Derek N. J. Hart

Nomenclature of monocytes and dendritic cells in blood

Monocytes and cells of the dendritic cell lineage circulate in blood and eventually migrate into tissue where they further mature and serve various functions, most notably in immune defense. Over recent years these cells have been characterized in detail with the use of cell surface markers and flow cytometry, and subpopulations have been described. The present document proposes a nomenclature for these cells and defines 3 types of monocytes (classical, intermediate, and nonclassical monocytes) and 3 types of dendritic cells (plasmacytoid and 2 types of myeloid dendritic cells) in human and in mouse blood. This classification has been approved by the Nomenclature Committee of the International Union of Immunological Societies, and we are convinced that it will facilitate communication among experts and in the wider scientific community.

Human CD141+ (BDCA-3)+ dendritic cells (DCs) represent a unique myeloid DC subset that cross-presents necrotic cell antigens

The characterization of human dendritic cell (DC) subsets is essential for the design of new vaccines. We report the first detailed functional analysis of the human CD141+ DC subset. CD141+ DCs are found in human lymph nodes, bone marrow, tonsil, and blood, and the latter proved to be the best source of highly purified cells for functional analysis. They are characterized by high expression of toll-like receptor 3, production of IL-12p70 and IFN-β, and superior capacity to induce T helper 1 cell responses, when compared with the more commonly studied CD1c+ DC subset. Polyinosine-polycytidylic acid (poly I:C)–activated CD141+ DCs have a superior capacity to cross-present soluble protein antigen (Ag) to CD8+ cytotoxic T lymphocytes than poly I:C–activated CD1c+ DCs. Importantly, CD141+ DCs, but not CD1c+ DCs, were endowed with the capacity to cross-present viral Ag after their uptake of necrotic virus-infected cells. These findings establish the CD141+ DC subset as an important functionally distinct human DC subtype with characteristics similar to those of the mouse CD8α+ DC subset. The data demonstrate a role for CD141+ DCs in the induction of cytotoxic T lymphocyte responses and suggest that they may be the most relevant targets for vaccination against cancers, viruses, and other pathogens.

DISTRIBUTION AND QUANTITATION OF HLA-ABC AND DR (Ia) ANTIGENS ON HUMAN KIDNEY AND OTHER TISSUES

A quantitative estimation of the amounts of human Ia (HLA-DR) and HLA-ABC antigen on a variety of human tissues was performed. Monoclonal antibodies to species-common determinants of HLA-DR and HLA-ABC antigens were absorbed quantitatively with tissue homogenates and cell suspensions, and reassayed for residual activity in a radioimmunobinding assay. Kidney was found to carry 90% as much HLA-DR and 14% as much HLA-ABC antigen as spleen, while liver contained 19 and 9% as much, respectively. Small amounts of both antigens were found on heart; brain carried very little HLA-ABC and virtually no DR. Neither HLA-ABC nor DR was found on erythrocytes or reticulocytes. Of interest was our finding that a small subpopulation of thymocytes (10%) was HLA-DR positive. Platelets contained approximately 5% of the amount of HLA-ABC as spleen and undetectable quantities of HLA-DR, as expected. Chronic lymphatic leukemia (CLL) cells were found to carry 10% as much HLA-ABC and 33% as much DR antigen as spleen, while the values for bone marrow were 15 and 2%, respectively.

LOCALIZATION OF HLA-ABC AND DR ANTIGENS IN HUMAN KIDNEY

Monoclonal antibodies to human monomorphic class I and class II major histocompatibility complex (MHC) determinants have been used with immunofluorescence and immunoperoxidase techniques, to localize these antigens in normal human kidneys. HLA-DR antigen was located in the glomeruli (probably on endothelium as well as in the mesangium) and within the cells of cortical and medullary tubules. Dendritic cells in the renal inter-stitium stained brightly for the DR antigen and could be distinguished from the staining of capillary endothelium. The vascular endothelium of large vessels stained less densely for the HLA-DR antigen than for HLA-ABC antigens. The glomeruli stained intensely for the HLA-ABC antigens and diffuse staining of HLA-ABC antigens was also noted within renal tubular cells.

The fate of human Langerhans cells in hematopoietic stem cell transplantation.

Langerhans cells (LC) and other antigen-presenting cells are believed to be critical in initiating graft versus host responses that influence the outcome of allogeneic hematopoietic stem cell transplantation. However, their fate in humans is poorly understood. We have sought to define the effect of conditioning regimes and graft versus host disease (GVHD) on the survival of recipient LC and reconstitution of donor cells after transplant. Confocal microscopy of epidermal sheets shows that full intensity transplant (FIT) depletes LC more rapidly than reduced intensity transplant (RIT) at day 0, although the nadir is similar in both at 14–21 d. Recovery occurs rapidly within 40 d in the absence of acute GVHD, but is delayed beyond 100 d when GVHD is active. LC chimerism was determined in sex-mismatched transplants using a two-step Giemsa/fluorescence in situ hybridization assay on isolated cells. Acquisition of donor chimerism at 40 d is more rapid after FIT (97%) than RIT (36.5%), irrespective of blood myeloid engraftment. At 100 d, all transplants achieve at least 90% LC donor chimerism and over half achieve 100%. Complete donor chimerism is associated with prior acute cutaneous GVHD, suggesting a role for allogeneic T cells in promoting LC engraftment.

Major histocompatibility complex antigens in rat kidney, ureter, and bladder. Localization with monoclonal antibodies and demonstration of Ia-positive dendritic cells.

Monoclonal mouse xenoantibodies to the SD and part of the Ia antigen complex of the rat major histocompatibility complex (MHC) were raised, and used to localize MHC antigens on frozen sections of kidney, ureter, and bladder of the DA rat strain. The Ia antigens recognized by our monoclonal antibody were located almost entirely within the cells of some, probably the proximal, convoluted tubules of the kidney. The only other Ia-bearing structures were intensely Ia-positive dendritic cells found predominantly in the renal cortex and in the mucosal connective tissues of the ureter and bladder. The SD antigens were widely distributed in the kidney with a major portion again located within the tubular cells, although in the case of SD antigens all tubular cells, including those of the medulla, were positive. By far the brightest tubules were clusters in the outer medulla, probably representing the thick loops of Henle. The endothelium of arterioles, venules and glomerular and interstitial capillaries all stained very brightly for SD antigens. The glomerular mesangium and the interstitial connective tissues of the kidney, ureter, and bladder all gave diffuse positive staining for SD antigens. Transplantation studies established that the tubular Ia and SD antigens of the kidney are produced by the cells and are not in the process of excretion or reabsorption.

Characterization of interstitial dendritic cells in human liver

Sensitive immunofluorescence and immunoperoxidase techniques were used to test an extensive range of monoclonal antibodies for reactivity with Kupffer cells and interstitial dendritic cells (DCs) in cryostat-cut sections of human liver. Leucocytes with a dendritic cell morphology were identified with CD45 (antileucocyte common) reagents in portal tracts, predominantly around bile ducts, and these cells stained strongly for the HLA-DP, DQ, and DR antigens. Kupffer cells stained less intensely with anti-class-II reagents, particularly anti-HLA-DQ. The interstitial DCs expressed the LFA-1 antigen but failed to stain with CD11b, CD11c, and the defined T and B cell CD antibodies; nor did they stain with antibodies to FcR1, FcR11, FcRIII, or the C3b receptor. Of the myeloid monoclonal antibodies available from the 3rd Leucocyte Differentiation Antigen Workshop, only Y2/131, Ki-M7, Ki-M8, and a minority of CD14 antibodies stained DCs, whereas Kupffer cells showed a wider reactivity with antimacrophage antibodies including those of workshop groups 11, 15, 16, and other unique antibodies. A 2nd probable DC population was identified in the liver capsule that had a similar phenotype to portal interstitial DCs. Although some minor phenotypic differences between liver portal DCs and the phenotypes of Langerhans cells and isolated tonsil DCs were noted, our results support the view that there is a unique hemopoietic lineage of DCs. The presence of DCs, which stimulate strong allogeneic T cell responses, in the portal triads is consistent with the fact that the histologic changes of graft-versus-host disease seen in bone marrow transplantation and the lymphocytic infiltrate in a rejecting liver allograft occur predominantly in the periportal region.

The role of dendritic cells in the innate immune system

Dendritic cells (DCs) are bone-marrow-derived leucocytes that are specialised antigen-presenting cells capable of stimulating a primary T-lymphocyte response to specific antigen. In this chapter we discuss the role DCs play in the innate response acting as a critical link with the adaptive response and the influence of the innate response on dendritic cells.

The CD300 family of molecules are evolutionarily significant regulators of leukocyte functions

The CD300 glycoproteins are a family of cell surface molecules that modulate a diverse array of cell processes via their paired triggering and inhibitory receptor functions. Family members share a common evolutionary pathway and at least one member of the family has undergone significant positive selection, indicating their crucial value to the host. This review clarifies the occasionally confusing usage of nomenclature for the CD300 family and summarizes our current understanding of their genomics, expression and function. Their ability to fine tune leukocyte function and immune responses highlights several potential options to exploit the CD300 molecules as therapeutic targets in chronic inflammatory diseases, allergy and other disease states.

Dendritic Cells in Cancer Immunotherapy

Since their discovery, there has been significant progress in the understanding of dendritic cell (DC) biology. Their capacity for priming an immune response against pathogens and cancers has been exploited clinically. However, the objective responses obtained to date using DC cancer vaccines have been modest. Suboptimal DC preparations, limited tumor target antigens, and the essential need to initiate trials in immunocompromised patients with advanced disease, have all contributed to limited outcomes. The use of fully activated DCs, loaded with multiple, immunogenic, cancer-specific antigens, administered to patients with minimal residual disease and the manipulation of regulatory mechanisms underlying peripheral tolerance, may be the ingredients for future success.