Dendritic cells (DCs) are considered the most potent antigen-presenting cells (APCs), which directly prime or cross-prime MHC I-restricted cytotoxic T cells (CTLs). However, recent evidence suggests the existence of other, as-yet unidentified APCs also able to prime T cells. To identify those APCs, we used adenoviral (rAd) vectors, which do not infect DCs but selectively accumulate in CD169 + macrophages (MPs). In mice that lack DCs, infection of CD169 + MPs was sufficient to prime CTLs specific for all epitopes tested. In contrast, CTL responses relying exclusively on cross-presenting DCs were biased to selected strong MHC I-binding peptides only. When both DCs and MPs were absent, no CTL responses could be elicited. Therefore, CD169+ MPs can be considered APCs that significantly contribute to CTL responses. + T cells (4). In contrast, MPs are considered cells of the innate immune system that limit pathogen spread by phagocytosis and degradation. They are positioned at strategically important entry points, such as the subcapsular sinus of lymph nodes and the marginal zone and red pulp areas of the spleen, where they capture and filter pathogens (5). Along with producing type I IFN (6), CD169+ marginal zone metallophilic MPs allow restricted replication of captured virus to increase the local availability of viral Ag (7) for transfer to B cells for humoral responses (8) and to DCs for cross-priming of CD8 + T cells (9). Participation of MPs in T-cell priming is thought to be restricted to Ag acquisition, amplification, and redistribution.Analyzing MP functions in vivo is difficult; genetic models, such as the CD11c-diphteria toxin (DT) receptor (DTR) transgenic mice (2), cannot make the distinction, because both DCs and monocytes/MPs are equally deleted on DT treatment (10, 11). Recent results with mice lacking CD169 + MPs suggest the role of these MPs in cross-priming of CD8 + T cells specific for the cell-associated model Ag ovalbumin (OVA) in lymph nodes (12). These findings are in contrast with another study in which MPs were unable to cross-present soluble OVA protein in mice lacking DCs (11). Although cross-presentation by DCs is now thought to allow priming of cytotoxic T-cell responses to exogenous tumor or viral Ag (4), the importance of cross-presentation in vivo has been a matter of intense debate over the last decade (13). Although this debate remains unresolved, cross-presentation has been considered then and now to be an exception rather than a rule (14,15).To determine the roles of MPs and DCs, we used a mouse model that specifically lacks DCs but conserves all subpopulations of MPs. We show that the presence of directly infected CD169 + MPs is sufficient to prime CTLs, including those recognizing epitopes not covered by cross-presenting DCs. In contrast, when only DCs cross-prime CTLs without the participation of MPs, the CTL repertoire is incomplete and biased toward the few peptides that interact strongly with MHCI. Our data demonstrate a division of labor between CD169 + MPs and DCs in situati...

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Normal human keratinocytes show chemotactic behavior towards interleukin‐8 (IL‐8). Under physiological conditions this cylokine seems to be present in an equilibrium between monomeric and dimeric forms, as indicated by Western blotting data. Radioligand binding studies suggest that keratinocyte chemotaxis is mediated by receptors specific for IL‐8 dimers. IL‐8 rcceptor‐specific mRNA can be detected in a keratinocyte cell line by polymerase chain reaction.

Gene gun-mediated DNA immunization is a powerful mode of vaccination against infectious diseases and tumors. Many studies have identified dendritic cells (DC) as the central players in inducing immunity upon biolistic DNA vaccination; however, none of these studies directly quantify DC-mediated responses in comparison with immunity triggered by all Ag- and MHC-expressing cells. In this study we use two different approaches to decipher the relative role of DC vs other cell types in gene gun-induced immunity. First, we directly compared the immunization efficacy of different DNA constructs, which allow Ag expression ubiquitously (CMV promoter) or specifically in DC (CD11c promoter) and would encode either for soluble or membrane bound forms of Ag. Second, we immunized transgenic mice in which only DC can present MHC-restricted Ag, and directly compared the magnitudes of CTL activation with those obtained in wild-type mice. Surprisingly, our combined data suggest that, although DC-specific Ag expression is sufficient to induce humoral responses, DC alone cannot trigger optimal CD4 and CD8 T cell responses upon gene gun vaccination. Therefore, we conclude that DC alone are insufficient to mediate optimal induction of T cell immunity upon gene gun DNA vaccination and that broad Ag expression rather than DC-restricted approaches are necessary for induction of complete immune responses.

DCs very potently activate CD8+ T cells specific for viral peptides bound to MHC class I molecules. However, many viruses have evolved immune evasion mechanisms, which inactivate infected DCs and might reduce priming of T cells. Then MHC class I cross-presentation of exogenous viral Ag by non-infected DCs may become crucial to assure CD8+ T cell responses. Although many vital functions of infected DCs are inhibited in vitro by many different viruses, the contributions of cross-presentation to T cell immunity when confronted with viral immune inactivation in vivo has not been demonstrated up to now, and remains controversial. Here we show that priming of Herpes Simplex Virus (HSV)-, but not murine cytomegalovirus (mCMV)-specific CD8+ T cells was severely reduced in mice with a DC-specific cross-presentation deficiency. In contrast, while CD8+ T cell responses to mutant HSV, which lacks crucial inhibitory genes, also depended on CD8α+ DCs, they were independent of cross-presentation. Therefore HSV-specific CTL-responses entirely depend on the CD8α+ DC subset, which present via direct or cross-presentation mechanisms depending on the immune evasion equipment of virus. Our data establish the contribution of cross-presentation to counteract viral immune evasion mechanisms in some, but not all viruses.