Absence of a microbiome in the midgut trunk of six representative Crustacea

It has become a common expectation for an animal’s guts to be a site for bacterial symbiosis, which may play a role in influencing various aspects of physiology including digestion and immune responses. The presence of a microbiome in the digestive tracts of crustaceans has been demonstrated in the past using molecular techniques and has encouraged manipulations including probiotics to enhance growth rates in cultured species. We suggest, however, that bacteria are restricted to the lumen of the gut and separated from the epithelium by the peritrophic matrix, which prevents their establishment as a permanent component of the gut. The peritrophic matrix, found in most arthropods, is a chitinous sheet containing accessory molecules, and is continuously formed by delamination from the epithelium of the midgut such that the actual surface is constantly being cleaned. The lifted layer then surrounds ingested materials, including microbes, in an impenetrable wrapper compartmentalizing digestive and immune functions. The ectoperitrophic space, lying between the peritrophic matrix and the epithelium, was examined in six species representatives of six groups of crustaceans (Branchiopoda, Amphipoda, Copepoda, and Decapoda) for the presence of microbes using light and transmission electron microscopy as well as fluorescent probes for bacteria. The results suggest that a microbiome is lacking in several common groups of crustaceans.

Resistance of Hematopoietic Stem Cells Lacking the KIR Ligand to Autologous NK Cell Attacks in Patients with Acquired Aplastic Anemia

Normal blood cells, including hematopoietic stem cells (HSCs), express KIR ligands (KIR-Ls) to protect themselves from an autologous NK cell attack, and malignant cells lacking KIR-Ls elicit NK cell-mediated killing of themselves. This missing-self mechanism is believed to play an important role in the elimination of malignant cells. However, the mechanisms underlying the killing of KIR-L-lacking malignant cells by NK cells remain unclear due to the heterogeneity of tumor cells in terms of their proliferative capacity, and also because other accessory molecules may be involved in the NK cell attacks, in addition to KIR-Ls. This makes it difficult to clarify the interaction between NK cells and KIR-L-lacking target cells. The lack of class I HLA occurs not only in malignant blood cells, but also in the normal leukocytes of patients with acquired aplastic anemia (AA). These HLA-lacking leukocytes, detectable in 13% of patients with AA, are derived from HSCs that undergo copy number neutral loss of heterozygosity of the short arm of chromosome 6 (6pLOH), and thereby escape the cytotoxic T-cell (CTL) attack against HSCs. The 6pLOH may involve KIR-L loss in some patients, leading to a change in the susceptibility of the affected HSCs to NK cell-mediated killing. Unlike malignant cells, HLA-lacking leukocytes are essentially the same as the wild-type leukocytes, except for the HLA expression. Studying 6pLOH (+) AA patients with leukocytes lacking KIR-Ls should therefore be useful for clarifying the roles of KIR-Ls and other accessory molecules in the target cell killing by NK cells. Screening of 389 patients with AA using flow cytometry and a SNP array analysis revealed that there were HLA-A allele-lacking leukocytes in 60 (15.4%) patients, which included 36 C1/C2 and 24 Bw4/Bw6 heterozygotes. Unexpectedly, a lack of KIR-Ls as a result of 6pUPD was found in five patients (13.9%, C1 missing in two and C2 missing in three) of the 36 C1/C2 heterozygotes and in five (20.8%) of the 24 Bw4/Bw6 heterozygotes, although the proportion of patients lacking a KIR-L-containing haplotype (20.8%) was significantly lower than that of patients lacking a haplotype that did not contain KIR-Ls (79.2%). Moreover, the median percentage of HLA-A-lacking granulocytes in the 10 patients who lacked a KIR-L-containing haplotype (12.4%, 0.44%-50.3%) was significantly lower than that (55.3%, 1.4%-99.4%) in the 26 patients who lacked a haplotype that did not contain KIR-Ls, suggesting that the HSCs lacking KIR-Ls or their progenies are susceptible to autologous NK cells to some extent, but are not eliminated completely. To clarify the mechanisms underlying the HSC resistance to NK cells, we determined the KIR gene repertoire and the haplotype of seven patients whose 6pLOH(+) leukocytes were lacking a KIR-L-containing haplotype. All patients possessed inhibitory KIR genes responsive to corresponding KIR-Ls, a finding that negates the possibility that NK cells failed to undergo licensing in these patients. Although the frequency of the KIR-B haplotype, a haplotype associated with a higher cytotoxic function of NK cells, in the seven patients was lower (14%) than that in Japanese healthy individuals (40.1%), two patients possessed the KIR-B haplotype. Phenotypic analyses of the NK cell subsets defined by anti-2DL1, anti-2DL2/2DL3 and anti-3DL1 antibodies showed that all seven patients had a similar percentage of the eight different NK cell subsets, which included 0.5 to 8% of effector NK cells capable of killing leukocytes lacking corresponding KIR-Ls. The expression level of HLA-E was comparable between HLA-A-lacking and HLA-A-retaining monocytes. The expression of NKG2A on the effector NK cells was also comparable to that of the other NK cell subsets in the 6pLOH(+) patients. Our study demonstrated, for the first time, that HSCs lacking KIR-Ls can evade autologous NK cell attack through an as yet unknown mechanism(s) and can continue to generate blood cells in patients with AA. Disclosures No relevant conflicts of interest to declare.

mTOR Activation Promotes Plasma Cell Differentiation and Bypasses XBP-1 for Immunoglobulin Secretion

Plasma cells (PCs) are responsible for the secretion of antibodies. The development of fully functional PCs relies on the activation of the inositol-requiring enzyme 1/X-box binding protein 1 (IRE1/XBP-1) arm of the unfolded protein response (UPR). XBP-1-deficient PCs secrete antibodies poorly and exhibit distensions of the endoplasmic reticulum (ER). The kinase mammalian target of rapamycin (mTOR) promotes anabolic activities and is negatively regulated by the tuberous sclerosis complex (TSC). Deletion of TSC1 renders mTOR hyperactive. To explore the relationship between mTOR and the UPR in PC development and function, mice with conditional deletions of XBP-1 and/or TSC1 in their B cell lineage were generated. Deletion of TSC1 enhanced Ig synthesis and promoted differentiation into PCs independently of XBP-1, as evidenced by comparison of TSC1/XBP-1 double-knockout (DKO) PCs to XBP-1 knockout (KO) PCs. The typical morphological abnormalities of the ER in XBP-1 KO PCs were alleviated in the DKO PCs. Expression profiling identified the glycoprotein Ly6C as an mTOR target. Ly6C expression contributed to the enhanced Ig secretion from DKO PCs. Our data reveal a functional overlap between mTOR and the UPR in promoting PC development. In addition to the classical mTOR role in promoting protein synthesis, the mechanism entails transcription regulation of accessory molecules, such as Ly6C.

Sex-Associated Expression of Co-Stimulatory Molecules CD80, CD86, and Accessory Molecules, PDL-1, PDL-2 and MHC-II, in F480+ Macrophages during Murine Cysticercosis

Macrophages are critically involved in the interaction betweenT. crassicepsand the murine host immune system. Also, a strong gender-associated susceptibility to murine cysticercosis has been reported. Here, we examined the sex-associated expression of molecules MHC-II, CD80, CD86, PD-L1, and PD-L2 on peritoneal F4/80himacrophages of BALB/c mice infected withTaenia crassiceps. Peritoneal macrophages from both sexes of mice were exposed toT. crassicepstotal extract (TcEx). BALB/c Females mice recruit higher number of macrophages to the peritoneum. Macrophages from infected animals show increased expression of PDL2 and CD80 that was dependent from the sex of the host. These findings suggest that macrophage recruitment at early time points duringT. crassicepsinfection is a possible mechanism that underlies the differential sex-associated susceptibility displayed by the mouse gender.

Rab35 Mediates Transport of Cdc42 and Rac1 to the Plasma Membrane during Phagocytosis

ABSTRACT Phagocytosis of invading microbes requires dynamic rearrangement of the plasma membrane and its associated cytoskeletal actin network. The polarization of Cdc42 and Rac1 Rho GTPases to the site of plasma membrane protrusion is responsible for the remodeling of actin structures. However, the mechanism of Rho GTPase recruitment to these sites and the identities of accessory molecules involved in this process are not well understood. In this study, we uncovered several new components involved in innate immunity in Drosophila melanogaster. Our data demonstrate that Rab35 is a regulator of vesicle transport required specifically for phagocytosis. Moreover, recruitment of Cdc42 and Rac1 to the sites of filopodium and lamellipodium formation is Rab35 dependent and occurs by way of microtubule tracks. These results implicate Rab35 as the immune cell-specific regulator of vesicle transport within the actin-remodeling complex.