C-terminal citrullinated peptide alters antigen-specific APC:T cell interactions leading to breach of immune tolerance.

In rheumatoid arthritis, the emergence of anti-citrullinated autoimmunity is associated with HLA-antigen-T cell receptor complexes. The precise mechanisms underpinning this breach of tolerance are not well understood. Porphyromonas gingivalis expresses an enzyme capable of non-endogenous C-terminal citrullination with potential to generate citrullinated autoantigens. Here we document how C-terminal citrullination of ovalbumin peptide323-339 alters the interaction between antigen-presenting cells and OTII T cells to induce functional changes in responding T cells. These data reveal that C-terminal citrullination is sufficient to breach T cell peripheral tolerance in vivo and reveal the potential of C-terminal citrullination to lower the threshold for T cell activation. Finally, we demonstrate a role for the IL-2/STAT5/CD25 signalling axis in breach of tolerance. Together, our data identify a tractable mechanism and targetable pathways underpinning breach of tolerance in rheumatoid arthritis and provide new conceptual insight into the origins of anti-citrullinated autoimmunity.

Mast Cells Contribute to Porphyromonas gingivalis-induced Bone Loss.

Periodontitis is a chronic inflammatory and bone-destructive disease. Development of periodontitis is associated with dysbiosis of the microbial community, which may be caused by periodontal bacteria, such as Porphyromonas gingivalis Mast cells are sentinels at mucosal surfaces and are a potent source of inflammatory mediators, including tumor necrosis factors (TNF), although their role in the pathogenesis of periodontitis remains to be elucidated. This study sought to determine the contribution of mast cells to local bone destruction following oral infection with P. gingivalis Mast cell-deficient mice (Kit(W-sh/W-sh)) were protected from P. gingivalis-induced alveolar bone loss, with a reduction in anti-P. gingivalis serum antibody titers compared with wild-type infected controls. Furthermore, mast cell-deficient mice had reduced expression of Tnf, Il6, and Il1b mRNA in gingival tissues compared with wild-type mice. Mast cell-engrafted Kit(W-sh/W-sh) mice infected with P. gingivalis demonstrated alveolar bone loss and serum anti-P. gingivalis antibody titers equivalent to wild-type infected mice. The expression of Tnf mRNA in gingival tissues of Kit(W-sh/W-sh) mice was elevated following the engraftment of mast cells, indicating that mast cells contributed to the Tnf transcript in gingival tissues. In vitro, mast cells degranulated and released significant TNF in response to oral bacteria, and neutralizing TNF in vivo abrogated alveolar bone loss following P. gingivalis infection. These data indicate that mast cells and TNF contribute to the immunopathogenesis of periodontitis and may offer therapeutic targets.

Lymphocytes protect cortical neurons against excitotoxicity mediated by kainic acid, an in vitro model for neurodegeneration.

BACKGROUND: Neurodegenerative disease is a progressive loss of neurons from the central nervous system (CNS). Various conditions have been implicated for such conditions including ageing, inflammation, stress and genetic predisposition. Recently, studies have linked neurodegeneration with inflammation. Some studies have suggested the harmful effect of immune response while others have argued its neuroprotective role in neurodegeneration of the CNS. However, the precise role of inflammation and immune cells in such condition is still not clear. OBJECTIVE: To investigate the role of lymphocytes in neurodegeneration of the CNS and determine the underlying mechanism. METHOD: We have used 4-7 days old mouse pups (C57Bl6) to prepare organotypic slice cultures which were cultured for 13-15 days prior to experiment. To induced cell death kainic acid was used and considered as an in vitro model for neurodegeneration. Lymphocytes were obtained from peripheral lymph nodes of 5-10 weeks old adult mouse which were used in the current study. Propidium iodide was used as a fluorescent dye to determine cell death in brain slice cultures. RESULT: Lymphocytes do not induce cell death in slice cultures in the absence of any toxic insult whereas, after applying toxic insult to the slice cultures using kainic acid, lymphocytes show neuroprotection against such insult. Similarly, purified nonactivated and purified activated T cells along with T cells depleted lymphocyte preparation also exhibit neuroprotection against kainic acid-induced cell death. We further, have demonstrated that the observed neuroprotection is contact-independent and soluble mediators released from lymphocytes are responsible for the observed neuroprotection. Moreover, our study has revealed that soluble mediators exhibiting neuroprotection act via astrocytes. CONCLUSION: Lymphocyte preparations are neuroprotective and the observed neuroprotection is contact-independent. Soluble mediators released from lymphocytes are responsible for the observed neuroprotection.

Is central nervous system an immune-privileged site?

The central nervous system (CNS) was once considered to be an immune-privileged area. However, increasing evidence shows that the central nervous system is not an immune-privileged but is an active surveillance site. There is a bi-directional communication between the central nervous system and immune system. Normally, immune cells migrate into the central nervous system microenvironment through choroid plexus and interact with the central nervous system resident cells through either through neuromediators or immunomediators. This finding has led to a significant interest in neuroimmunological interactions and investigation onto the role of the immune system in the pathology of various neurological disorders and examine whether it can be targeted to produce novel therapeutic strategies.

Advances in imaging of new targets for pharmacological intervention in stroke: real-time tracking of T-cells in the ischaemic brain.

BACKGROUND AND PURPOSE: T-cells may play a role in the evolution of ischaemic damage and repair, but the ability to image these cells in the living brain after a stroke has been limited. We aim to extend the technique of real-time in situ brain imaging of T-cells, previously shown in models of immunological diseases, to models of experimental stroke. EXPERIMENTAL APPROACH: Male C57BL6 mice (6-8 weeks) (n= 3) received a total of 2-5 x 10(6) carboxyfluorescein diacetate succinimidyl ester (CFSE)-labelled lymphocytes from donor C57BL6 mice via i.v. injection by adoptive transfer. Twenty-four hours later, recipient mice underwent permanent left distal middle cerebral artery occlusion (MCAO) by electrocoagulation or by sham surgery under isoflurane anaesthesia. Female hCD2-green fluorescent protein (GFP) transgenic mice that exhibit GFP-labelled T-cells underwent MCAO. At 24 or 48 h post-MCAO, a sagittal brain slice (1500 microm thick) containing cortical branches of the occluded middle cerebral artery (MCA) was dissected and used for multiphoton laser scanning microscopy (MPLSM). KEY RESULTS: Our results provide direct observations for the first time of dynamic T-cell behaviour in living brain tissue in real time and herein proved the feasibility of MPLSM for ex vivo live imaging of immune response after experimental stroke. CONCLUSIONS AND IMPLICATIONS: It is hoped that these advances in the imaging of immune cells will provide information that can be harnessed to a therapeutic advantage.

Imaging T-cell movement in the brain during experimental cerebral malaria.

T-cells are known to play a role in the pathology associated with experimental cerebral malaria, although it has not previously been possible to examine their behaviour in brain. Using multiphoton laser scanning microscopy, we have examined the migration and movement of these cells in brain tissue. We believe that this approach will help define host-parasite interactions and examine how intervening in these relationships affects the development of cerebral pathology.

What can transgenic parasites tell us about the development of Plasmodium-specific immune responses?

Malaria infects 500 million people and kills an estimated 2.7 million annually, representing one of the most significant diseases in the world. However, efforts to develop effective vaccines have met with limited success. One reason is our lack of basic knowledge of how and where the immune system responds to parasite antigens. This is important as the early events during induction of an immune response influence the acquisition of effector function and development of memory responses. Our knowledge of the interactions of Plasmodia with the host immune system has largely been derived through in vitro study. This is a significant issue as the component parts of the immune system do not work in isolation and their interactions occur in distinct and specialized micro- and macro-anatomical locations that can only be assessed in the physiological context, in vivo. In this context, the availability of transgenic malaria parasites over the last 10 years has greatly enhanced our ability to understand and evaluate factors involved in host-parasite interactions in vivo. In this article, we review the current status of this area and speculate on what parasite transgenesis approaches will tell us about the development of Plasmodium-specific immune responses in the future.

Lymphocyte tracking and interactions in secondary lymphoid organs.

The induction of an adaptive immune response is an essential step in the generation of long-lasting, protective immunity to pathogens. Many studies over the last few decades have identified the cell populations involved in the generation of antigen-specific immunity and elucidated the role of many important molecules. However, because of the low precursor frequency of antigen-specific cells, the immune system must be highly dynamic, surveying most sites of the body. Recent studies have, therefore, begun to examine how the cells of the immune system interact in vivo during the induction of an immune response, identifying new and important roles for certain molecules and revealing how previously unrecognised alterations in cell-cell interactions can have significant implications for the resulting immune response. Here we review some of these recent studies that provide a valuable insight into the mechanisms involved in the induction of immunity.