We like inflammation Prof. Dr. Albert Duschl
Clinical definition The classical signs of Inflammation are: 1. Reddening (rubor) 2. Heat (calor) 3. Swelling (tumor) 4. Pain (dolor) 5. Impaired function (functio laesa) At least # 1-4 are good for you. We can even argue about # 5 being useful. We like inflammation! Let s say only nice things about it today. Paul: Fundamental Immunology
Local / Systemic Inflammation has local and systemic aspects. The five classic signs of inflammation are observed locally. It is a key task of immunity to keep pathogens localized. Systemic responses are fever and acute phase. Other reactions may also be useful, like sleepiness. Inflammation is triggered and maintained by the body. The inflammation process is the mechanisms how the body resolves threats by pathogens and other factors. It starts with innate immune activation, may proceed to type 1 adaptive immune response, and closes with healing. Wood: Understanding Immunology
Acute phase IL-1, TNF-a, but particularly IL-6 induce systemically the acute phase, an alarm reaction of the body against serious threats. Hepatocytes produce numerous serum proteins in 1.5-1000 fold increased amounts. These acute phase proteins are all involved in defending the body. Janeway: Immunobiology Among the proteins that are most strongly induced are Serum Amyloid A (inhibits fever and platelet activation: negative feedback) and C- reactive Protein (binds phosphorylcholine of bacteria and damaged cells, leads to opsonisation. Other proteins are involved in coagulation (fibrinogen, prothrombin), vasodilation and vasopermeability (prekallikrein), protease inhibition (a1-antitrypsin) and opsonisation (like the C-reactive protein. Of course, all the complement factors are acute phase proteins as well.
Complement Interestingly, the classical pathway of complement activation is the most novel one. While B-like cells are found in more distant relatives, proper antibodies appear only in jawed vertebrates (teleost fish). The recognition of bacterial lectins and other bacterial compounds is certainly older. The observation is in agreement with the opinion that humans are basically modified fish. (For a further elaboration on this issue see Neil Shubin s book Your inner fish ). Science, 31. Aug. 1012, Vol 337, p. 1035
Healthy tissue (as an example: Skin) Normal microflora. Normal levels/values for antimicrobial peptides, temperature, ph and so forth. DCs are present. Epidermal T-cells are present. No leukocyte infiltration. HOMEOSTASIS intact. The barrier function is intact. That is a key aspect for all body surfaces. Miller and Cho: Nat. Rev. Immunol. 11:505-18 (2011)
Compromised tissue Pathological microflora, invasion of tissue. Pro-forms of inflammatory cytokines are cleaved. For IL-1a Calpain is important, for IL-1b Caspase 1 (both are cysteine proteases). Increased production of antimicrobial peptides, lower ph, higher temperature. Leukocyte invasion. DCs and T-cell are activating adaptive immunity. HOMEOSTASIS lost. Miller and Cho: Nat. Rev. Immunol. 11:505-18 (2011)
Antimicrobial peptides Three are several familes of antimicrobial peptides (AMP). They are an evolutionary ancient protection against bacteria, viruses and fungi. AMP are found even in plants. An example are the defensins. They are small proteins (18-45 aa) which are strongly cationic and rich in cysteines. They penetrate into membranes and form pores. Other AMP are anionic peptides, or linear a-helical cationic peptides. They all are directly antibiotic. Since the AMPs are constantly produced they are in balance with the normal bacterial microflora. The gut microflora, for example, is adapted to live with the normal levels of AMPs that are present in their environment. Monomeres und dimeres Beta-Defensin 2 Wikimedia Commons
Inflammasome Three are several inflammasome proteins, which can activate the inflammation cascade. The NLR family and the PYHIN family have different domains. LRR and HIN200 are involved in ligand binding, NBD (NACHT, NOD domain) in homodimerization. PYD and CARD domains mediate heterodimerization. ASC is an adaptor molecule used in several inflammasome complexes. There are numerous ways to compose a functional inflammasome and not all receptors are shown here. If you like the Lego block feeling, I recommend the FIIND domain (domain with function to find). Strowig et al., Nature 481: 278-286 (2012)
Activation The paradigmatic function of the various inflammasome complexes is to induce the dimerization of caspase 1, which activates this protease. Active caspase 1 cleaves pro-il-ß (and also IL-18, another member of the IL-1 cytokine family with similar functions). Many signals are able to induce inflammasome activation, including ROS, lysosome rupture, DNA (do you have DNA in the cytoplasm?), and bacterial compounds like MDP and flagellin. Strowig et al., Nature 481: 278-286 (2012)
IL-1ß IL-1ß is a cytokine, but it is produced without signal sequence. Thus, it is not secreted but stored as a pro-form in the cytoplasm. This allows a very fast response. Cleavage induces secretion, via mechanisms that are not fully understood. Nature Review Immunology yearly calender, February 2012 OK, the contrast is weak, but I bet you don t have that calender.
Pyroptosis Abortive inflammation can result in pyroptosis. This form of cell death is (at least partially) programmed like apoptosis but releases DAMPs like necrosis. It is distinctive from both. In HIV, infection many T-cells die at the beginning of infection, while the rate of HIV + T-cells is still low. These cells abort infection, but incomplete transcripts from the reverse transcriptase are recognized as danger signals, leading to pyroptosis: T-cell depletion and inflammation ensue. Nature 505:492 (2014)
Neutrophils - classical Neutrophils are highly efficient in the phagocytosis of opsonized particles (bacteria, viruses etc.). They have several ways to kill bacteria: ROS production (oxidative burst) can directly attack pathogens. AMPs, including defensins, are particularly well suited to attack damaged membranes. Proteases (Cathepsin G, neutrophile collagenase, elastase etc.) and acidic hydrolases attack bacterial compounds. Binding proteins deprive bacteria of nutrients: Lactoferrin Fe and Cu, Transcobalamin Vitamin B12, Calprotectin Mn 2+, Zn 2+ etc. Miller and Cho: Nat. Rev. Immunol. 11:505-18 (2011)
Neutrophils as regulators Is was recognized only quite recently that neutrophils are not only effectors, but regulators as well. They produce substantial amounts of cytokines and chemokines. It is not coming as a big surprise that they produce proinflammatory factors, but interestingly, the strongly immunosuppressive cytokines TGF-ß and IL-10 are secreted as well. Neutrophils produce even angiogenic and fibrogenic factors, which implies that they are involved in wound healing. Mantovani et al. Nat. Rev. Immunol. 11: 519-31 (2011)
NET Neutrophil extracellular traps (NET) are produced when neutrophils degrade their nuclear membranes during apoptosis. Chromatin decondenses and is expulsed from the cell. Mitochondrial DNA and different kinds of granula can also be involved. NET localize bacteria and kill them via antibacterial factors contained in the NET. DNA is a sticky substance (remember shearing it!) from which bacteria cannot easily escape Remind me to tell you later what NET can do with carbon nanotubes. Mantovani et al. Nat. Rev. Immunol. 11: 519-31 (2011)
Neutrophile: Born to die Neutrophiles are like all leukocytes derived from stem cells in bone marrow. They do not proliferate, have a lobed nucleus and live normally only 10-12 h. Activated neutrophils can live up to 72 h in vitro. Their normal fate is apoptosis (or NETosis) which is necessary since they can eat and kill bacteria, but are not competent for digestion. Apoptotic bodies derived from neutrophils are eaten by macrophages. Inducing up-regulation of neutrophil differentiation by drugs like GM-CSF was a major clinical breakthrough. Neutrophile granulocyte, Wright staining, diameter 12 µm Wikimedia Commons
Macrophage: Born to eat Macrophages (MΦ) are highly phagocytic, but are long-lived and able to proliferate. They are professional antigen presenting cells (APCs the other two pros are B-cells and, as major APCs, of course DCs), Macrophages are powerful producers of cytokines and thus also have regulatory functions. Their precursors are monocytes, which are derived from stem cells in bone marrow. If you get lost on blood cell types, check out the free applet by STEMCELL Technologies on their frequencies and functions. Makrophagen, Trypan Blau Färbung Wikipedia
M1/M2 Different subsets of macrophages clearly associate with T H 1 or T H 2 responses (and thus with type 1 or type 2 adaptive immunity). They were described accordingly as M1 and M2 subtypes. If you look at the marker genes it is easy to see who does what. Murray and Wynn, Nat Rev Immunol 11:723-737 (2011)
Defense / Healing M2 are not only associated with T H 2 responses, but also with wound healing. Body barriers are reconstructed and the inner tissues regenerate, if possible without permanent scar formation. It is worth pondering that TGF-ß, a cytokine much involved in wound healing, is also a powerful tumor suppressor. Murray and Wynn, Nat Rev Immunol 11:723-737 (2011)
Inflammation is good The term inflammation is often used nearly synonymously with innate immunity. Type 1 adaptive immunity can be seen as a logical continuation of anti-pathogenic response. Adaptive immunity starts in a situation where an innate immune response is ongoing. It is thus shaped by the compromised environment and the actions already taken to counter a specific threat. Inflammation is your best bet to regain homeostasis after you have been colonized by pathogens. That is a valuable survival factor. Ring-a-ring of roses A pocketful of posies Attischo, Attischo, We all fall down. English ChildrEn s rhyme, 17th CEntury. Weekly death register of London for the week of 31rd August 1665. 8,297 dead, of which 7,165 died by bubonic plague. Reproduced from Samuel Pepys, Diaries, but I have not the foggiest who holds the of the London death register for the 17 th century.