Ken Shortman

Mouse and human dendritic cell subtypes

Dendritic cells (DCs) collect and process antigens for presentation to T cells, but there are many variations on this basic theme. DCs differ in the regulatory signals they transmit, directing T cells to different types of immune response or to tolerance. Although many DC subtypes arise from separate developmental pathways, their development and function are modulated by exogenous factors. Therefore, we must study the dynamics of the DC network in response to microbial invasion. Despite the difficulty of comparing the DC systems of humans and mice, recent work has revealed much common ground.

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.

Steady-state and inflammatory dendritic-cell development

The developmental pathways that lead to the production of antigen-presenting dendritic cells (DCs) are beginning to be understood. These are the last of the pathways of haematopoiesis to be mapped. The existence of many specialized subtypes of DC has complicated this endeavour, as has the need to distinguish the DCs formed in steady state from those produced during an inflammatory response. Here we review studies that lead to the concept that different types of DC develop through different branches of haematopoietic pathways that involve different immediate precursor cells. Furthermore, these studies show that many individual tissues generate their own DCs locally, from a reservoir of immediate DC precursors, rather than depending on a continuous flux of DCs from the bone marrow.

CD4 and CD8 Expression by Dendritic Cell Subtypes in Mouse Thymus and Spleen

The dendritic cells (DC) of mouse spleen and thymus were examined for expression of CD4 and CD8. Provided care was taken to avoid selective extraction or selective depletion of DC subpopulations, three main types of DC were detected in mouse spleen: a major new population of CD4+8− DEC-205low CD11bhigh DC, together with the previously described CD4−8− DEC-205low CD11bhigh DC and CD4−8αα+ DEC-205high CD11blow DC. The CD4 on the surface of the CD4+ splenic DC subpopulation was produced by the DC themselves, and CD4 RNA transcripts were present. Likewise, the CD8α on the surface of the splenic CD8+ DC was shown to be a product of the DC themselves, in agreement with earlier evidence. All three spleen DC types would be considered as mature, based on expression of CD80, CD86, and CD40 as well as on T cell stimulating function. Mouse thymuses appeared to contain two DC types; both were DEC-205highCD11blow, but they differed in the level of CD8αα expression. However, as well as this authenticated marker expression, immunofluorescent staining was also found to reflect a series of artifacts, due to the autofluorescence of contaminating cells and due to pickup of CD4 and CD8αβ. By constructing mice chimeric for the hemopoietic lineages using mixtures of wild-type bone marrow with CD4null or CD8αnull bone marrow, a marked pickup by thymic DC of Ags derived from thymocytes was demonstrated.

Cross-presentation of viral and self antigens by skin-derived CD103 + dendritic cells

Skin-derived dendritic cells (DCs) include Langerhans cells, classical dermal DCs and a langerin-positive CD103+ dermal subset. We examined their involvement in the presentation of skin-associated viral and self antigens. Only the CD103+ subset efficiently presented antigens of herpes simplex virus type 1 to naive CD8+ T cells, although all subsets presented these antigens to CD4+ T cells. This showed that CD103+ DCs were the migratory subset most efficient at processing viral antigens into the major histocompatibility complex class I pathway, potentially through cross-presentation. This was supported by data showing only CD103+ DCs efficiently cross-presented skin-derived self antigens. This indicates CD103+ DCs are the main migratory subtype able to cross-present viral and self antigens, which identifies another level of specialization for skin DCs.

Cutting edge: intravenous soluble antigen is presented to CD4 T cells by CD8- dendritic cells, but cross-presented to CD8 T cells by CD8+ dendritic cells.

Mouse spleen contains three distinct mature dendritic cell (DC) populations (CD4+8−, CD4−8−, and CD4−8+) which retain a capacity to take up particulate and soluble Ags. Although the three splenic DC subtypes showed similar uptake of injected soluble OVA, they differed markedly in their capacity to present this Ag and activate proliferation in OVA-specific CD4 or CD8 T cells. For class II MHC-restricted presentation to CD4 T cells, the CD8− DC subtypes were more efficient, but for class I MHC-restricted presentation to CD8 T cells, the CD8+ DC subtype was far more effective. This differential persisted when the DC were activated with LPS. The CD8+ DC are therefore specialized for in vivo cross-presentation of exogenous soluble Ags into the class I MHC presentation pathway.

Differential Production of IL-12, IFN-α, and IFN-γ by Mouse Dendritic Cell Subsets

Dendritic cells (DC) not only stimulate T cells effectively but are also producers of cytokines that have important immune regulatory functions. In this study we have extended information on the functional differences between DC subpopulations to include differences in the production of the major immune-directing cytokines IL-12, IFN-α, and IFN-γ. Splenic CD4−8+ DC were identified as the major IL-12 producers in response to microbiological or T cell stimuli when compared with splenic CD4−8− or CD4+8− DC; however, all three subsets of DC showed similar IL-12 regulation and responded with increased IL-12 p70 production if IL-4 was present during stimulation. High level CD8 expression also correlated with extent of IL-12 production for DC isolated from thymus and lymph nodes. By using gene knockout mice we ruled out any role for CD8α itself, or of priming by T cells, on the superior IL-12-producing capacity of the CD8+ DC. Additionally, CD8+ DC were identified as the major producers of IFN-α compared with the two CD8− DC subsets, a finding that suggests similarity to the human plasmacytoid DC lineage. In contrast, the CD4−8− DC produced much more IFN-γ than the CD4−8+ or the CD4+8− DC under all conditions tested.

The CD8alpha(+) dendritic cell is responsible for inducing peripheral self-tolerance to tissue-associated antigens.

We previously described a mechanism for the maintenance of peripheral self-tolerance. This involves the cross-presentation of tissue-associated antigens by a bone marrow–derived cell type that stimulates the proliferation and ultimate deletion of self-reactive CD8 T cells. This process has been referred to as cross-tolerance. Here, we characterize the elusive cell type responsible for inducing cross-tolerance as a CD8α+ dendritic cell (DC). To achieve this aim, transgenic mice were generated expressing yellow fluorescent protein (YFP) linked to CTL epitopes for ovalbumin and glycoprotein B (gB) of herpes simplex virus under the rat insulin promoter (RIP). Although tracking of YFP was inconclusive, the use of a highly sensitive gB-specific hybridoma that produced β-galactosidase on encounter with antigen, enabled detection of antigen presentation by cells isolated from the pancreatic lymph node. This showed that a CD11c+CD8α+ cell was responsible for cross-tolerance, the same DC subset as previously implicated in cross-priming. These data indicate that CD8α+ DCs play a critical role in both tolerance and immunity to cell-associated antigens, providing a potential mechanism by which cytotoxic T lymphocyte can be immunized to viral antigens while maintaining tolerance to self.

The Dendritic Cell Populations of Mouse Lymph Nodes

The dendritic cells (DC) of mouse lymph nodes (LN) were isolated, analyzed for surface markers, and compared with those of spleen. Low to moderate staining of LN DC for CD4 and low staining for CD8 was shown to be attributable to pickup of these markers from T cells. Excluding this artifact, five LN DC subsets could be delineated. They included the three populations found in spleen (CD4+8−DEC-205−, CD4−8−DEC-205−, CD4−8+DEC-205+), although the CD4-expressing DC were of low incidence. LN DC included two additional populations, characterized by relatively low expression of CD8 but moderate or high expression of DEC-205. Both appeared among the DC migrating out of skin into LN, but only one was restricted to skin-draining LN and was identified as the mature form of epidermal Langerhans cells (LC). The putative LC-derived DC displayed the following properties: large size; high levels of class II MHC, which persisted to some extent even in CIITA null mice; expression of very high levels of DEC-205 and of CD40; expression of many myeloid surface markers; and no expression of CD4 and only low to moderate expression of CD8. The putative LC-derived DC among skin emigrants and in LN also showed strong intracellular staining of langerin.

RelB Is Essential for the Development of Myeloid-Related CD8α− Dendritic Cells but Not of Lymphoid-Related CD8α+ Dendritic Cells

The transcription factor RelB had been shown to be important for dendritic cell (DC) development, but the type of DC involved was not clear. Here, we report that RelB mRNA is expressed strongly in CD8alpha- DEC-205- DC but only weakly in CD8alpha+ DEC-205+ DC. In addition, CD8alpha+ DEC-205+ DC are present and functional in RelB null mice, the DC deficiency being mainly in the CD8alpha- DEC-205- population. By constructing bone-marrow chimeric mice, we demonstrate that the partial deficiency in RelB null thymic DC is a secondary effect of disrupted thymic architecture. However, the deficiency in splenic CD8alpha- DEC-205- DC is a direct, stem cell intrinsic effect of the RelB mutation. Thus, RelB selectively regulates a myeloid-related DC lineage.