Use of proteomics to define targets of T-cell immunity

The mammalian immune system has evolved to display peptides derived from microbial antigens to immune effector cells. Liberated from the intact antigens through distinct proteolytic mechanisms, these peptides are subsequently transported to the cell surface while bound to chaperone-like receptors known as major histocompatibility complex molecules. These complexes are then scrutinized by T-cells that express receptors with specificity for specific major histocompatibility complex–peptide complexes. In normal uninfected cells, this process of antigen processing and presentation occurs continuously, with the resultant array of self-antigen-derived peptides displayed on the surface of these cells. Changes in this cellular peptide array alert the immune system to changes in the intracellular environment that may be associated with infection, oncogenesis or other abnormal cellular processes, resulting in a cascade of events that result in the elimination of the abnormal cell. Since peptides play such an essential role in informing the immune system of infection with viral or microbial pathogens and the transformation of cells in malignancy, the tools of proteomics, in particular mass spectrometry, are ideally suited to study these immune responses at a molecular level. Recent advances in studies of immune responses that have utilized mass spectrometry and associated technologies are reviewed. The authors gaze into the future and look at current challenges and where proteomics will impact in immunology over the next 5 years.     

Use of proteomics to define targets of T-cell immunity

The mammalian immune system has evolved to display peptides derived from microbial antigens to immune effector cells. Liberated from the intact antigens through distinct proteolytic mechanisms, these peptides are subsequently transported to the cell surface while bound to chaperone-like receptors known as major histocompatibility complex molecules. These complexes are then scrutinized by T-cells that express receptors with specificity for specific major histocompatibility complex-peptide complexes. In normal uninfected cells, this process of antigen processing and presentation occurs continuously, with the resultant array of self-antigen-derived peptides displayed on the surface of these cells. Changes in this cellular peptide array alert the immune system to changes in the intracellular environment that may be associated with infection, oncogenesis or other abnormal cellular processes, resulting in a cascade of events that result in the elimination of the abnormal cell. Since peptides play such an essential role in informing the immune system of infection with viral or microbial pathogens and the transformation of cells in malignancy, the tools of proteomics, in particular mass spectrometry, are ideally suited to study these immune responses at a molecular level. Recent advances in studies of immune responses that have utilized mass spectrometry and associated technologies are reviewed. The authors gaze into the future and look at current challenges and where proteomics will impact in immunology over the next 5 years.     

SIRT1 longevity factor suppresses NF‐κB ‐driven immune responses: regulation of aging via NF‐κB acetylation?

The aging process involves changes in immune regulation, i.e. adaptive immunity declines whereas innate immunity becomes activated. NF-kappaB signaling is the master regulator of the both immune systems. Two recent articles highlight the role of the NF-kappaB system in aging and immune responses. Adler et al showed that the NF-kappaB binding domain is the genetic regulatory motif which is most strongly associated with the aging process. Kwon et al studying HIV-1 infection and subsequent immune deficiency process demonstrated that HIV-1 Tat protein binds to SIRT1 protein, a well-known longevity factor, and inhibits the SIRT1-mediated deacetylation of the p65 component of the NF-kappaB complex. As a consequence, the transactivation efficiency of the NF-kappaB factor was greatly potentiated, leading to the activation of immune system and later to the decline of adaptive immunity. These observations support the scenario where immune responses and aging process can be enforced by the potentiation of NF-kappaB transactivation efficiency. Longevity factors, such as SIRT1 and its activators, might regulate the efficiency of the NF-kappaB signaling, the major outcome of which is inflamm-aging via proinflammatory responses.     

NF-kappa B controls cell fate specification, survival, and molecular differentiation of immunoregulatory natural T lymphocytes

Ontogenetic, homeostatic, and functional deficiencies within immunoregulatory natural T (iNKT) lymphocytes underlie various inflammatory immune disorders including autoimmunity. Signaling events that control cell fate specification and molecular differentiation of iNKT cells are only partly understood. Here we demonstrate that these processes within iNKT cells require classical NF-kappaB signaling. Inhibition of NF-kappaB signaling blocks iNKT cell ontogeny at an immature stage and reveals an apparent, novel precursor in which negative selection occurs. Most importantly, this block occurs due to a lack of survival signals, as Bcl-x(L) overexpression rescues iNKT cell ontogeny. Maturation of immature iNKT cell precursors induces Bcl-2 expression, which is defective in the absence of NF-kappaB signaling. Bcl-x(L) overexpression also rescues this maturation-induced Bcl-2 expression. Thus, antiapoptotic signals relayed by NF-kappaB critically control cell fate specification and molecular differentiation of iNKT cells and, hence, reveal a novel role for such signals within the immune system.     

Constitutive production of NF-kappaB2 p52 is not tumorigenic but predisposes mice to inflammatory autoimmune disease by repressing Bim expression

Normal development of the immune system requires regulated processing of NF-kappaB2 p100 to p52, which activates NF-kappaB2 signaling. Constitutive production of p52 has been suggested as a major mechanism underlying lymphomagenesis induced by NF-kappaB2 mutations, which occur recurrently in a variety of human lymphoid malignancies. To test the hypothesis, we generated transgenic mice with targeted expression of p52 in lymphocytes. In contrast to their counterparts expressing the tumor-derived NF-kappaB2 mutant p80HT, which develop predominantly B cell tumors, p52 transgenic mice are not prone to lymphomagenesis. However, they are predisposed to inflammatory autoimmune disease characterized by multiorgan infiltration of activated lymphocytes, high levels of autoantibodies in the serum, and immune complex glomerulonephritis. p52, but not p80HT, represses Bim expression, leading to defects in apoptotic processes critical for elimination of autoreactive lymphocytes and control of immune response. These findings reveal distinct signaling pathways for actions of NF-kappaB2 mutants and p52 and suggest a causal role for sustained NF-kappaB2 activation in the pathogenesis of autoimmunity.     

Acrolein with an alpha, beta-unsaturated carbonyl group inhibits LPS-induced homodimerization of toll-like receptor 4

Acrolein is a highly electrophilic alpha,beta-unsaturated aldehyde present in a number of environmental sources, especially cigarette smoke. It reacts strongly with the thiol groups of cysteine residues by Michael addition and has been reported to inhibit nuclear factor-kappaB (NF-kappaB) activation by lipopolysaccharide (LPS). The mechanism by which it inhibits NF-kappaB is not clear. Toll-like receptors (TLRs) play a key role in sensing microbial components and inducing innate immune responses, and LPS-induced dimerization of TLR4 is required for activation of downstream signaling pathways. Thus, dimerization of TLR4 may be one of the first events involved in activating TLR4-mediated signaling pathways. Stimulation of TLR4 by LPS activates both myeloid differential factor 88 (MyD88)- and TIR domain-containing adapter inducing IFNbeta(TRIF)-dependent signaling pathways leading to activation of NF-kappaB and IFN-regulatory factor 3 (IRF3). Acrolein inhibited NF-kappaB and IRF3 activation by LPS, but it did not inhibit NF-kappaB or IRF3 activation by MyD88, inhibitor kappaB kinase (IKK)beta, TRIF, or TNF-receptor-associated factor family member-associated NF-kappaB activator (TANK)-binding kinase 1 (TBK1). Acrolein inhibited LPS-induced dimerization of TLR4, which resulted in the down-regulation of NF-kappaB and IRF3 activation. These results suggest that activation of TLRs and subsequent immune/inflammatory responses induced by endogenous molecules or chronic infection can be modulated by certain chemicals with a structural motif that enables Michael addition.     

Viral appropriation of apoptotic and NF-kappaB signaling pathways

Viruses utilize a variety of strategies to evade the host immune response and replicate in the cells they infect. The comparatively large genomes of the Orthopoxviruses and gammaherpesviruses encode several immunomodulatory proteins that are homologous to component of the innate immune system of host cells, which are reviewed here. However, the viral mechanisms used to survive host responses are quite distinct between these two virus families. Poxviruses undergo continuous lytic replication in the host cytoplasm while expressing many genes that inhibit innate immune responses. In contrast, herpesviruses persist in a latent state during much of their lifecycle while expressing only a limited number of relatively non-immunogenic viral proteins, thereby avoiding the adaptive immune response. Poxviruses suppress, whereas latent gammaherpesviruses activate, signaling by NF-kappaB, yet both viruses target similar host signaling pathways to suppress the apoptotic response. Here, modulation of apoptotic and NF-kappaB signal transduction pathways are examined as examples of common pathways appropriated in contrasting ways by herpesviruses and poxviruses.