Inflammation

Introduction

Inflammation is part of the complex biological reaction of the tissues of the body to harmful stimuli, such as bacteria, damaged cells or irritants, and is a defensive reaction involving immune cells, blood vessels and molecular mediators. 

Inflammation has the purpose of removing the initial cause of cell injury, clearing necrotic cells and damaged tissues from the initial insult and inflammatory process, and initiating tissue repair.

Inflammation is a generalized response, and thus, opposed to adaptive immunity, which is unique to each pathogen, it is regarded as a mechanism of innate immunity. Too little inflammation could cause the harmful stimulus (e.g. bacteria) to slowly kill tissue and threaten the organism’s survival.

There are two main types of inflammation:

1. Acute inflammation: It typically occurs for a short time (though sometimes severe). In two weeks or less, it generally resolves itself. Symptoms soon emerge of an injury or illness after acute inflammation is seen in the body.

2. Chronic inflammation: It is a slower form of inflammation and usually less severe. Usually, it lasts longer than 6 weeks. Even when there is no prominent disease, injury or illness, it can happen, and it doesn’t necessarily stop when the disease or injury is cured. Autoimmune conditions and even prolonged stress have been associated with chronic inflammation.

Inflammation symptoms

The five major signs that indicate the presence of inflammation are:

• heat
• pain
• redness
• swelling
• loss of function

Symptoms widely depend on the stage and condition that causes the inflammation in the body. Other symptoms that are observed in chronic inflammation include:

• body pain
• constant fatigue and insomnia
• depression, anxiety, and other mood disorders
• gastrointestinal issues, like constipation, diarrhea, and acid reflux
• weight gain
• frequent infections

Causes that lead to inflammation in the body

There are different factors which cause inflammation in the body. 

This include:

• Acute and chronic disorders 
• Some drugs 
• The body cannot quickly remove exposure to irritants or foreign materials. 

A chronic inflammatory response may also arise from repeated episodes of acute inflammation. 

In persons with autoimmune conditions, there are also certain forms of foods that can induce or exacerbate inflammation. 

These foods include:

• sugar
• refined carbohydrates
• alcohol
• processed meats
• trans fats

Treatment of Inflammation

There are a number of tests that can be carried out which show the presence of inflammation in the body. It can be as easy to combat inflammation as improving one’s diet.Inflammation is greatly subsided by eliminating sugar, trans fats, and processed foods. Some common anti-inflammatory foods are:

• berries and cherries
• fatty fish
• broccoli
• avocados
• green tea
• Tomatoes

Other remedies that can be practiced are:

• Consistently take required vitamins. 
• To decrease swelling and pain,  hot or cold treatment for physical wounds can be used.
• Exercise more often.
• Manage and lower the levels of stress. 
• Stop smoking. 
• Treat any preexisting conditions and control them.

Other treatment options:

NSAIDs and aspirin

In treating short-term pain and inflammation, non-steroidal anti-inflammatory drugs (NSAIDs) are typically the first line of protection. It is an over the counter drug.

NSAIDs that are popular include: 

• Aspirin
• ibuprofen (Advil, Motrin, Midol) 
• naproxen (Aleve)

Corticosteroids 

Corticosteroids are a form of steroid widely used to treat allergic reactions as well as swelling and inflammation. 

Typically, corticosteroids come as either a nasal spray or an oral pill. 

Article By- Ria Fazulbhoy (MSIWM031)

THE PROCESS OF THE INFLAMMATION

BY : K. Sai Manogna (MSIWM014)

Inflammation is a systemic reaction for several causes, such as tissue damage and infections. An acute inflammatory response typically has a fast onset and lasts for a short time. In general, acute inflammation is followed by a systemic reaction known as an acute-phase response, marked by a rapid shift in the concentrations of many plasma proteins. Persistent immune activation in certain diseases can lead to chronic inflammation, which often has pathological implications.

An essential role of neutrophils in inflammation:

1. The predominant cell type infiltrating the tissue is the neutrophil at the early stages of an inflammatory response.

2. Within the first six hours of an inflammatory response, neutrophil penetration into the tissue peaks, with development of neutrophils in the bone marrow growing to meet this need.

3. An average adult produces more than 10¹⁰ neutrophils per day, but during a time of acute inflammation, neutrophil production can increase by as much as tenfold.

4. The bone marrow is left by the neutrophils and circulates inside the blood.

5. Vascular endothelial cells increase their expression of E- and P-selectin in response to the mediators of acute inflammation.

6. Increased P-selectin expression is caused by thrombin and histamine; cytokines like IL-1 or TNF-induce increased E-selectin expression. The circulating neutrophils express mucins such as PSGL-1 or the tetrasaccharides Lewis^a sialyl and Lewis^x sialyl bind to E- and P-selectin.

7. This binding mediates the attachment or tethering of neutrophils to the vascular endothelium, enabling the cells to roll in the direction of blood flow.

8. Chemokines such as IL-8 or other chemoattractants function on the neutrophils during this time, causing an activating signal mediated by G-protein that leads to a conformational shift in the molecules of integrin adhesion, resulting in neutrophil adhesion and subsequent transendothelial migration.

9. When in tissues, activated neutrophils also express elevated levels of chemoattractant receptors and thus show chemotaxis, migrating up the chemoattractant gradient.

10. Several chemokines, complement split products (C3a, C5a, and C5b67), fibrinopeptides, prostaglandins, and leukotrienes are among the inflammatory mediators that are chemotactic to neutrophils.

11. Furthermore, microorganism-released compounds, such as formyl methionyl peptides, are also chemotactic to neutrophils.

12. Increased levels of Fc antibody receptors and complement receptors are expressed by activated neutrophils, allowing these cells to bind more efficiently to antibody- or complement-coated pathogens, thereby increasing phagocytosis.

13. The triggering signal also activates the metabolic pathways into a respiratory burst, creating intermediates of reactive oxygen and intermediates of reactive nitrogen.

14. In the killing of different pathogens, the release of some of these reactive intermediates and the release of mediators from neutrophil primary and secondary granules (proteases, phospholipases, elastases and collagenases) play a significant role.

15. The tissue damage that can result from an inflammatory reaction also leads to these substances. The aggregation, along with accumulated fluid and different proteins, of dead cells and microorganisms, makes up what is known as pus.

Inflammatory Responses:

A complex cascade of non-specific events, known as an inflammatory response, is caused by infection or tissue injury, which provides early protection by minimising tissue damage to the site of the infection or tissue injury. Both localised and systemic responses are involved in the acute inflammatory response.

LOCALISED INFLAMMATORY RESPONSE:

Redness, swelling, pain, heat, and loss of function are the hallmarks of a localised acute inflammatory response first identified almost 2000 years ago. There is an increase in vasodilation within minutes of tissue injury, resulting in an increase in the area’s blood volume and a decrease in blood flow. The increased volume of blood heats the tissue and causes it to turn red. Vascular permeability also increases, leading to fluid leakage, especially in postcapillary venules, from the blood vessels. This results in the fluid deposition in the tissue and, in some cases, leukocyte extravasation, which leads to the area’s swelling and redness. The kinin, clotting, and fibrinolytic processes are triggered when fluid exudes from the bloodstream. The direct effects of plasma enzyme mediators like bradykinin and fibrinopeptides, which induce vasodilation and increased vascular permeability, are responsible for many of the vascular changes that occur early in the local response. Some of these vascular changes are due to the indirect effects of histamine-released complement anaphylatoxins (C3a, C4a, and C5a) that induce local mast-cell degranulation.

1. Histamine is a potent inflammatory mediator, inducing vasodilation and contraction of smooth muscle.

2. Prostaglandins may also contribute to the acute inflammatory response associated with vasodilation and increased vascular permeability.

3. Neutrophils bind to the endothelial cells within a few hours of the initiation of these vascular changes and move from the blood into the tissue areas.

4. These phagocytose neutrophils invade pathogens and release mediators that lead to the inflammatory reaction.

5. The macrophage inflammatory proteins (MIP-1 and MIP-1), chemokines which attract macrophages to the inflammation site, are among the mediators. Around 5-6 hours after an inflammatory response starts, macrophages arrive.

6. These macrophages are activated cells that show increased phagocytosis and increased release of mediators and cytokines that contribute to the inflammatory response.

7. Three cytokines (IL-1, IL-6, and TNF-𝛼) that induce activated tissue macrophages secrete many of the localised and systemic changes, which observed in the acute inflammatory response.

8. All three cytokines function locally, causing coagulation and vascular permeability to increase.

9. Both TNF-𝛼 and IL-1 induce increased expression of adhesion molecules on vascular endothelial cells. For example, TNF-𝛼 stimulates the expression of E-selectin, a molecule of endothelial adhesion that binds adhesion molecules to neutrophils selectively. IL-1 induces increased ICAM-1 and VCAM-1 expression, which binds to lymphocyte and monocyte integrins.

10. Neutrophils, monocytes, and lymphocytes circulating identify these adhesion molecules on the walls of the blood vessels, bind to them and then pass into the tissue spaces via the vessel wall.

11. IL-1 and TNF-𝛼 also act on macrophages and endothelial cells to induce the development of chemokines that, by increasing their adhesion to vascular endothelial cells and by acting as potent chemotactic factors, contribute to the influx of neutrophils.

12. Besides, macrophages and neutrophils are activated by IFN-𝞬 and TNF-𝛼, facilitating increased phagocytic activity and increased release of lytic enzymes into tissue areas.

13. Without the overt intervention of the immune system, a local acute inflammatory response may occur.

14. Cytokines released at the inflammation site also promote both the adherence of immune system cells to vascular endothelial cells and their migration into tissue spaces through the vessel wall.

15. This results in an influx of lymphocytes, neutrophils, monocytes, eosinophils, basophils, and mast cells to the tissue damage site, where these cells are involved in antigen clearance and tissue healing.

To monitor tissue damage and promote the tissue repair processes that are important for healing, the length and strength of the local acute inflammatory response must be carefully controlled. TGF-β has been shown to play an essential role in limiting the response to inflammation. It also encourages fibroblast aggregation and proliferation and the deposition of an extracellular matrix necessary for proper tissue repair. Clearly, in the inflammatory response, the leukocyte adhesion processes are of great importance. As exemplified by leukocyte-adhesion deficiency, a failure of proper leukocyte adhesion may result in disease.

SYSTEMIC ACUTE-PHASE RESPONSE:

The systemic response is known as the acute-phase response accompanies the local inflammatory response. This response is characterised by fever induction, increased hormone synthesis such as ACTH and hydrocortisone, increased white blood cell development (leukocytosis), and the production of a large number of liver acute-phase proteins.

1. The rise in body temperature prevents a variety of pathogens from rising and tends to strengthen the immune response to the pathogen.

2. A prototype acute-phase protein whose serum level increases 1000-fold during an acute-phase response is a C-reactive protein.

3. It is made up of five similar polypeptides by noncovalent interactions kept together.

4. The C-reactive protein binds and activates complements to a wide range of microorganisms, resulting in the accumulation of opsonin C3b on the surface of microorganisms.

5. The C3b-coated microorganisms can then readily phagocytose phagocytic cells, which express C3b receptors.

6. The combined activity of IL-1, TNF-𝛼 and IL-6 is linked to several systemic acute-phase effects. To cause a fever response, each of these cytokines works on the hypothalamus.

7. Increased levels of IL-1, TNF- and IL-6 (as well as leukaemia inhibitory factor (LIF) and oncostatin M (OSM)) induce hepatocyte development of acute-phase proteins within 12–24 h of the onset of acute-phase inflammatory response.

8. To induce colony-stimulating factors (M-CSF, G-CSF, and GM-CSF) secretion, TNF-𝛼 also acts on vascular endothelial cells and macrophages.

9. These CSFs induce hematopoiesis, causing the number of white blood cells required to combat the infection to increase temporarily.

10. Redundancy in the capacity of at least five cytokines (TNF-𝛼, IL-1, IL-6, LIF, and OSM) to induce liver acute-phase protein development results from the induction of NF-IL6, a common transcription factor, after the receptor interacts with each of these cytokines.

11. Amino-acid sequencing of cloned NF-IL6 showed that it has a high degree of sequence identity with C / EBP, a liver-specific transcription factor.

12. NF-IL6 and C / EBP both contain a leucine-zipper domain and a simple DNA-binding domain, and in the promoter or enhancer of the genes encoding different liver proteins, both proteins bind to the same nucleotide sequence.

13. C / EBP, which stimulates albumin and transthyretin production, is hepatocyte-constitutively expressed.

14. Expression of NF-IL6 increases and that of C / EBP decreases as an inflammatory response arises, and the cytokines interact with their respective receptors on liver hepatocytes.

15. The inverse relationship between these two transcription factors reflects the observation that serum protein levels such as albumin and transthyretin decrease during an inflammatory response while those of acute-phase proteins increase.

LEUKOCYTE MIGRATION AND INFLAMMATION

BY: SAI MANOGNA (MSIWM014)

Many leukocyte forms shift from one part of the body to the next. It refers primarily to lymphocytes that circulate in the blood and lymph continuously and travel through other types of leukocytes into the tissues at sites of infection or tissue damage. Not only does this recirculation increase the probability that lymphocytes specific to a specific antigen will encounter that antigen, but it is also crucial for inflammatory response development. The complex response to local injury or other damage is inflammation; it is characterised by redness, heat, swelling, and pain. Various immune system cells and various mediators are involved in inflammation. Without the regulated movement of leukocyte populations, assembling and controlling inflammatory responses would be difficult.

Recirculation of Lymphocytes:

1. Lymphocytes are capable of a remarkable recirculation stage, continually flowing to the different lymphoid organs via the blood and lymph.

2. Almost 45% of all lymphocytes are transferred directly from blood to spleen after a short transit period of approximately 30 minutes in bloodstream, where they live for approximately five hours.

3. Nearly identical numbers of lymphocytes (42%) exit from the blood into separate peripheral lymph nodes, where they live for about 12 hours.

4. A smaller number of lymphocytes of about 10% move into tertiary extra lymphoid tissues by crossing between endothelial cells that line the capillaries.

5. Typically, these tissues have few, lymphoid cells, but during an inflammatory response, they will import them.

6. Skin, pulmonary and genitourinary tract, and various mucosal epithelia of the gastrointestinal, interface with the external environment are known as immunologically active tertiary extra lymphoid tissues.

Mechanism:

1. The mechanism of continuous lymphocyte recirculation causes the antigen to be identified in the maximum number of antigenically committed lymphocytes.

2. An individual lymphocyte can make a complete circuit as much as 1-2 times per day from blood to tissues and back to lymph.

3. Since a particular antigen is recognised by only about one in 10⁵ lymphocytes, a large number of T or B cells will tend to have affected the antigen in a given antigen-presenting cell within a short period in order to produce a specific immune response.

4. By thorough recirculation of lymphocytes, the small percentage of lymphocytes committed to a given antigen makes contact with that antigen when its presence is increased.

5. Factors that control, coordinate, and direct the circulation of lymphocytes and antigen-presenting cells also increase the probability of such contacts profoundly.

Cell Adhesion Molecules (CAMs):

The vascular endothelium controls the passage of blood-borne molecules and leukocytes into the tissues as an essential “gate-keeper.” The cells have to bind to and migrate between the endothelial lining cells of the blood vessels, in order for circulating leukocytes to penetrate inflamed tissue or peripheral lymphoid organs. This mechanism is called extravasation.

1. Endothelial cells release CAMs unique to the leukocyte.

2. Some of these membrane proteins are constitutively expressed; others are only expressed as a response to local cytokine concentrations generated during an inflammatory response.

3. Lymphocytes, monocytes, and granulocytes that recirculate carry receptors that bind to vascular endothelium CAMs, allowing these cells to extravasate into the tissues.

4. CAMs on leukocytes often help to increase the strength of functional interactions between immune system cells. They also play their role in adhesion of leukocyte to vascular endothelial cells.

5. It has been shown that different adhesion molecules contribute to the interaction between Th and B cells, Th and APCs, and CTLs and target cells.

6. A variety of CAMs of endothelial and leukocyte have been cloned and characterised, giving new information about the mechanism of extravasation.

7. Most of these CAMs belong to four protein families: the family of selectin, the family of mucin, the family of integrin, and the superfamily of immunoglobulin (Ig).

Mucin-like CAMs	Selectins	Ig superfamily CAMs	Integrins
GlyCam-1 CD34 PSGL-1 MAdCAM-1	L-selectin P-selectin E-selectin	ICAM-1,2,3 VCAM-1 LFA-2 (CD2) LFA-3 (CD58) MAdCAM-1	α4β1 (VLA-4, LPAM-2) α4β7 (LPAM-1) α6β1 (VLA-6) α Lβ 2 (LFA-1) α Mβ 2 (Mac-1) α Xβ 2 (CR4, p150/95)

SELECTINS:

1. The membrane glycoprotein selectin family has a distal lectin-like domain that allows these molecules to attach to particular groups of carbohydrates.

2. Selectins mainly interact with sialylated carbohydrate moieties, also associated with mucin-like molecules.

3. Three molecules named L, E, and P are part of the selectin family.

4. Most circulating leukocytes express L-selectin, while vascular endothelial cells express E-selectin and P-selectin.

5. The Selectin molecules are responsible for the initial vascular endothelium stickiness of leukocytes.

MUCINS:

1. Mucins are a group of strongly glycosylated serine- and threonine-rich proteins. 2. Their extended structure enables selectins to be presented by sialylated carbohydrate ligands.

3. For instance, sialylated carbohydrates on two mucin-like molecules (CD34 and GlyCAM-1) expressed on specific endothelial cells of lymph nodes are recognised by L-selectin on leukocytes.

4. The mucin-like molecule which is PSGL-1 found on neutrophils interacts with the inflamed endothelium expressed by E- and P-selectin.

INTEGRINS:

1. The integrins are heterodimeric proteins that are expressed by leukocytes consisting of ⍺ and β chain which promote both vascular endothelium adherence and other cell-to-cell interactions.

2. Integrins are classified according to which they comprise a subunit.

3. Different integrins are expressed by different leukocyte populations, allowing these cells to bind to various CAMs along the vascular endothelium which belong to the immunoglobulin superfamily.

3. Some integrins are activated before they bind to their ligands with high affinity.

4. Leukocyte-adhesion deficiency (LAD), and an autosomal recessive disorder shows the significance of integrin molecules in leukocyte extravasation.

5. It is characterised by repeated infections with bacteria and delayed wound healing.

ICAMS:

1. Several adhesion molecules contain a variable number of domains identical to immunoglobulins and are thus categorised within the superfamily of immunoglobulins.

2. ICAM-1, ICAM-2, ICAM-3 and VCAM, which are expressed in vascular endothelial cells and bind to different integrin molecules.

3. Both Ig-like domains and mucin-like domains have an essential cell-adhesion molecule called MAdCAM-1.

4. This molecule is expressed in the endothelium of the mucosa and directs the entry of lymphocytes into the mucosa.

5. It binds to integrins through its domain-like immunoglobulin and selectins through its domain-like mucin.

Extravasation of Neutrophils:

Different cytokines and other inflammatory mediators act upon the local blood vessels by which an inflammatory response develops, inducing increased expression of endothelial CAMs. It is then said to activate or inflame the vascular endothelium. The first cell type of binding to inflamed endothelium and extravasate into the tissues is usually neutrophils. Neutrophils must identify the inflamed endothelium and bind tightly enough so that the flowing blood does not sweep them away. The endothelial layer must then be penetrated by the attached neutrophils and migrate into the underlying tissue. By a similar mechanism, monocytes and eosinophils extravasate, but the best steps for the neutrophil have been identified, so here we concentrate on neutrophils.

It is possible to divide the neutrophil extravasation process into four sequential steps:

(1) rolling processes,

(2) activation by the stimulation of the chemoattractant,

(3) arrest and accession,

(4) migration of transendothelial.

Mechanism:

1. In the first step, via a low-affinity selectin-carbohydrate interaction, neutrophils bind loosely to the endothelium.

2, Cytokines and other mediators act upon the local endothelium during an inflammatory response, inducing expression of the selectin family’s adhesion molecules.

3. These E- and P-selectin molecules bind on the neutrophil membrane or with a sialylated lactose aminoglycan called sialyl Lewis to mucin-like cell-adhesion molecules.

4. This interaction briefly tethers the neutrophil to the endothelial cell, but soon the neutrophil is detached by the sheer force of the circulating blood.

5. Selectin molecules tether the neutrophil on another endothelial cell; this process is replicated so that the neutrophil tumbles end-over-end around the endothelium. This form of binding called rolling

6. different chemoattractants activate it as the neutrophil rolls; these are either permanent features of the surface of the endothelial cell or secreted locally by cells involved in the inflammatory response.

7. Members of a broad family of chemoattractive cytokines called chemokines are amongst the chemoattractants. Interleukin 8 (IL-8) and the macrophage inflammatory protein (MIP-1) are two chemokines involved in the activation process. Not all chemoattractants belong to the category of chemokines.

8. Other chemoattractants include platelet-activating factor (PAF), split-complement products such as C5a, C3a, and C5b67, and various N-formyl peptides produced during infection by breaking down bacterial proteins.

9. Binding to receptors on the neutrophil membrane of these chemoattractants triggers an activating signal mediated by receptor-associated G proteins.

10. This signal causes the integrin molecules in the neutrophil membrane to change conformationally, increasing their affinity with the endothelium Ig-superfamily adhesion molecules.

11. Subsequent contact between integrins and CAMs of the Ig superfamily stabilises the neutrophil’s adhesion to the endothelial cell, making it possible for the cell to bind tightly to the endothelial cell.

12. The neutrophil subsequently migrates into the tissues via the vessel wall.

The further steps in transendothelial migration and how it is guided are still largely unknown; they can be mediated by further activation or by a separate migration stimulus by chemoattractants and subsequent integrin-Ig-superfamily interactions.