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To migrate efficiently through the interstitium, dendritic cells (DCs) constantly adapt their shape to the given structure of the extracellular matrix and follow the path of least resistance. It is known that this amoeboid migration of DCs requires Cdc42, yet the upstream regulators critical for localization and activation of Cdc42 remain to be determined. Mutations of DOCK8, a member of the atypical guanine nucleotide exchange factor family, causes combined immunodeficiency in humans.In the present study, we show that DOCK8 is a Cdc42-specific guanine nucleotide exchange factor that is critical for interstitial DC migration. By generating the knockout mice, we found that in the absence of DOCK8, DCs failed to accumulate in the lymph node parenchyma for T-cell priming. Although DOCK8-deficient DCs migrated normally on 2-dimensional surfaces, DOCK8 was required for DCs to crawl within 3-dimensional fibrillar networks and to transmigrate through the subcapsular sinus floor. This function of DOCK8 depended on the DHR-2 domain mediating Cdc42 activation. DOCK8 deficiency did not affect global Cdc42 activity. However, Cdc42 activation at the leading edge membrane was impaired in DOCK8-deficient DCs, resulting in a severe defect in amoeboid polarization and migration. Therefore, DOCK8 regulates interstitial DC migration by controlling Cdc42 activity spatially. (Blood. 2012; 119(19):4451-4461) IntroductionDendritic cells (DCs) are specialized APCs that play a critical role in the initiation of adaptive immune responses. 1 After antigen exposure, DCs phagocytose antigens in peripheral tissues and migrate via the afferent lymphatic vessels into the draining lymph nodes (LNs) to stimulate T cells. 2,3 During this process, DCs switch their sessile sampling behavior to a highly migratory one, which is characterized by the acquisition of a polarized morphology and increased expression of the chemokine receptor CCR7. Whereas CCR7 signals guide DCs to the LN parenchyma, 4 DCs must pass through a 3-dimensional (3D) interstitial space composed of fibrillar extracellular matrix (ECM) before reaching their destination. To perform this task efficiently, DCs constantly adapt their shape to the given structure of the interstitial ECM and follow the path of least resistance. 5 This amoeboid migration of DCs occurs independently of adhesion to specific substrates and ECM degradation, 6,7 yet its regulatory mechanisms are poorly understood.Cdc42 is a member of the Rho family of small GTPases that function as molecular "switches" by cycling between GDP-bound inactive states and GTP-bound active states. 8 Cdc42 exists in the cytosol in the GDP-bound form and is recruited to membranes, where its GDP is exchanged for GTP because of the action of one or more guanine nucleotide exchange factors (GEFs). Once activated, Cdc42 binds to multiple effector molecules and regulates various cellular functions. Cdc42 is known to act as a master regulator of cell polarity in eukaryotic organisms ranging from yeasts to humans. 8 In addition, a recent stu...

When developing malaria vaccines, the most crucial step is to elucidate the mechanisms involved in protective immunity against the parasites. We found that CD8+ T cells contribute to protective immunity against infection with blood‐stage parasites of Plasmodium yoelii. Infection of C57BL/6 mice with P. yoelii 17XL was lethal, while all mice infected with a low‐virulence strain of the parasite 17XNL acquired complete resistance against re‐infection with P. yoelii 17XL. However, the host mice transferred with CD8+ T cells from mice primed only with P. yoelii 17XNL failed to acquire protective immunity. On the other hand, the irradiated host mice were completely resistant to P. yoelii 17XL infection, showing no grade of parasitemia when adoptively transferred with CD8+ T cells from immune mice that survived infection with both P. yoelii XNL and, subsequently, P. yoelii 17XL. These protective CD8+ T cells from immune WT mice had the potential to generate IFN‐γ, perforin (PFN) and granzyme B. When mice deficient in IFN‐γ were used as donor mice for CD8+ T cells, protective immunity in the host mice was fully abrogated, and the immunity was profoundly attenuated in PFN‐deficient mice. Thus, CD8+ T cells producing IFN‐γ and PFN appear to be involved in protective immunity against infection with blood‐stage malaria.

Malaria is still a life-threatening infectious disease that continues to produce 2 million deaths annually. Malaria parasites have acquired immune escape mechanisms and prevent the development of sterile immunity. Regulatory T cells (Tregs) have been reported to contribute to immune evasion during malaria in mice and humans, suggesting that activating Tregs is one of the mechanisms by which malaria parasites subvert host immune systems. However, little is known about how these parasites activate Tregs. We herein show that TLR9 signaling to dendritic cells (DCs) is crucial for activation of Tregs. Infection of mice with the rodent malaria parasite Plasmodium yoelii activates Tregs, leading to enhancement of their suppressive function. In vitro activation of Tregs requires the interaction of DCs with parasites in a TLR9-dependent manner. Furthermore, TLR9−/− mice are partially resistant to lethal infection, and this is associated with impaired activation of Tregs and subsequent development of effector T cells. Thus, malaria parasites require TLR9 to activate Tregs for immune escape.