Effect of eicosapentaenoic and docosahexaenoic acid on natural killer cell activity in human peripheral blood lymphocytes

The effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on natural killer (NK) cell activity in human peripheral blood lymphocytes were studied. The direct addition of trieicosapentaenoyl-glycerol (EPA-TG) or tridocosahexaenoylglycerol (DHA-TG) emulsion to a cytotoxicity assay system significantly suppressed NK cell activity. The addition of lipoxygenase inhibitor AA861 also inhibited NK cell activity. The inhibition was proportional to the concentration of EPA-TG emulsion. DHA-TG emulsion, or AA861. The presence of both EPA-TG emulsion or DHA-TG emulsion and AA861 at the same time led to a greater inhibitory effect on NK cell activity than when these emulsions were used separately. The inhibitory effect caused by these lipids or lipoxygenase blockade could not be reversed by adding back exogenous leukotrienes to the assay system. Preincubation of effector cells with EPA-TG or DHA-TG emulsion resulted in a significant inhibition of their NK cell activity. NK cell activity of human lymphocytes was markedly decreased after the infusion of EPA-TG emulsion into healthy volunteers. Thus, in vivo use of EPA-TG or DHA-TG emulsion may influence immune reactivity of the host, although the mechanism has not yet been elucidated.     

Dietary fish oil impairs induction of γ‐interferon and delayed‐type hypersensitivity during a systemic Salmonella enteritidis infection in rats

Snel J, Born L, van der Meer R. Dietary fish oil impairs induction of γ‐interferon and delayed‐type hypersensitivity during a systemic Salmonella enteritidis infection in rats. APMIS 2010; 118: 578–84. Fish oil that is rich in n‐3 polyunsaturated fatty acids markedly modulates immunological responses. Literature data indicate that the fish oil reduces cellular immunity and therefore impairs resistance to infections. We have investigated how dietary fish oil affects the immune response against a facultative intracellular pathogen, Salmonella enteritidis. Wistar rats were fed a diet containing 16% (w/w) of either fish oil or corn oil. After a 4‐week adaptation period, rats were intraperitoneally challenged with 4 × 10⁵ cfu of S. enteritidis. During the 14‐day infection period, urine was collected on a daily basis. At days 2 and 14, eight rats per group were sacrificed. Urinary nitrate, used as a marker for NO production, was lower on a fish oil diet during days 3–8. At day 2, serum γ‐interferon was 48 ± 7 pg/mL in the fish oil‐fed rats compared with 162 ± 52 pg/mL in the corn oil‐fed rats. No effects were found on living salmonella in liver and spleen. At day 14, as markers of an impaired T‐helper 1 (Th‐1) response, a 38% lower delayed‐type hypersensitivity responses and a lower salmonella‐specific IgG2b were observed in the fish oil‐fed rats. Although here dietary fish oil has affected only immune parameters, this impairment of the innate and Th‐1‐mediated immune response may have implications for the host resistance against other intracellular pathogens.     

Dietary n-3 polyunsaturated fatty acids modulate purified murine T-cell subset activation

Studies in humans and murine disease models have clearly shown dietary fish oil to possess anti-inflammatory properties, apparently mediated by the n-3 polyunsaturated fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). To determine the mechanisms by which dietary EPA and DHA modulate mouse T-cell activation, female C57BL/6 mice were fed diets containing either 2% safflower oil (SAF), 2% fish oil (FO), or a 2% purified EPA/DHA ethyl ester mixture for 14 days. Splenic CD4 T cells ( approximately 90% purity) or CD8 T cells ( approximately 85% purity) were incubated with agonists which act at the plasma membrane receptor level [anti(alpha)-CD3/anti(alpha)-CD28], the intracellular level (PMA/Ionomycin), or at both the receptor and intracellular levels (alphaCD3/PMA). CD4 T cells stimulated with alphaCD3/alphaCD28 or PMA/Ionomycin proliferated and produced principally IL-2 (i.e. a Th1 phenotype), whereas the proliferation of CD4 T cells stimulated with alphaCD3/PMA was apparently driven principally by IL-4 (i.e. a Th2 phenotype). The IL-4 driven proliferation of putative Th2 CD4 cells was enhanced by dietary n-3 fatty acids (P = 0.02). Conversely, IL-2 production by alphaCD3/alpha CD28-stimulated CD4 T cells was reduced in FO-fed animals (P < 0.0001). The alphaCD3/alphaCD28-stimulated CD8 cells cultured from FO-fed animals exhibited a significant decrease (P < 0.05) in proliferation. There were no dietary effects seen in alphaCD3/PMA-stimulated CD8 cells, which produced both IL-2 and IL-4, or in PMA/Ionomycin-stimulated CD8 cells, which produced principally IL-2. These data suggest that dietary n-3 fatty acids down-regulated IL-2 driven CD4 and CD8 activation, while up-regulating the activation of the Th2 CD4 T-cell subset. Thus, the anti-inflammatory effects of n-3 fatty acids may result in both the direct suppression of IL-2-induced Th1 cell activation and the indirect suppression of Th1 cells by the enhanced cross-regulatory function of Th2 cells.     

Differential effects of a saturated and a monounsaturated fatty acid on MHC class I antigen presentation

Lipid overload, associated with metabolic disorders, occurs when fatty acids accumulate in non-adipose tissues. Cells of these tissues use major histocompatibility complex (MHC) class I molecules to present antigen to T cells in order to eliminate pathogens. As obesity is associated with impaired immune responses, we tested the hypothesis that the early stages of lipid overload with saturated fatty acids (SFA) alters MHC class I antigen presentation. Antigen presenting cells (APC) were treated with either the saturated palmitic acid (PA), abundant in the high fat Western diet, or the monounsaturated oleic acid (OA), a component of the Mediterranean diet. PA-treatment lowered APC lysis by activated cytotoxic T lymphocytes and inhibited APC ability to stimulate naïve T cells. Inhibition of immune responses with PA was due to a significant reduction in MHC class I surface expression, inhibition in the rate of APC–T-cell conjugation, and lowering of plasma membrane F-actin levels. OA-treatment had no effect on antigen presentation and upon exposure with PA, prevented the phenotypic effects of PA. OA-treatment conferred protection against changes in antigen presentation by accumulating fatty acids into triglyceride-rich lipid droplets of APC. Our findings establish for the first time a link between the early stages of lipid overload and antigen presentation and suggest that dietary SFA could impair immunity by affecting MHC I-mediated antigen presentation; this could be prevented, paradoxically, by accumulation of triglycerides rich in monounsaturated fatty acids.     

Th1 cytokines promote T-cell binding to antigen-presenting cells via enhanced hyaluronan production and accumulation at the immune synapse

Hyaluronan (HA) production by dendritic cells (DCs) is known to promote antigen presentation and to augment T-cell activation and proliferation. We hypothesized that pericellular HA can function as intercellular ‘glue'' directly mediating T cell–DC binding. Using primary human cells, we observed HA-dependent binding between T cells and DCs, which was abrogated upon pre-treatment of the DCs with 4-methylumbelliferone (4-MU), an agent which blocks HA synthesis. Furthermore, T cells regulate HA production by DCs via T cell-derived cytokines in a T helper (Th) subset-specific manner, as demonstrated by the observation that cell-culture supernatants from Th1 but not Th2 clones promote HA production. Similar effects were seen upon the addition of exogenous Th1 cytokines, IL-2, interferon γ (IFN-γ) and tumor necrosis factor α (TNF-α). The critical factors which determined the extent of DC–T cell binding in this system were the nature of the pre-treatment the DCs received and their capacity to synthesize HA, as T-cell clones which were pre-treated with monensin, added to block cytokine secretion, bound equivalently irrespective of their Th subset. These data support the existence of a feedforward loop wherein T-cell cytokines influence DC production of HA, which in turn affects the extent of DC–T cell binding. We also document the presence of focal deposits of HA at the immune synapse between T-cells and APC and on dendritic processes thought to be important in antigen presentation. These data point to a pivotal role for HA in DC–T cell interactions at the IS.     

Dietary nucleotides can up-regulate antigen-specific Th1 immune responses and suppress antigen-specific IgE responses in mice

BACKGROUND: It has been reported that dietary nucleotides enhance T helper cell activities. In this study, we have determined the effects of dietary nucleotides on antigen-specific Th1 and Th2 responses and IgE responses. METHODS: Ovalbumin (OVA)-specific T cell receptor (TCR) transgenic (OVA-TCR Tg) mice, 3 weeks old, were fed a nucleotide-free diet (NT(-) diet) or the NT(-) diet supplemented with dietary nucleotides (NT(+) diet) for 4 weeks. Cytokine production by spleen cells and macrophages obtained from these mice was measured in vitro. BALB/c mice, 3 weeks old, immunized intraperitoneally with OVA adsorbed onto alum, were fed the NT(-) diet or the NT(+) diet for 4 weeks. Serum levels of antigen-specific antibodies in the BALB/c mice were determined by ELISA. RESULTS: The level of production of antigen-specific interferon-gamma by spleen cells was significantly higher in the OVA-TCR Tg mice fed the NT(+) diet than in the control mice. The levels of secretion of bioactive IL-12 by spleen cells and peritoneal macrophages were also significantly increased in the NT(+) diet group. The serum OVA-specific IgE level was significantly decreased in BALB/c mice fed the NT(+) diet compared with those fed the NT(-) diet. CONCLUSION: These results show that dietary nucleotides up-regulate the antigen-specific Th1 immune response through the enhancement of IL-12 production and suppress the antigen-specific IgE response.     

Dietary fatty acids influence the production of Th1- but not Th2-type cytokines

C57B16 mice were fed for 6 weeks on a low-fat diet or on high-fat diets containing coconut oil (rich in saturated fatty acids), safflower oil [rich in n-6 polyunsaturated fatty acids (PUFAs)], or fish oil (rich in n-3 PUFAs) as the main fat sources. The fatty acid composition of the spleen lymphocytes was influenced by that of the diet fed. Thymidine incorporation into concanavalin A-stimulated spleen lymphocytes and interleukin (IL)-2 production were highest after feeding the coconut oil diet. Interferon (IFN)-gamma production was decreased by safflower oil or fish oil feeding. IL-4 production was not significantly affected by diet, although production was lowest by lymphocytes from fish oil-fed mice. The ratio of production of Th1- to Th2-type cytokines (determined as the IFN-gamma/IL-4 ratio) was lower for lymphocytes from mice fed the safflower oil or fish oil diets. After 4 h of culture, IL-2 mRNA levels were higher in cells from mice fed coconut oil, and IFN-gamma mRNA levels were higher in cells from mice fed coconut oil or safflower oil. After 8 h of culture, IL-2, IFN-gamma, and IL-4 mRNA levels were lowest in cells from mice fed fish oil. The ratio of the relative levels of IFN-gamma mRNA to IL-4 mRNA was highest in cells from mice fed coconut oil and was lowest in cells of mice fed fish oil. The influence of individual fatty acids on IL-2 production by murine spleen lymphocytes was examined in vitro. Although all fatty acids decreased IL-2 production in a concentration-dependent manner, saturated fatty acids were the least potent and n-3 PUFAs the most potent inhibitors, with n-6 PUFAs falling in between in terms of potency. It is concluded that saturated fatty acids have minimal effects on cytokine production. In contrast, PUFAs act to inhibit production of Th1-type cytokines with little effect on Th2-type cytokines; n-3 PUFAs are particularly potent. The effects of fatty acids on cytokine production appear to be exerted at the level of gene expression.     

The role of small intestinal antigen-presenting cells in the induction of T-cell reactivity to soluble protein antigens: association between aberrant presentation in the lamina propria and oral tolerance.

The oral administration of soluble protein antigen results in profound immunological tolerance. However, the tissue location and function of antigen-presenting cells (APC) that stimulate this response remain unclear. We have hypothesized that the properties of cells presenting antigen to naive T cells within the gut are involved, and therefore gut APC should stimulate T-cell responses with different characteristics to those induced by other APC. To test this, we studied in vitro primary T-cell responses following presentation of soluble protein antigen by cells from the Peyer's patches (PPC) and lamina propria (LPC) of the murine small intestine and the spleen (SPLC). Each APC population stimulated antigen-specific proliferative responses with similar anamnestic characteristics; however, analysis of the cytokines produced revealed marked differences. Whereas SPLC stimulated the balanced production of T-helper type 1 (Th1) and Th2 cytokines, PPC induced a profile consistent with the provision of T-cell help for IgA production. Interestingly, presentation of antigen by LPC stimulated high levels of interferon-gamma (IFN-gamma) and transforming growth factor-beta (TGF-beta) in the absence of other cytokines [interleukin-2 (IL-2), IL-4, IL-5]. Evidence from analysis of cell activation and division within the cultures suggested that this profile may result from the preferential activation of CD8+ T cells by LPC; however, the lack of conventional CD4+ T-cell cytokines indicated a defect in the normal function of these cells. Adoptive transfer of antigen-pulsed LPC to syngeneic animals abrogated the induction of delayed-type hypersensitivity (DTH) responsiveness, which followed a subsequent conventional antigen challenge further suggesting a role for lamina propria APC in tolerance induction.     

Presentation of the candidate rheumatoid arthritis autoantigen aggrecan by antigen-specific B cells induces enhanced CD4(+) T helper type 1 subset differentiation

Effective immune responses require antigen uptake by antigen-presenting cells (APC), followed by controlled endocytic proteolysis resulting in the generation of antigen-derived peptide fragments that associate with intracellular MHC class II molecules. The resultant peptide-MHC class II complexes then move to the APC surface where they activate CD4(+) T cells. Dendritic cells (DC), macrophages and B cells act as efficient APC. In many settings, including the T helper type 1 (Th1) -dependent, proteoglycan-induced arthritis model of rheumatoid arthritis, accumulating evidence demonstrates that antigen presentation by B cells is required for optimal CD4(+) T cell activation. The reasons behind this however, remain unclear. In this study we have compared the activation of CD4(+) T cells specific for the proteoglycan aggrecan following antigen presentation by DC, macrophages and B cells. We show that aggrecan-specific B cells are equally efficient APC as DC and macrophages and use similar intracellular antigen-processing pathways. Importantly, we also show that antigen presentation by aggrecan-specific B cells to TCR transgenic CD4(+) T cells results in enhanced CD4(+) T cell interferon-γ production and Th1 effector sub-set differentiation compared with that seen with DC. We conclude that preferential CD4(+) Th1 differentiation may define the requirement for B cell APC function in both proteoglycan-induced arthritis and rheumatoid arthritis.     

Establishment of stable CD8+ suppressor T cell clones and the analysis of their suppressive function.

Stable CD8+ suppressor T cell (Ts) clones were established by a relatively simple method. Keyhole limpet hemocyanin (KLH)-primed spleen cells from C3H mice were depleted of B cells and CD4+ T cells by panning and cytotoxic treatment, and the resulting CD8+ T cells were periodically stimulated with antigen and irradiated syngeneic spleen cells followed by manifestation in interleukin-2 (IL-2) containing medium. T cell clones with a definite suppressor function were established by limiting dilution. They were defined as classical effector type Ts of CD8+ phenotype as they had constant and definite suppressor functions in antigen-induced T cell proliferation and specific antibody response against T cell-dependent antigens without detectable cytotoxic activity against both antigen presenting cells (APC) and helper T cells (Th). They showed no helper activity for B cells and produced no detectable helper type lymphokines such as IL-2 and IL-4. CD8+ Ts clones were able to inhibit the antigen-induced IL-2 production of normal and cloned T cells. Their suppressive activity was antigen-nonspecific and major histocompatibility complex-unrestricted. CD8+ Ts clones were also able to suppress the proliferative response of Th clones induced by immobilized anti-T cell receptor (TcR) and anti-CD3 mAbs but not the response induced by concanavalin A (ConA) and IL-2. All the CD8+ T cell clones established independently utilized the TcR V beta 8 gene. Syngeneic antigen presenting cells could induce proliferation of these CD8+ clones, which was blocked by anti-CD8 and anti-I-Ak monoclonal antibody (mAb) but not by anti-class I mAbs. The stimulation of CD8+ Ts clones with immobilized anti-CD3 resulted in the release of a suppressor factor(s) that potently inhibited the antigen-induced proliferation of CD4+ Th clones and the in vitro secondary antibody formation.     

Negative feedback mechanism suppresses interleukin-12 production by antigen-presenting cells interacting with T helper 2 cells

Interleukin-12 (IL-12) has been shown to be produced by monocytes by the ligation of CD40. In the present experiments, IL-12 is shown to be produced by murine spleen antigen-presenting cells (APC) by interaction with T helper 1 (Th1) 1 clones through CD40-CD40 ligand (CD40L) interaction, but not with Th2 clones. The IL-12 production induced by the Th1 clone interaction was inhibited by the addition of exogenous IL-10. Th2 clones were shown to produce a sufficient amount of IL-10 to inhibit the IL-12 production induced by Th1 clones. In the presence of anti-IL-10 monoclonal antibodies splenic APC interacting with Th2 clones produced IL-12. These results indicate that IL-10 produced by Th2 cells stimulated with antigen suppress IL-12 production of APC interacting with Th2 cells. IL-12 is composed of two subunits, p35 and p40. In our experiments, p40 mRNA accumulation was shown to be affected by IL-10 more severely than the accumulation of p35 mRNA, indicating that IL-10 regulates IL-12 production by APC mainly by affecting p40 mRNA accumulation.     

Long-chain polyunsaturated fatty acids are consumed during allergic inflammation and affect T helper type 1 (Th1)- and Th2-mediated hypersensitivity differently

Studies have shown that atopic individuals have decreased serum levels of n‐3 fatty acids. Indicating these compounds may have a protective effect against allergic reaction and/or are consumed during inflammation. This study investigated whether fish (n‐3) or sunflower (n‐6) oil supplementation affected T helper type 1 (Th1)‐ and Th2‐mediated hypersensitivity in the skin and airways, respectively, and whether the fatty acid serum profile changed during the inflammatory response. Mice were fed regular chow, chow + 10% fish oil or chow + 10% sunflower oil. Mice were immunized with ovalbumin (OVA) resolved in Th1 or Th2 adjuvant. For Th1 hypersensitivity, mice were challenged with OVA in the footpad. Footpad swelling, OVA‐induced lymphocyte proliferation and cytokine production in the draining lymph node were evaluated. In the airway hypersensitivity model (Th2), mice were challenged intranasally with OVA and the resulting serum immunoglobulin (Ig)E and eosinophilic lung infiltration were measured. In the Th1 model, OVA‐specific T cells proliferated less and produced less interferon (IFN)‐γ, tumour necrosis factor (TNF) and interleukin (IL)‐6 in fish oil‐fed mice versus controls. Footpad swelling was reduced marginally. In contrast, mice fed fish oil in the Th2 model produced more OVA‐specific IgE and had slightly higher proportions of eosinophils in lung infiltrate. A significant fall in serum levels of long‐chain n‐3 fatty acids accompanied challenge and Th2‐mediated inflammation in Th2 model. Fish oil supplementation affects Th1 and Th2 immune responses conversely; significant consumption of n‐3 fatty acids occurs during Th2‐driven inflammation. The latter observation may explain the association between Th2‐mediated inflammation and low serum levels of n‐3 fatty acids.     

Antigenic dietary protein guides maturation of the host immune system promoting resistance to Leishmania major infection in C57BL/6 mice

The immature immune system requires constant stimulation by foreign antigens during the early stages of life to develop properly and to create efficient immune responses against later infections. We have previously shown that intake of antigenic dietary protein is critical for inducing maturation of the immune system as well as for the development of T helper type 1 (Th1) immunity. In this study, we show that administration of an amino acid (aa)‐based diet during the development of the immune system subsequently resulted in inefficient control of Leishmania major infection in adult C57BL/6 mice. Compared with mice fed a control protein‐containing diet, adult aa‐fed mice showed a decreased interferon (IFN)‐γ response to parasite antigens and insufficient production of nitric oxide (NO), which is crucial to parasite death. However, no deviation towards Th2‐specific immunity to L. major was observed. Phenotypic analysis of antigen‐presenting cells (APCs) from aa‐fed mice revealed deficient levels of the costimulatory molecules CD40 and CD80, and low levels of interleukin (IL)‐12 produced by peritoneal macrophages, revealing an early stage of maturation of these cells. APCs isolated from aa‐fed mice were unable to stimulate a Th1 response in vitro. Both phenotypic features of T cells from aa‐fed mice and their ability to produce a Th1 response in the presence of mature APCs were unaffected when compared with T cells from control mice. The results presented here support the notion that regulation of Th1 immunity to infection includes environmental factors such as dietary proteins, which provide a natural source of stimulation that contributes to the process of maturation of APCs.     

The influence of dietary protein antigen on Th1/Th2 balance and cellular immunity.

Dietary administration of ovalbumin (OVA) antigen (Ag) into OVA-specific T cell receptor alphabeta-transgenic (TCR-Tg) mice resulted in the induction of activated CD4+ Th cells expressing CD69 early activation Ag. However, the number of CD4+ Th cells rather decreased by dietary administration of OVA antigen. The production of Th1-cytokines such as IFN-gamma and IL-2 markedly reduced in spleen of OVA-fed mice compared to mice fed with normal diet. In sharp contrast, the production of Th2-cytokine, IL-4 greatly increased in spleen of OVA-fed mice though the number of CD4+ T cells decreased to less than 10% of control mouse spleen. The decrease of IFN-gamma production and the increase of IL-4 production by CD4+ T cells was demonstrated at a single cell level by intracellular cytokine staining analysis. Moreover, such a polarized cytokine production pattern was also demonstrated using highly purified CD4+ T cells obtained from mice fed with OVA. In addition to the decrease of Th1-cytokine production, TCR-Tg mice fed with OVA-containing diet showed greatly reduced in vivo generation of NK cells, LAK cells and CTL. These results suggested that dietary protein antigen caused the polarization of Th1/Th2 balance into Th2-dominant immunity and inhibited cellular immunity.     

Characterization of rat T helper cell clones specific for Bacteroides gingivalis antigen.

During the past several years, much interest has been directed towards delineating and characterizing different subsets of T helper (Th) cells in order to understand their roles in immune processes. In this study, we report the generation of antigen-specific rat Th cell clones and their characterization in terms of phenotype, function, and lymphokine production. The clones were derived by culturing purified splenic T cells from rats immunized with the pathogen Bacteroides gingivalis with equivalent numbers of irradiated spleen cells from nonimmune rats and B. gingivalis whole-cell antigen. The clones required antigen stimulation but not exogenously added interleukin-2 for growth and were maintained in culture for approximately 6 months. The cloned T cells proliferated in response to the mitogen concanavalin A and to B. gingivalis whole-cell antigen but not to other microbial antigens. Phenotypic characterization of the cloned T cells for cell surface markers demonstrated that these cells were OX19+ W3/25+ OX8- OX22- and therefore probably represented a mature subpopulation of CD4+ Th cells. These cloned T cells were positive for interleukin-2 receptor expression. Culture supernatants from the Th cell clones which were collected at various times after antigen stimulation exhibited low interleukin-2 activity and high gamma interferon activity. This in vitro study provides evidence of a rat Th cell subset that could represent an important population in regulating immune responses to microbial antigens.     

MaxEPA fish oil enhances cholesterol-induced intimal foam cell formation in rabbits.

In this study, the cholesterol-fed rabbit model was used to test the hypothesis that fish oil supplementation can influence the initiation and development of atherosclerotic lesions. Rabbits were fed one of two diets for a period of 30 days: a nonatherogenic diet with corn oil as the sole fat source, or an atherogenic diet containing beef tallow and cholesterol. In addition, animals received a daily supplement of either MaxEPA fish oil or corn oil (0.5 ml/kg body weight). Terminal blood samples were drawn and the cholesterol and triglyceride levels determined for both plasma and very low-density (VLDL), intermediate-density (IDL), low-density (LDL), and high-density (HDL) lipoproteins. Thiobarbituric acid-reacting substance (TBARS), an indicator of lipid peroxidation, was measured in the plasma samples. Besides these biochemical parameters of atherogenesis, the number of intimal foam cells in the descending thoracic aorta of each animal was determined by microscopic examination of the vessels en face. In rabbits fed the nonatherogenic diet, fish oil supplementation did not significantly affect any of the biochemical parameters that were measured. In contrast, fish oil supplementation of the atherogenic diet led to a significant increase in the LDL- and HDL-cholesterol as well as the HDL-triglyceride levels. Plasma TBARS also increased more than four times. Morphologic analysis of the vessels from rabbits fed the atherogenic diet indicated that fish oil supplementation led to a threefold increase in the number of intimal foam cells, a result that may be linked to increases in both LDL-cholesterol and plasma TBARS. The results of these experiments do not support the hypothesis that dietary fish oil will inhibit the initiation or progression of lesion formation in the cholesterol-fed rabbit.     

Defective Th1 and Th2 cytokine synthesis in the T-T cell presentation model for lack of CD40/CD40 ligand interaction

In this study, T or NK cell clones used as antigen-presenting cells (T- or NK-APC) were shown to be significantly less efficient than professional APC in inducing Th1 and Th2 cytokines by antigen-specific T cell clones. This phenomenon was not related to a limited engagement of TCR by T-APC, since comparable thresholds of TCR down-regulation were shown when antigen was presented by either T-APC or professional APC. Rather, the stimulatory T-APC weakness was due to their inability, because they are CD40⁻, to provide the appropriate co-stimuli to responder T cells both indirectly via IL-12, and partially via direct CD40L triggering on T cells. Indeed, the simultaneous addition of IL-12 and reagents directly engaging CD40L on responder T cells restored T cell cytokine synthesis when antigen was presented by T-APC. In addition, either IL-12 production or blocking of T cell cytokine synthesis by anti-IL-12 p75 antibodies was evident only when professional APC were used in our antigen-specific system. The down-regulation of cytokine synthesis in the system of T-T cell presentation could represent a novel mechanism of immune regulation, which may intervene to switch off detrimental Th1- or Th2-mediated responses induced by antigen presentation among activated T cells infiltrating inflamed tissues.     

The type of dietary fat affects the severity of autoimmune disease in NZB/NZW mice.

The type of dietary fat dramatically affects the onset of autoimmune disease in lupus-prone female New Zealand Black/New Zealand White F1 (B/W) mice. Disease development was strikingly slowed in mice fed a diet containing quantities of omega-3 fatty acids (fish oil, FO). By 10 months of age, 94% of the FO mice were still living, whereas all the mice fed a saturated fat diet (lard,L) were dead. Those mice fed a corn oil (CO) diet were intermediate with 35% alive at the 10-month time evaluation. Long after the L and CO groups had succumbed to glomerulonephritis, the FO group had negligible proteinuria. Both B and T cell function, particularly antibody production and resultant circulating immune complex (CIC) levels, were modified by the type of dietary fat. FO mice exhibited lower levels of anti-ds-DNA and lower levels of CICs than L or CO mice. B/W antibody response to a T-independent antigen (DNP-dextran) was enhanced at 8 months of age in FO mice, whereas it was suppressed in L mice. T-dependent (sheep red blood cell) responses at that time period were reduced in all the diet groups, a reflection of the reduced numbers of accessory T cells as determined by FACS analysis. The natural killer (NK) response to YAC-1 cells decreased in the L group from 5 to 9 months of age but remained unchanged in the CO and FO groups. Severe glomerulonephritis was the most common histopathologic finding in the L and CO groups. Arteritis was found in the spleens of nearly all the L and CO mice. Arteritis of the heart, colon and intestine, stomach, kidney, and liver were also seen principally in the L mice. In contrast, most FO mice had minimal to mild glomerulonephritis and no or minimal arteritis in the spleen. It is likely omega-3 fatty acids of fish oil reduce immune-complex-induced glomerulonephritis through production of prostaglandin metabolites with attenuated activity and/or through altering cell membrane structure and fluidity, which may, in turn, affect the responsiveness of immune cells.     

Cholera Toxin Enhances Alloantigen Presentation by Cultured Intestinal Epithelial Cells

In the present study we show that cholera toxin (CT) strongly potentiates antigen presentation by intestinal epithelial cells, probably by enhancing co-stimulation. This was demonstrated in an allogeneic system using cells from the IEC-17 rat epithelial cell line as antigen presenting cells (APC). These cells were induced by optimal concentrations of IFN-γ to express good amounts of Ia antigen and cultured for 24–48 h in the presence or absence of CT. Thereafter the cells were thoroughly washed and added to cultures containing MHC-incompatible spleen cells as responder cells. Epithelial cells exposed to CT demonstrated greatly enhanced ability to trigger allogen-specific T-cell proliferation as compared with IEC-17 cells treated with IFN-γ alone. The mechanism for the enhanced APC function was investigated by analysing CT-treated IEC-17 cells for increased class II MHC antigen expression or enhanced production of cytokines with known co-stimulatory function. We found no significant increase in class II MHC antigen expression. By contrast, CT strongly promoted, in a dose-dependent fashion, the production of both IL-1 and IL-6 cytokines by IEC-17 cells as compared with untreated epithelial cells. This effect of CT was specific and not due to contaminating endotoxin because excess amounts of soluble toxin receptor, ganglioside GM1, added to the IEC-17 cultures completely abrogated the cytokine response to CT. These results together with our previous findings of enhanced antigen presentation by macrophages stimulated by CT suggest that the potent adjuvant function of CT for induction of mucosal immune responses might be attributed to an enhanced co-stimulating ability of several putative APC in the mucosal immune system: macrophages, B cells and epithelial cells.     

HLA Class II+ Human Keratinocytes present Mycobacterium leprae Antigens to CD4+ Thl-Like Cells

In a variety of inflammatory skin diseases like leprosy, keratinocytes (KC) are induced to express MHC class II molecules and may therefore serve as antigen-presenting cells (APC) for MHC class II restricted T cells infiltrating the lesions. However, KC have been thought to be improper APC for MHC class II restricted T cells and to drive T cells into an anergic rather than into an activation state. We evaluated this issue in relation to leprosy and tested whether HLA-DR⁺ KC could present M. leprae antigens to well-defined, CD4 ⁺, cytotoxic as well as proliferative, Thl -like cell clones. Using a recently developed sensitive assay system which employs intact layers of basal KC as APC we found that most T-cell clones (6/8) lysed HLA-DR⁺ KC pulsed with M. leprae antigens. KC were only recognized after induction of HLA-DR expression by IFN-γ, in an antigen-specific and HLA class II restricted manner. All T-cell clones tested also showed significant proliferation and IFN-γ production in response to M. leprae antigens presented by HLA-DR⁺ KC, arguing against a KC dependent anergizing effect on T cells. Thus, HLA class II⁺ KC can function as proper APC for HLA class II restricted CD4⁺ Th l -like cells. It seems therefore possible that antigen presentation by KC contributes to the local cell-mediated immune responses in DTH lesions.