Cystatin C regulates major histocompatibility complex-II-peptide presentation and extracellular signal-regulated kinase-dependent polarizing cytokine production by bone marrow-derived dendritic cells.

Cystatin C is a ubiquitously expressed cysteine protease inhibitor that protects cells from either improper hydrolysis by endogenous proteases or pathogen growth/virulence by exogenous proteases. Although commonly used as a serum biomarker for evaluating renal function, cystatin C is associated with many immunological disorders under various pathophysiological conditions. How cystatin C affects immune cells, especially dendritic cells (DCs), however, is far from clear. In this study, we found that pharmacological treatment with or genetic overexpression of cystatin C in bone marrow-derived DCs (BMDCs) reduced their capacity to stimulate CD4+ T-cell proliferation, despite increased antigen uptake. This reduced capacity corresponded with reduced major histocompatibility complex-II presentation owing to diminished levels of the chaperon H2-DM in BMDCs. Instead of promoting proliferation, cystatin C promoted skewing of T cells toward proinflammatory T-helper (Th)1/Th17 differentiation. This was mediated by augmented extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase phosphorylation in BMDCs, leading to secretion of polarizing cytokines, which in turn led to the Th deviation. Collectively, our study explained the cellular and molecular basis of how this protease inhibitor can regulate immune responses, namely by affecting BMDCs and their cytokine pathway. Our results might open up an avenue for the development of therapeutic agents for the treatment of cystatin C-related immunological diseases.

Inflammatory compound lipopolysaccharide promotes the survival of GM-CSF cultured dendritic cell via PI3 kinase-dependent upregulation of Bcl-x.

As professional antigen-presenting cells, dendritic cells (DCs) initiate and regulate immune responses against inflammation. The invasion of pathogens into the body, however, can in turn cause the change of DCs in both activity and viability, which ultimately affect immune homeostasis. The exact mechanisms that the bacteria utilize to alter the lifespan of DCs, however, are far from clear. In this study, we found that the bacterial wall compound lipopolysaccharide (LPS) can promote the survival of GM-CSF-differentiated DCs (GM-DCs). At molecular levels, we demonstrated that GM-DCs had distinct pattern of mRNA expression for anti-apoptotic BCL-2 family members, of which, Bcl-x increased significantly following LPS stimulation. Interestingly, specific inhibition of BCL-XL protein alone was sufficient to remove the anti-apoptotic effects of LPS on BM-DCs. Further study of the signaling mechanisms revealed that although LPS can activate both Erk MAP kinase and PI3 kinase pathways, only blocking of PI3K abolished both Bcl-x upregulation and the enhanced survival phenotype, suggesting that the PI3K signaling mediated the upregulation of Bcl-x for the LPS-induced pro-survival in GM-DCs. Collectively, this study unveils a molecular mechanism that DCs adapt to maintain innate immunity against the invasion of pathogens.

Bone marrow-derived inflammatory and steady state DCs are different in both functions and survival.

Dendritic cells (DCs) contain heterogeneous populations, with classical DCs developed at steady state and monocyte-derived DCs mobilized under inflammatory conditions, although their total numbers in vivo are scares. To obtain enough quantity for immunological study or clinical application, we have previously established that bone marrow-derived DCs in the presence of Flt-3L (FL-DCs) or GM-CSF (GM-DCs) in vitro are equivalent to the steady state DCs and inflammatory DCs in vivo respectively. What difference, however, exists between these two most commonly used culture systems in DC functions and survival, and how does it correlate to the division of works by their corresponding counterparts in vivo remain ill-defined. In this study, we found that GM-DCs of inflammatory nature were more phagocytic, potent at inducing Th2 and Th17 differentiation, and had longer survival rate, whereas FL-DCs of steady state characters were stronger T cell activator and better at directing Th1 differentiation. Mechanistically, NO production induced by the LPS-activated GM-DCs could partly explain for their failure to improve T cell proliferation, and the distinct T cell differentiation profiles and viability demonstrated by the two types of DCs were underpinned by their preferential secretion of T cell polarizing cytokines and expression of anti-apoptotic genes. Such disparate functionalities and survival potentials of steady state and inflammatory DCs in vitro fit in well with their respective roles in vivo in particular immunological settings and have serious implications in translational applications.

Involvement of cystatin C in immunity and apoptosis.

As an abundantly expressed cysteine protease inhibitor widely distributed in the organisms, cystatin C is involved in various physiological processes. Due to its relatively small molecular weight and easy detection, cystatin C is commonly used as a measure for glomerular filtration rate. In pathological conditions, however, growing evidences suggest that cystatin C is associated with various immune responses against either exogenous or endogenous antigens, which ultimately result in inflammatory autoimmune diseases or tumor development if not properly controlled. Thus the fluctuation of cystatin C levels might have more clinical implications than a reflection of kidney functions. Here, we summarize the latest development of studies on the pathophysiological functions of cystatin C, with focus on its immune regulatory roles at both cellular and molecular levels including antigen presentation, secretion of cytokines, synthesis of nitric oxide, as well as apoptosis. Finally, we discuss the clinical implications and therapeutic potentials of what this predominantly expressed protease inhibitor can bring to us.

CD19, from bench to bedside.

As a 95-kDa member of the immunoglobulin super-family expressed exclusively on B lymphocytes, CD19 is a critical co-receptor for B cell antigen receptor (BCR) signal transduction. Co-ligation of CD19 with the BCR synergistically enhances calcium release, mitogen-activated protein kinase activity and cell proliferation. However, CD19 deficient animals also display hyper-responsiveness under certain circumstances, indicating potential negative regulatory functions in BCR signaling. Thus CD19, like many other signaling molecules, is a double-edged sword and its abnormal expression can result in B cell related diseases. Here in this review, we summarize the latest development on the major functions of CD19 as both positive and negative regulator of BCR signaling in different situations and highlight the correlation and mechanisms of disturbed CD19 expression with autoimmune diseases and B cell lymphomas. Hopefully, the knowledge derived could shed an interesting light on the mechanistic insights of this important B cell surface molecule in both physiological and pathological conditions.