Shiga toxin (Stx)-producing Escherichia coli O157:H7 is the causative agent of a severe food-borne illness complicated by diarrhea-associated hemolytic uremic syndrome (D + HUS). The study by Morigi et al. (p. 172) focused on how Stx-induced complement (C) activation affected glomerular thrombus formation. Using the human microvascular endothelial cell line HMEC-1 under flow conditions, the authors observed that Stx bound to P-selectin and activated C via the alternative pathway. Interestingly, the toxin further enhanced P-selectin expression, while reducing thrombomodulin, and caused C deposition and thrombus formation through the generation of C3a. The in vitro findings were validated in a murine HUS model. Compared with control mice, mice co-injected with Stx2 and LPS demonstrated severely impaired renal function with increased expression of P-selectin in glomeruli and excessive C3 deposits. Treatment with a specific anti–P-selectin Ab reduced C3 deposits, and administration of C3aR antagonist significantly reduced fibrin(ogen) deposition. After Stx2 + LPS treatment, factor B-deficient (Bf−/−) mice, which are unable to activate C via the alternative pathway, showed protection against renal dysfunction, when compared with wild-type mice. These findings on the role of C3a in Stx-induced thrombogenesis may potentially support the use of C3a inhibitors in the treatment of D + HUS.
Mycobacterium tuberculosis infection is initiated by the phagocytosis of bacteria by alveolar macrophages (AMs). Nonpathogenic M. tuberculosis bacteria are then degraded upon fusion of the phagosomal compartment with lysosomes. These events take place in the alveoli of the lung, a microenvironment containing enzymatic secretions from a variety of cells. Arcos et al. (p. 372) identified several hydrolases, including alkaline and acid phosphatases, and nonspecific esterases in human alveolar lining fluid (ALF). The authors studied the effect of physiological concentrations of these enzymes and AM lysates on the M. tuberculosis cellular envelope. They found that even short-term treatments reduced the envelope content of molecules critical for bacteria recognition by AMs and for disease pathogenesis (e.g., mannose-capped lipoarabinomannan and trehalosedimycolate). The envelope changes correlated with a decrease in AM phagocytosis and early bacterial intracellular growth, and induction of proinflammatory responses with release of TNF-α from AMs, as well as an enhancement of phagosome–lysosome fusion. This study thus provides new insights into the interaction of M. tuberculosis with the host at the early stages of infection and suggests a critical role for ALF in the pathogenesis of tuberculosis.
Sweet Dreams, Lasting Memory
It is known that sleep positively influences immune functions. Lange et al. (p. 283) examined the impact of sleep deprivation on the human immune response to vaccination. Study participants received anti-hepatitis A and B vaccination and were either kept awake or allowed regular sleep the night after each of the three inoculations. Immune responses were evaluated at various times during and after the vaccination cycle. Vaccination induced a robust hepatitis A-specific Th response that peaked at 2–4 weeks after the last injection in both groups. However, sleep generally boosted specific immune responses, with a significant increase in the frequency of IFN-γ+CD40L+ Th cells, which correlated with a significant rise in IgG1 levels. Enhanced immune responses against both hepatitis A and B Ags were observed. Of interest, the boosting effect was long lived and noticeable 1 year after initial vaccination. Moreover, the authors found a strong association between Th cell percentage and the time spent in slow-wave sleep stage 4. Analysis of the endocrine milieu present in the participants’ blood revealed that, compared with wakefulness, sleep increased growth hormone and prolactin levels but decreased cortisol and catecholamine levels. This study indicates that sleep has a beneficial effect on vaccination-induced T and B cell responses.
The mechanisms responsible for drug hypersensitivity are still unclear but could involve drug-mediated immune stimulation through the formation of haptens that modify endogenous proteins. Using novel mass spectrometric techniques, Whitaker et al. (p. 200) characterized haptenic adducts formed on human serum albumin by piperacillin, an antibiotic widely used by patients with cystic fibrosis. The authors found that when albumin was exposed to the drug in vitro or was isolated from patients undergoing therapy, four lysines (residues 190, 195, 432, and 541) were preferentially modified by two main forms of piperacillin haptens: cyclized and hydrolyzed haptens. A series of functional assays were then undertaken to study the relationship between the chemistry of drug-induced protein modification and immunogenicity. PBMCs from piperacillin-hypersensitive patients showed concentration-dependent, drug-specific proliferative responses associated with the release of cytokines and granzyme B. Modifications at lysine residues 190, 432, and 541 constituted the major epitopes for T cells. Finally, a synthetic piperacillin–albumin conjugate stimulated the proliferation of PBMCs and CD4+ clones from hypersensitive patients. This study, chemically identifying functional Ags formed in hapten-modified endogenous proteins upon drug exposure, may aid in the understanding of drug hypersensitivity.
Sordid Psoriasis Secretions
IL-17, a cytokine produced by T cells, plays a critical role in the development of psoriasis. Lin et al. (p. 490) investigated whether other cell types, particularly those involved in innate immunity, contribute to IL-17 production in this disease. Surprisingly, the majority of IL-17+ cells in psoriatic lesions and in normal skin from patients or from healthy controls did not express the T cell marker CD3. In contrast, mast cells (MCs) were enriched in skin lesions, compared with control skin, and, importantly, they were the main cell type containing IL-17 in the skin of psoriasis patients and healthy controls. Essentially all MCs in lesions were positive for the cytokine. IL-17+ neutrophils were also enriched in psoriatic lesions. In addition, the authors established that IL-17 was frequently associated with neutrophil extracellular trap (ET) formation. These traps are extracellular structures composed of granule proteins and chromatin that neutrophils and MCs generate in response to infection, as a means to kill bacteria. However, only few MC ETs were positive for IL-17, possibly because the cytokine might be released at a level below the assay threshold. Additional experiments demonstrated that IL-13 and IL-1β stimulated degranulation and creation of MC ETs. This study identifies MCs and neutrophils as important contributors to the pathogenesis of psoriasis.
Safer Salmonella Vaccines
Recombinant attenuated Salmonella has been considered as a potential Ag delivery system for vaccinations. However, its use has been hindered by the residual toxicity of bacterial components such as lipid A. In their search to produce less toxic Salmonella strains, Kong et al. (p. 412) tested a new approach to generating dephosphorylated lipid A, as two phosphate groups of lipid A are required for TLR4 activation by LPS. The authors successfully inserted the Francisella tularensis lpxE gene into the Salmonella genome. lpxE encodes a phosphatase that selectively removes the 1-phosphate group of lipid A. The resultant lpxE-expressing Salmonella strains X9732 and X9709 had significantly reduced virulence, as measured by the survival of infected mice. All the mice that received mutant strains survived subsequent challenge with the wild-type strain. In addition, lower levels of proinflammatory cytokines were observed after infection with an lpxE-expressing mutant strain versus the wild-type strain. Mutant strains were able to deliver the heterologous Ag pneumococcal surface protein A (PspA), and mice injected with an lpxE/PspA strain had increased survival after S. pneumoniae challenge compared with vector-immunized mice. These findings represent a further step in the development of safe Salmonella-based vaccines.
CD101: Basic Autoimmunity
Two articles in this issue focus on the involvement of the Cd101 gene in autoimmunity. First, Rainbow et al. (p. 325) performed haplotype analysis using newly developed congenic strains to explore whether Cd101 was the gene responsible for the diabetes susceptibility conferred by Idd10, a mouse genomic region including seven genes. Experiments with NOD, NOD.B6 Idd10, NOD.A/J Idd10, and NOD.CAST Idd10 demonstrated a genotype-dependent association with susceptibility or resistance to type 1 diabetes (T1D). The NOD.CAST Idd10 haplotype provided a NOD-type T1D susceptibility. In contrast, NOD.B6 Idd10 and NOD.A/J Idd10 haplotypes, which are identical at Cd101 but not at other genes within Idd10, were protective. The authors evaluated CD101 expression in the congenic mice. Expression levels were found to be genotype dependent on several cell subsets, with high CD101 levels on Gr1+ and Foxp3+ cells from the strains with protective haplotypes. Moreover, the diabetes-resistant mice had increased numbers of Gr1+ cells, whereas CD101-null B6 had few Gr1+ cells relative to wild-type mice. Taken together, these findings provide evidence that Cd101 is the gene within the Idd10 region that influences T1D susceptibility.
In the second article, Mohammed et al. (p. 337) examined the involvement of a gene protective for T1D, such as Cd101, in other autoimmune diseases. The authors used a model of autoimmune primary biliary cirrhosis (PBC) induced by infection with Novosphingobium aromaticivorans, and evaluated the development of PBC in CD101-null B6 mice, NOD.A/J Idd10 and NOD.B6 Idd10 mice (T1D-protective haplotypes), and NOD.CAST Idd10 mice (T1D-susceptible haplotype). Interestingly, the NOD.A/J Idd10 and NOD.B6 Idd10 mice developed severe liver disease upon infection, whereas disease was mild in the NOD.CAST Idd10 mice. In addition, the Cd101-null B6 mice exhibited severe PBC, compared with wild-type mice. These results suggest that allelic variations within Cd101 modulate the severity of infection-induced PBC and indicate that reduced CD101 expression correlates with increased liver pathology. Analysis of cellular populations in the liver of the PBC-susceptible NOD.B6 Idd10 mice showed that N. aromaticivorans infection caused reduced expression of CD101 on dendritic cells, macrophages, and granulocytes, with consequent increased expression of MHC class II on dendritic cells. This event, in turn, triggered enhancement of the activation state of T cells and release of IFN-γ and IL-17. The resultant inflammatory environment, together with reduced accumulation of granulocytes, might cause prolonged persistence of the bacteria in the liver and, consequently, the increased liver disease observed in PBC-prone mice. Together, the two studies identify Cd101 as a gene associated with two autoimmune diseases and suggest that allelic variations alter the severity of the diseases in opposite directions.
Summaries written by Bernardetta Nardelli, Ph.D.