Th2 cytokine interleukin-4. The same change in cytokine mRNA expression in the spleen and kidney was confirmed by quantitative polymerase chain reaction analysis. Our ELISPOT assay showed an increase in the number of gamma-interferon-secreting T cells by Ang II. To investigate whether these changes were specific effects of Ang II, we treated the model rats with the Ang II receptor blocker (ARB) olmesartan or the nonspecific vessel dilator hydralazine. Administration of the ARB ameliorated disease manifestations and the imbalance in Th subsets, whereas hydralazine did not, despite comparable effects on blood pressure. These results demonstrate a direct role of Ang II in the modification of Th balance. The imbalance of Th subsets was associated with hypertensive kidney injury induced by Ang II. Some of the beneficial effects of ARBs might be explained by their immunomodulatory reactions.