Role of macrophages as modulators but not as autonomous accessory cells in the proliferative response of immune T cells to soluble antigen

Effects of nanoparticle surface-coupled peptides, functional endgroups, and charge on intracellular distribution and functionality of human primary reticuloendothelial cells

The medical use of nanoparticles (NPs) has to consider their interactions with the cells of the reticuloendothelial system. In this study the authors used gold nanorods coated by PEG chains bearing peptides or charged functional groups to study their influence on the uptake, subcellular distribution, and activation of human primary reticuloendothelial cells: monocytes, macrophages (MΦ), immature and mature dendritic cells (DC), and endothelial cells (EC). We found that beside MΦ and immature DC also EC internalize large quantities of NPs and observed an increased uptake of positively charged particles. Most notably, NPs accumulated in the MHC II compartment in mature DC that is involved in antigen processing. Furthermore, surface-coupled peptide sequences RGD and GLF altered the activation profile of DC, and modulated cytokine release in both DC and MΦ in a cell specific manner. These data suggest that the charge of NPs mainly influences their uptake, whereas conjugated peptides alter cell functions.

FROM THE CLINICAL EDITOR

In this paper the interactions between RES cells and nanoparticles is investigated, concluding that in the case of gold nanorods charge determines uptake characteristics, whereas conjugated peptides determine their function.

Antigen-presenting capacity of macrophages and dendritic cells in the peritoneal cavity of patients treated with peritoneal dialysis

In this study the antigen-presenting capacity of human peritoneal cells and the influence of continuous ambulant peritoneal dialysis (CAPD) were studied. On average 6% of the peritoneal cells were dendritic cells (DC), with no difference between CAPD and control peritoneal cells. DC were enriched by selecting for non-adherent, Fc receptor-negative, low density cells. A typical spot-like CD68 positivity was seen in DC, in contrast to the pancytoplasmic staining pattern in macrophages. Peritoneal DC morphologically and functionally showed features of cells belonging to the DC lineage. Peritoneal DC were superior antigen-presenting cells for both allo-antigen, and Candida albicans antigen or purified protein derivative. CAPD peritoneal macrophages were two- to three-fold better stimulator cells for allogeneic T cells compared with control macrophages. The level of integrins/adhesins or MHC class I or II, as measured semi-quantitatively on the FACS, could not account for this phenomenon. In addition, a double chamber system showed that dialysate-activated macrophages produced soluble factors that could enhance DC-induced allogeneic T cell proliferation. In conclusion, human peritoneal cells contain a relatively high percentage of classical DC. CAPD treatment does not impair the antigen-presenting capacity of peritoneal cells, but instead upregulates the allo-antigen-presenting capacity of peritoneal macrophages.

Localization of interleukin-1 (IL-1) mRNA-expressing macrophages in human inflamed gingiva and IL-1 activity in gingival crevicular fluid

The exact cell type and site(s) involved in interleukin-1 (IL-1) production during gingival inflammation was determined by combining immunohistochemistry and in situ hybridization. IL-1 messenger RNA (mRNA)-expressing cells in human inflamed gingiva were identified as macrophages. The rate of IL-alpha mRNA expression in these macrophages was the same as IL-1 beta mRNA expression. The rate of IL-1 mRNA expression was higher in connective tissue furthest from the pocket epithelium, although more macrophages were present at the connective tissue subjacent to the pocket epithelium. The IL-1 activity in gingival crevicular fluid (GCF) obtained from inflamed gingiva was higher than that from healthy gingiva and decreased after periodontal therapy. The IL-1 activity in GCF was almost completely abolished by the addition of anti-IL-1 alpha antibody but not by anti-IL-1 beta antibody, indicating that IL-1 alpha is the predominant form in GCF. However, the IL-1 activity in GCF was unrelated to the number of IL-1 mRNA-expressing macrophages in the same gingival site where the GCF was obtained at the same time. The results suggest that macrophages in the connective tissue subjacent to the oral epithelium contribute to the production of IL-1 but those in connective tissue subjacent to the pocket epithelium play a different role in the generation of gingival inflammation.

Processing and presentation of intact hen egg-white lysozyme by dendritic cells

Dendritic cells in lymphoid tissues are of key importance as highly specialized antigen-presenting cells for the induction of T lymphocyte responses. Conflicting results have been published regarding antigen processing of intact proteins by dendritic cells. We now report that highly purified dendritic cells isolated from H-2k mouse spleens very efficiently generated immunogenic fragments of intact hen egg-white lysozyme (HEL) protein to present to an I-Ak-restricted T hybridoma cell line, specific for HEL peptide 46-61. Dendritic cells required 100 times less HEL protein than lipopolysaccharide-induced B cell blasts for effective presentation. Uptake of 125I-labeled HEL protein by dendritic cells and inhibition of presentation of HEL protein by chloroquine treatment was observed. This indicates an endocytotic process and the involvement of acidified compartments. Since the supernatant of dendritic cells, that were incubated with intact HEL protein, contained immunogenic fragments, further evidence for processing of HEL protein by dendritic cells was obtained. When HEL protein was covalently coupled to beads, dendritic cells were not able to ingest these beads, but could still process HEL protein for presentation. This suggests cell surface processing of HEL protein, although internalization of HEL protein released from the beads cannot be excluded. Taken together, these data show that H-2k dendritic cells are capable of processing and presenting intact HEL protein.

Induction of lymphocyte proliferation by antigen-pulsed human neutrophils

We have investigated whether purified antigen-pulsed human neutrophils can induce a proliferative response in purified resting blood lymphocytes. Neutrophils were pulsed with soluble tetanus toxoid (dose range 25-250 Lf/ml) and co-cultured with autologous lymphocytes that had been depleted of MHC class II expressing cells. The antigen-pulsed neutrophils induced an increase of lymphocyte proliferation which was dependent on the antigen dose and the neutrophil/lymphocyte ratios. Neutrophils were less potent than autologous monocytes in stimulating lymphocyte proliferation. Blocking with a monoclonal antibody to a common determinant of the human MHC class II complex failed to reduce the lymphoproliferative effects and allogenic antigen-pulsed neutrophils were also able to elicit lymphocyte proliferation similar to autologous neutrophils. We conclude that antigen-pulsed neutrophils are able to induce lymphocyte proliferation in a non-MHC-restricted fashion.

The in situ immune response of the rat after intraperitoneal depletion of macrophages by liposome-encapsulated dichloromethylene diphosphonate

This study concerns the contribution of peritoneal macrophages in vivo to local and systemic immune responses in the rat. Peritoneal macrophages as well as macrophages in the draining parathymic lymph nodes were selectively eliminated by intraperitoneal inoculation of dichloromethylene-diphosphonate-containing liposomes. This depletion resulted in an enhanced immune reaction to intraperitoneally administered trinitrophenyl keyhole limpet haemocyanin in the parathymic lymph nodes, as demonstrated by the higher numbers of specific anti-TNP antibody-forming cells in macrophage-depleted animals than in control animals from day 5 after immunization. The immune reaction peaked at day 7 and remained high until day 10. Specific antibody-forming cells were found occasionally in the mesenteric lymph nodes and spleen, but not in the mucosa of the gut or in the bronchus-associated lymphoid tissue. An elevated immune reaction found in parathymic lymph nodes associated with the depletion of local macrophages by liposome treatment indicates a regulatory role of peritoneal macrophages in local humoral immune response.

The in situ immune response in popliteal lymph nodes of mice after macrophage depletion. Differential effects of macrophages on thymus-dependent and thymus-independent immune responses

Mice were subcutaneously (SC) injected in the left hind footpad with dichloromethylene diphosphonate (Cl2MDP)-containing liposomes to eliminate macrophages lining the subcapsular sinus (SCS) and those in the medulla of draining popliteal lymph nodes (PLN). In order to study the effect of depletion of these macrophages on the in situ immune response in the PLN, liposome-treated mice were SC injected in the same footpad with thymus-independent (TI) type 1 antigen trinitrophenylated lipopolysaccharide (TNP-LPS), TI-type 2 antigen TNP-Ficoll or thymus-dependent (TD) antigen TNP-keyhole limpet haemocyanin (TNP-KLH). No major differences were observed in antibody-serum titers of liposome-treated and control animals. After primary as well as secondary immunization with the TD-antigen TNP-KLH, an increase in the number of antibody-forming cells (AFC) was found and the peak of response was delayed in the PLN of liposome-treated animals. Such differences were not observed with the TI-antigens. These results indicate that macrophages lining the SCS and those in the medulla of the PLN are not essential for the induction of an immune response. The positive effect of macrophage-depletion on the number of AFC may be explained by competition for the antigen by macrophages and other antigen-presenting cells.

Differences in responses of normal and rheumatoid arthritis peripheral blood T cells to synovial fluid and peripheral blood dendritic cells in allogeneic mixed leukocyte reactions

We examined the response of normal T cells to dendritic cells isolated from the synovial fluid (SF) of patients with either rheumatoid arthritis (RA) or seronegative spondylarthropathies (rheumatoid variants) and to dendritic cells from normal and RA peripheral blood (PB) in the allogeneic mixed leukocyte reaction. Despite the differences in the response kinetics, the stimulatory capacity of SF dendritic cells was similar to that of PB dendritic cells in a 7-day mixed leukocyte reaction. We also tested the responsiveness of normal and RA PB T cells to various allogeneic dendritic cells and found that RA PB T cells responded poorly to both rheumatoid variant SF dendritic cells and normal PB dendritic cells. However, when dendritic cells from RA SF were used as stimulators, the response of RA PB T cells was significantly greater than that of normal PB T cells (P less than 0.02). This difference in response was explained in part by a proliferation of the CD8 T cell subset. There was also a shift of low-intensity CD4+, CDw29+ cells to high-intensity CD4+, CDw29+ cells seen in RA PB T cells but not in normal PB T cells, by fluorescence-activated cell sorter analysis.

Antigen presenting cells

A great deal has been learned over the past few years regarding the molecular biology of antigen presentation. These discoveries have been possible in part because of acquisition of protein sequencing data regarding class I and class II MHC molecules and in part because of X-ray crystallographic analysis of the three-dimensional structures of these molecules. These discoveries have merged nicely with detailed immunologic studies delineating the 'minimal antigenic peptides' of complex protein antigens. All of these studies strongly confirm the belief that the antigen-specific interaction of T cells with antigen in the context of antigen presenting cells is exquisitely specific. The process of 'trimolecular complex' formation involves binding interactions between antigenic peptide, class I or class II MHC molecules and the antigen-specific T cell receptor. One of the key functions of antigen presenting cells involves the 'processing' of complex protein antigens so as to allow for the interaction of the 'minimal antigenic peptide' with the appropriate class I or class II MHC molecule. A substantial body of evidence now indicates that the interaction of processed antigenic peptides and class II MHC molecules involves a binding interaction with a significant binding affinity and a slow dissociation constant. In addition to antigen-specific binding interactions which govern antigen presentation, there are a variety of antigen-independent and MHC-independent factors which greatly augment the process of antigen presentation. Along with differences in antigen processing, these factors probably account for the qualitative and quantitative differences seen between the various cell types involved in antigen presentation. There may be a substantial amount of antigen which associates with the antigen presenting cell surface in an MHC-independent fashion associated with so-called 'non-MHC peptide binding structures'. However, if the trimolecular complex theory is to be satisfied, antigen bound to these structures ultimately must become associated with the MHC restricting element in order to effectively engage the antigen-specific T cell receptor. Antigen presenting cells differ in their sensitivity to lymphokines and inflammatory mediators which augment antigen presentation. In addition, antigen presenting cells differ in their capacity to secrete or express membrane-bound costimulatory molecules, such as interleukin 1. Finally, factors which promote the cellular adherence of antigen presenting cells with T cells greatly augment the process of antigen presentation.(ABSTRACT TRUNCATED AT 400 WORDS)

Maturation of the delayed-type hypersensitivity response in SJL mice: absence of effector cell induction

Immunization of young adult SJL mice (6 weeks of age) with a wide variety of particulate and soluble antigens does not elicit a delayed-type hypersensitivity (DTH) response. Young adult SJL lack a DTM response through 8 weeks of age but attain the mature adult level of responsiveness at 10 weeks of age. Nylon wool-enriched TDTH effectors and an antigen-specific T cell clone both elicited DTH responses when transferred into 6-week-old SJL. Thus, the cascade of events at the local site appears to be functionally intact in 6-week-old SJL. However, T cells from immunized 6-week-old SJL fail to transfer DTH responsiveness to naive 6-week-old SJL recipients unless macrophages from 12-week-old SJL supplemented the immunization. Thus, the unresponsiveness of 6-week-old SJL appears to be due to a lack of induction of TDTH effectors. In addition, SJL mice immunized at 6 weeks of age and challenged with antigen at the DTH responsive age of 12 weeks did not mount a DTH response. Immunized 6-week-old SJL, supplemented with macrophages from 12-week-old SJL, and 12-week-old SJL did respond to a second antigenic challenge when held for an equivalent 6-week period. Thus, 6-week-old SJL fail to induce TDTH effectors and to generate memory TDTH cells. Finally, antigen-pulsed macrophages from 12-week-old SJL transferred DTH responsiveness into naive 6-week and 12-week-old SJL recipients, while antigen-pulsed cells from 6-week donors were unable to transfer DTH responsiveness. These data indicate that the maturational deficit in the DTH responsiveness of 6-week-old SJL resides in the inability of macrophages to induce TDTH effectors.