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Substantial progress has been made over the last several years in the development of protocols for the isolation of large numbers of dendritic cells (DCs) from different tissues and their short-term culture. Indeed, several stable DC lines and clones have been established from various tissues of mice and humans, providing useful experimental tools for studying the biology of DCs at both molecular and biochemical levels and for the establishment of new DC-based immunotherapies. In this chapter, we will describe the development of long-term DC lines that maintain the growth factor dependence and their immature functional state, thus providing a unique opportunity to study the mechanisms of the initiation of the immune response to infectious agents

A mimetic of Lipid A with a -N(OMe) glycosidic linkage, four linear C-14 hydrophobic chains and without phosphate groups has been prepared together with its b-O-linked analogue. Both these molecules were active in inhibiting the inflammatory action of Escherichia coli lipid A on MT2 macrophages in a dose-dependent manner, while they were completely devoid of inflam- matory activity.

Recognition of pathogen-associated molecular patterns (PAMP) influences the response of dendritic cells (DC) and therefore development of innate and adaptive immunity. Different forms of Leishmania mexicana have distinct effects on DC, with promastigotes and amastigotes being activating and apparently neutral, respectively. We investigated whether stage-specific differences in surface composition might account for these distinct effects. Amastigotes and promastigotes lacking the lpg1 gene needed for lipophosphoglycan (LPG) biosynthesis could not activate DC in vitro. Genome-wide transcriptional profiling of DC infected with wild-type or mutant promastigotes or wild-type amastigotes revealed that wild-type promastigotes induce an inflammatory signature that is lacking in DC exposed to the other parasite forms. The proinflammatory response pattern was partly recovered by reconstitution of lpg1 expression in lpg1-/- parasites, and exposure to purified LPG increased the expression of MHC class II and CD86 on DC. Infection with wild-type but not lpg1-/- promastigotes increased the number of activated DC in draining lymph nodes, and this was correlated with lower early parasite burdens in wild-type-infected animals. These in vivo and in vitro results suggest an LPG-dependent activation of DC that contributes to host defense and agree with the notion that the parasites evolved under immune pressure to down-regulate PAMP expression in mammalian hosts.

The immune system has developed mechanisms to detect and initiate responses to a continual barrage of immunological challenges. Dendritic cells (DC) play a major role as immune surveillance agents. To accomplish this function, DC are equipped with highly efficient mechanisms to detect pathogens, to capture, process and present antigens, and to initiate T-cell responses. The recognition of molecular signatures of potential pathogens is accomplished by membrane receptor of the toll-like family (TLRs), which activates DC, leading to the initiation of adaptive immunity. High-density DNA microarray analysis of host gene expression provides a powerful method of examining microbial pathogens from a novel perspective. The ability to survey the responses of a large subset of the host genome, and to find patterns among the profiles from many different microorganisms and hosts, allows fundamental questions to be addressed about the basis of pathogen recognition, the features of the interaction between host and pathogen and the mechanisms of host defense and microbial virulence. The biological insights thus gained are likely to lead to major shifts in our approach to the diagnosis, treatment, assessment of prognosis, and prevention in many types of infectious diseases within a decade.