Chiann-Chyi Chen

Inflammatory Monocytes Orchestrate Innate Antifungal Immunity in the Lung

Aspergillus fumigatus is an environmental fungus that causes invasive aspergillosis (IA) in immunocompromised patients. Although -CC-chemokine receptor-2 (CCR2) and Ly6C-expressing inflammatory monocytes (CCR2+Mo) and their derivatives initiate adaptive pulmonary immune responses, their role in coordinating innate immune responses in the lung remain poorly defined. Using conditional and antibody-mediated cell ablation strategies, we found that CCR2+Mo and monocyte-derived dendritic cells (Mo-DCs) are essential for innate defense against inhaled conidia. By harnessing fluorescent Aspergillus reporter (FLARE) conidia that report fungal cell association and viability in vivo, we identify two mechanisms by which CCR2+Mo and Mo-DCs exert innate antifungal activity. First, CCR2+Mo and Mo-DCs condition the lung inflammatory milieu to augment neutrophil conidiacidal activity. Second, conidial uptake by CCR2+Mo temporally coincided with their differentiation into Mo-DCs, a process that resulted in direct conidial killing. Our findings illustrate both indirect and direct functions for CCR2+Mo and their derivatives in innate antifungal immunity in the lung.

Defective ubiquitin-mediated degradation of antiapoptotic Bfl-1 predisposes to lymphoma

The antiapoptotic Bcl-2 family member Bfl-1 is up-regulated in many human tumors in which nuclear factor-kappaB (NF-kappaB) is implicated and contributes significantly to tumor cell survival and chemoresistance. We previously found that NF-kappaB induces transcription of bfl-1 and that the Bfl-1 protein is also regulated by ubiquitin-mediated proteasomal degradation. However, the role that dysregulation of Bfl-1 turnover plays in cancer is not known. Here we show that ubiquitination-resistant mutants of Bfl-1 display increased stability and greatly accelerated tumor formation in a mouse model of leukemia/lymphoma. We also show that tyrosine kinase Lck is up-regulated and activated in these tumors and leads to activation of the IkappaB kinase, Akt, and extracellular signal-regulated protein kinase signaling pathways, which are key mediators in cancer. Coexpression of Bfl-1 and constitutively active Lck promoted tumor formation, whereas Lck knockdown in tumor-derived cells suppressed leukemia/lymphomagenesis. These data demonstrate that ubiquitination is a critical tumor suppression mechanism regulating Bfl-1 function and suggest that mutations in bfl-1 or in the signaling pathways that control its ubiquitination may predispose one to cancer. Furthermore, because bfl-1 is up-regulated in many human hematopoietic tumors, this finding suggests that strategies to promote Bfl-1 ubiquitination may improve therapy.

In vivo post-transcriptional regulation of CD154 in mouse CD4+ T cells

Interactions between CD40 and its ligand CD154 are involved in the progression of both cell mediated and innate immunity. These interactions are brought about by the transient expression of CD154 on activated CD4+ T cells, which is regulated, in part, at the level of mRNA turnover. Here we have focused on analyzing the pattern of post‐transcriptional regulation in mouse CD4+ T cells in response to activation. Initial experiments identify a region of the murine CD154 mRNA that binds a polypyrimidine tract‐binding protein‐containing complex (mComplex I), which is activation‐dependent and binds to a single CU‐rich site within the 3′ uTR Subsequent findings demonstrate that in vivo polyclonal activation of T cells leads to a pattern of differential CD154 mRNA stability that is directly dependent on extent of activation. Furthermore, in vitro activation of antigen‐primed T cells shows that the CD154 mRNA half‐life increases relative to that of unprimed cells. Importantly, this is the first report demonstrating that the regulation of CD154 in vivo is connected to an activation‐induced program of mRNA decay and thus provides strong evidence for post‐transcriptional mechanisms having a physiological role in regulating CD154 expression during an ongoing immune response.

Cross-reactive antibodies induced by xenogeneic IgA can cause selective IgA deficiency

Selective immunoglobulin A deficiency (sIgAD) is the most common immunodeficiency in humans. Auto-reactive antibodies to human immunoglobulin A (IgA) are found in the serum of 20–40% of individuals with sIgAD. It is unknown whether these antibodies play a role in the pathogenesis of this immunodeficiency and although the prevailing thought is that they are secondary to the onset of sIgAD, there is very little, if any, support for this notion. Here, we propose that anti-IgA antibodies are in fact responsible for the removal of IgA from serum, and that the inducing antigen is most probably a xenogeneic IgA. This hypothesis is based on data obtained from an sIgAD patient in whom changes in dietary consumption of beef and/or bovine dairy products resulted in changes in anti-IgA levels in the serum. To test the hypothesis, the presence of anti-bovine IgA antibodies was tested by a highly specific enzyme-linked immunosorbent assay in serum samples from IgA-deficient and control individuals. All 13 sIgAD individuals with anti-IgA antibodies had a higher titer against bovine IgA than against human IgA. Of 23 control individuals, a surprisingly high proportion (65%) was also found to have IgG anti-bovine IgA antibodies. These results support the hypothesis that the anti-human IgA antibodies found in IgA-deficient individuals are originally produced against bovine IgA. These antibodies are found in many normal individuals, but only in cases where they cross react with endogenous human IgA, sIgAD may develop.

New strategies for immune-mediated anti-viral drug and vaccine development.

Substantial progress in the development of new anti-viral drugs has taken place in recent years. Most of these new drugs belong to three groups of compounds, nucleoside analogs, thymidine kinase-dependent nucleotide analogs and specific viral enzyme inhibitors. Although these drugs revolutionized the treatment of several viral diseases, the involvement of the immune system is crucial for complete recovery and prevention of re-infection. New advances in the understanding of immune regulation mechanisms, mainly the role of cytokines, led to the development of several new immunologically-based anti-viral drugs and treatments. The most studied group of immunomodulators is the cytokines, some of which were shown to act as potent stimulators of immune responses. Other, non-cytokine immune modulators have also been successfully employed in both humans and experimental animals as anti-viral drugs of which several are currently in clinical trials. Advances in genetic engineering and transgenic mouse technologies facilitated the production of humanized as well as authentic human anti-viral monoclonal antibodies. Some of these antibodies proved to be clinically efficacious and are commercially produced as anti-viral drugs. As is often the case in anti-viral treatments, a combination of conventional and an immune-mediated anti-viral drugs or a combination therapy involving immunomodulators, therapeutic vaccines, immune intervention and even gene therapy might prove most efficacious as a treatment for a particular virus. Most of the advances made in anti-viral treatments have also been applied to the development of new vaccines. Some of the classical attenuated viruses are being replaced by recombinant attenuated viruses. Recombinant viral vaccines containing genes encoding other viral antigens and/or cytokines are being tested as new vaccines. Several chimeric viral vaccines have proven efficacious in experimental animals and are now in different phases of clinical trials. This review will encompass the major new developments in this field, including some that have not yet been subjected to human trials.

Isolation of multilineage progenitors from mouse brain

Stem cells are unique cell populations with the ability to undergo self-renewal and differentiation. These cells have been identified in a wide range of tissues and possess varied differentiation potentials. Tissue-specific stem cells have typically been thought to have limited differentiation capabilities. We show here that fibroblast-like cells isolated from mouse brain possess cross-germ layer differentiation abilities. These cells were found to express typical mesenchymal stem cell markers (CD44, CD29, and CD105) and were able to be passaged more than 50 times. When treated under defined conditions, the brain-derived cells were able to generate many different cell types including adipocytes, osteocytes, astrocytes, neurons, and even hepatocyte-like cells. The hepatocyte-like cells not only expressed liver cell-specific markers, but also exhibited the capacity for glycogen storage and low-density lipoprotein uptake. These results demonstrate the existence of cells in the brain with three-germ-layer differentiation potential.