Phagocytosis of antigens by Langerhans cells

Dendritic Cells Enhance HIV Infection of Memory CD4(+) T Cells in Human Lymphoid Tissues

Dendritic cells (DCs) play a key role in controlling infections by coordinating innate and adaptive immune responses to invading pathogens. Paradoxically, DCs can increase HIV-1 dissemination in vitro by binding and transferring infectious virions to CD4(+) T cells, a process called transinfection. Transinfection has been well characterized in cultured cell lines and circulating primary T cells, but it is unknown whether DCs enhance infection of CD4(+) T cells in vivo. In untreated HIV infection, massive CD4(+) T-cell infection and depletion occur in secondary lymphoid tissues long before decline is evident in the peripheral circulation. To study the role of DCs in HIV infection of lymphoid tissues, we utilized human tonsil tissues, cultured either as tissue blocks or as aggregate suspension cultures, in single-round infection experiments. In these experiments, addition of monocyte-derived DCs (MDDCs) to the cultures increased T-cell infection, particularly in CD4(+) T cells expressing lower levels of HLA-DR. Subset analysis demonstrated that MDDCs increased HIV-1 infection of central and effector memory T-cell populations. Depletion of endogenous myeloid DCs (myDCs) from the cultures decreased memory T-cell infection, and readdition of MDDCs restored infection to predepletion levels. Using an HIV-1 fusion assay, we found that MDDCs equally increased HIV delivery into naïve, central, and effector memory T cells in the cultures, whereas predepletion of myDCs reduced fusion into memory T cells. Together, these data suggest that resident myDCs facilitate memory T-cell infection in lymphoid tissues, implicating DC-mediated transinfection in driving HIV dissemination within these tissues in untreated HIV/AIDS.

Recruitment of dendritic cells in human liver with metastases

Dendritic cells (DCs) play a key role in the generation of antitumor immune responses as the most potent professional antigen-presenting cells. In this study we examined the distribution of DCs subsets in selected areas of liver metastases and adjacent liver tissue of 74 patients with gastrointestinal cancers (14 gastric, 47 colon, and 13 rectal) using immunohistochemistry for the DCs markers S-100 protein, HLA-DR, CD1a, and CD83. S-100 protein-positive DCs were localized mainly in clusters in metastases and at the tumor border with the surrounding liver tissue, while HLA-DR-positive DCs were significantly more in number (P<0.0001) and were diffusely distributed in metastasis stroma and at the tumor border. S-100 protein-positive DCs with mature phenotype were presented around metastases and in the sinusoidal lumena, whereas S-100 protein-positive DCs with less mature phenotype based on their ultrastructure were scattered in the tumor stroma. CD1a- and CD83-positive DCs were observed predominantly in small groups or as single cells in the tumor stroma and in the invasive margin. The numbers of CD1a-positive DCs (immature) and CD83-positive DCs (mature) were comparable, but significantly lower than that of S-100 protein-positive (P<0.0001) and HLA-DR-positive cells (P<0.0001).We observed more S-100 protein-positive DCs and HLA-DR-expressing cells in the sinusoids and portal tracts of the liver tissue, surrounding metastases, than in control liver tissue. In conclusion, this study provides additional information on the functional subtypes and distribution of DCs infiltrating metastatic tissue and local liver environment in patients with liver metastases from gastrointestinal cancers.

Monocyte-derived dendritic cells activated by bacteria or by bacteria-stimulated epithelial cells are functionally different

Dendritic cells (DCs) are able to open the tight junctions between adjacent epithelial cells (ECs) and to take up both invasive and noninvasive bacteria directly from the intestinal lumen. In this study, we describe a tight cross talk between ECs and human monocyte-derived DCs (MoDCs) in bacterial handling across epithelial monolayers. We show that the release of proinflammatory mediators by ECs in response to bacteria is dependent on bacterial invasiveness and on the presence of flagella. This correlates with the capacity of EC-derived factors to modulate MoDC function. MoDCs incubated with supernatants of bacteria-treated ECs are "noninflammatory" as they release interleukin-10 (IL-10) but not IL-12 and can drive only T helper (Th)-2 type T cells. Moreover, noninflammatory MoDCs release chemokines aimed at recruiting Th2 and T-regulatory cells. In contrast, when MoDCs are incubated with ECs and bacteria in a transwell coculture system, and can contact directly the bacteria across stimulated EC monolayers, they are more inflammatory as they release IL-12 and IL-10 and induce both Th1 and Th2 responses. These results suggest that ECs are not simply a barrier to bacteria entering via the oral route, but they actively influence the activating properties of DCs.

Uptake and presentation of orally administered antigens

The mucosae of the gastrointestinal tract are continuously exposed to a myriad of antigens and microorganisms that the immune system has to discriminate between dangerous and harmless. Entry of pathogenic microorganisms occurs mainly via M cells that are concentrated in the follicle-associated epithelium overlying the Peyer's Patches (PPs). M cells are very selective and do not allow entry of all microorganisms. We have recently described an additional mechanism by which dendritic cells (DCs) can monitor the contents of the intestinal lumen. DCs send dendrites outside the epithelium, like periscopes. It is not clear whether this mechanism is constitutively active or is induced in response to signals from epithelial cells that have been in contact with pathogens or high numbers of non pathogenic bacteria in the lumen. Therefore, deciphering the signals that are released by epithelial cells after the encounter with mucosal antigens is of paramount importance to understand the ability of the DCs to respond to the different antigens and to mount immune or tolerogenic responses.

Intestinal Epithelial Cells Control Dendritic Cell Function

Dendritic cells (DCs) comprise a family of cells specializing in antigen capture and presentation to T cells. We have recently shown that DC play an active role in bacterial uptake across mucosal surfaces. Indeed, DC are able to open tight junctions and to sample antigens directly across epithelia, both in vitro and in vivo. Because DC express tight junction proteins, the integrity of the epithelial barrier is preserved. In this study we have analyzed the possible involvement of epithelial cells in controlling DC function. We developed an in vitro model in our laboratory consisting of a three-player system of dendritic cells, epithelial cell monolayers, and bacteria. The crosstalk between epithelial cells and dendritic cells was analyzed, and epithelial cells were tested for their capacity to release cytokines and chemokines that induce the migration and activation of DC. We show that the capacity of epithelial cells to produce cytokines and activate DC is dependent on the invasiveness of the bacteria tested. In particular, invasive bacteria stimulate epithelial cells to release proinflammatory cytokines and to induce the maturation state of DC. By contrast, noninvasive bacteria are unable to stimulate epithelial cells, but can activate DC directly when DC translocate to the apical side. In conclusion, epithelial cells are not simply a barrier to bacteria entering via the oral route, but actively influence the activating properties of bystander DC.

Phagocytosis and phagosomal fate of surface-modified microparticles in dendritic cells and macrophages

PURPOSE

We compared cationic, polyamine-coated microparticles (MPs) and anionic, protein-coated MPs with respect to their phagocytosis and phagosomal fate in dendritic cells (DCs) and macrophages (Mphi).

METHODS

Polystyrene MPs were surface modified by covalent coupling with fluorescein isothiocyanate-labeled polyamines or proteins. Phagocytosis of MP and the pH of their intracellular microenvironment was assessed in human-derived DCs and Mphi in a fluorescence plate reader. Visualization of MP phagocytosis in DCs was performed by transmission electron microscopy.

RESULTS

Phagocytosis of bovine serum albumin-coated MPs was low with significant differences between DC and Mphi, whereas phagocytosis of IgG-coated MPs was significantly enhanced in both cell types. Phagocytosis of both particle types resulted in an acidified phagosomal microenvironment (pH 4.6-5.1). In contrast, cationic, polyamine-coated MPs were equally phagocytosed by DCs and Mphi to a high extent and showed lower degrees of acidification (pH 6.0-6.8) in the phagosomal microenvironment. Transmission electron microscopy examination demonstrated all phagocytosed particles to be surrounded by a phagosomal membrane, which was more tightly apposed to the surface of cationic MPs and more loosely to bovine serum albumin-coated MPs.

CONCLUSION

Phagocytosis of cationic, polyamine-coated MPs is suggested to lead to diminished phagosomal acidification. Thus, cationic MP are potential carriers that may display beneficial features for the intracellular delivery of immunomodulating therapeutics and their protection against lysosomal degradation.

Gene gun-mediated DNA immunization primes development of mucosal immunity against bovine herpesvirus 1 in cattle

Vaccination by a mucosal route is an excellent approach to the control of mucosally acquired infections. Several reports on rodents suggest that DNA vaccines can be used to achieve mucosal immunity when applied to mucosal tissues. However, with the exception of one study with pigs and another with horses, there is no information on mucosal DNA immunization of the natural host. In this study, the potential of inducing mucosal immunity in cattle by immunization with a DNA vaccine was demonstrated. Cattle were immunized with a plasmid encoding bovine herpesvirus 1 (BHV-1) glycoprotein B, which was delivered with a gene gun either intradermally or intravulvomucosally. Intravulvomucosal DNA immunization induced strong cellular immune responses and primed humoral immune responses. This was evident after BHV-1 challenge when high levels of both immunoglobulin G (IgG) and IgA were detected. Intradermal delivery resulted in lower levels of immunity than mucosal immunization. To determine whether the differences between the immune responses induced by intravulvomucosal and intradermal immunizations might be due to the efficacy of antigen presentation, the distributions of antigen and Langerhans cells in the skin and mucosa were compared. After intravulvomucosal delivery, antigen was expressed early and throughout the mucosa, but after intradermal administration, antigen expression occurred later and superficially in the skin. Furthermore, Langerhans cells were widely distributed in the mucosal epithelium but found primarily in the basal layers of the epidermis of the skin. Collectively, these observations may account for the stronger immune response induced by mucosal administration.