Inflammation and the immune system

Published on 23/06/2015 by admin

Filed under Complementary Medicine

Last modified 22/04/2025

Print this page

rate 1 star rate 2 star rate 3 star rate 4 star rate 5 star
Your rating: none, Average: 0 (0 votes)

This article have been viewed 1646 times

Chapter 30 Inflammation and the immune system

Chapter contents

Origins of the immune system 223
The function of the immune system 223
Why is an anti-inflammatory response necessary? 224
Components of the immune system 224
How does the immune system work? 225
The inflammatory system 227
Proteins involved in the inflammatory and immune systems 230
Anti-inflammatory medication 230

It is difficult to separate the immune system from the anti-inflammatory system; the two are interrelated and any defect in the immune system has far-reaching effects on a patient’s health.

To properly understand the immune system it is necessary to have a reasonable understanding of its working components. The explanation here is very simplified but is more than adequate for the scope of the book and for a basic understanding of the underlying principles of the complicated processes of the immune and anti-inflammatory systems.

Origins of the Immune System

Communication in early evolution was cell to cell. This means of communication survived as we evolved to become the immune system and the inflammatory response.

The Function of the Immune System

The immune system is the body’s defence system against bacteria, fungi, parasites, viruses and other pathogens entering the body. It is also a means of eliminating these pathogens before they cause serious harm.

The construction of the immune system allows it to adapt so as to mount a more rapid and vigorous attack each time it encounters a particular pathogen.

Why is An Anti-Inflammatory Response Necessary?

The anti-inflammatory response is a defensive response to tissue injury or damage. It is designed to remove the irritant and repair damaged tissue.

Components of the Immune System

Leucocytes

Leucocytes – white blood cells – are part of the body’s mobile defence system. There are five types of white blood cell:

• Neutrophils
• Eosinophils
• Basophils

image Granulocytes produced in bone marrow; 6-day supply in the marrow.
• Lymphocytes: continually in the circulatory and lymph systems. Produced mainly in the lymph system (lymph glands, spleen, thymus tonsils, etc.).
• Monocytes: change to macrophages after entering the tissues.

• Neutrophils

• Respond to the chemicals released by bacteria and dead tissue cells, moving to the area of highest concentration.
• Phagocytose the foreign cells and destroy them.
• Die soon after phagocytosis, as the process uses up their glycogen reserves. The dead neutrophils accumulate, with tissue fluid, to create pus.

• Eosinophils

• Increase in allergic reactions.
• Increase in most parasitic infections.
• Have surface receptors for immunoglobulin E (IgE).

• Basophils

• Similar to mast cells but mobile.
• Highly specific receptors to IgE (see mast cells, below).

• Lymphocytes

• Increase in viral infections.
• Two major types: B and T lymphocytes.

• Monocytes

• Leave the bloodstream to become tissue macrophages, which remove dead cell debris. Also attack some bacteria and fungi (neutrophils do not deal with these effectively).
• Have a longer life than neutrophils as they are able to replace their digestive enzymes.

Other Components

• Mast Cells

• Found in connective tissue and contains granules of histamine (p. 175) and heparin (see Figure 28.2, p. 213).
• Involved in wound healing and defence against pathogens.
• Involved in allergic (Chapter 34 ‘Respiratory diseases’, p. 267) and anaphylactic reactions.
• Highly specific receptors to IgE.

How Does the Immune System Work?

Pathogens that invade the body stimulate the immune system, which has three main stages of response:

1. To neutralize the pathogen by:

• secreting cytotoxic proteins: proteins lethal to pathogens
• phagocytosis: engulfing the pathogen and effectively digesting it.

2. To fragment the pathogen by phagocytosis: the fragments are presented on the surface of antigen-presenting cells (APCs) in the lymph tissue and provide a marker that enables the cells of the immune system to recognize that type of pathogen. The APCs also release a cytokine (interleukin-1; see below), which encourages the proliferation of B and T cells.
3. To secrete interleukins: the above stimulates the cells of the immune system to secrete interleukins, which further stimulate the immune system. The B and T lymphocytes are cloned in the lymph nodes. Some cells produce a pool of memory cells (M) specific to a particular antigen, which will enable the body to respond much faster with another exposure. This takes place in the lymph node and is known as the induction phase. The other cells go on to the effector phase.

The effector phase is one of the following:

• Humoral-mediated phase: involves antibodies, which act in the fluid of the blood and tissues to involve the B cells. There is also some added stimulation from interaction between the B cells and T helper cells.
• Cell-mediated phase: this works where the antibodies cannot reach, deals with pathogens in cells and involves the T cells.

Humoral Response

A humoral-mediated response (Figure 30.1):

• Is an immediate reaction. Hence the speed of anaphylactic shock, hay fever, asthma and some food allergies. It is a type 1 reaction.
• The T helper cells not only activate B cells but also release interleukins (signalling molecules and part of a group classed as cytokines). These interleukins stimulate eosinophils, mast cell production and the generation of IgE, which are the mediators in chronic inflammation.
• IgE has a strong tendency to attach to mast cells and basophils, changing the composition of their cell membranes so that they release their contents. People with atopic allergies have high levels of IgE in their blood.
• Some of the components are histamine, protease, platelet-activating factors, etc., which open-up the local blood vessels, attracting the eosinophils and neutrophils to the site. The eosinophils and neutrophils attack and destroy bacteria. The site is also damaged by the contents such as the proteases. There is loss of fluid into the tissues and contraction of the local smooth muscles.
image

Figure 30.1 Humoral (antibody)-mediated response showing points of immunosuppressant intervention.

Antibodies or immunoglobulins (hence the shorthand Ig) have two main functions:

1. To recognize and interact specifically with particular antigens (Figure 30.2): this can provide some damage limitation.
2. To activate the immune system: the tails act as a tag to activate the complement sequence (see below).
image

Figure 30.2 Structure of an antibody showing its attachment to antigens.

There are five classes of antibody: IgA, IgD, IgE, IgG and IgM.

• The Complement System

This is similar in mechanism to the coagulation cascade (see Figure 28.1, p. 212). It is activated by interaction in several ways:

• Antigen–antibody complex (classical pathway)
• the antigen (alternative pathway)
• complex carbohydrates (see Chapter 9 ‘Carbohydrates’ p. 71).

The final part of complement activation produces a membrane attack complex, which creates holes in the outer membrane of Gram-negative bacteria (see Figure 29.1, p. 218).

The complement cascade has a feedback mechanism, which in theory should limit its action. However, several of the products of the complement cascade are powerful inflammatory stimulants, so it is possible for the inflammatory response to get out of hand.

image

Figure 30.3 Diagram demonstrating the cell-mediated response showing points of immunosuppressant interventions.

Cell-Mediated Response (Figure 30.3)

• T cells move to an inflammatory area.
• Two types of T cell are involved: cytotoxic T cells, which ensure the death of a cell displaying a foreign antigen, and T helper cells, which assist the immune response.
• This response is not as well understood as the humoral response and is considerably more complex.
• This is a delayed reaction (possibly a few days).
• The absence of T helper cells means that the immune system is virtually unable to function.
• Type IV hypersensitivity: e.g. the tuberculin reaction – this is one example of a delayed response.
• Rheumatoid arthritis (RA), multiple sclerosis and insulin-dependent diabetes are all examples of cell-mediated response conditions.

The Inflammatory System

The Inflammatory Response

The inflammatory response occurs in the following way:

• Vasodilatation of the local blood vessels increases the local blood flow.
• Increased permeability of the capillaries allows leakage of large amounts of fluid into the interstitial spaces.
• Clotting of the fluid in the interstitial spaces due to excessive amounts of fibrinogen and other proteins leaking from the capillaries.
• Migration of large numbers of neutrophils, basophils, monocytes and eosinophils into the tissues.
• Swelling of the tissue cells.

An inappropriate cell-mediated immune response is stimulated and there is infiltration of mononuclear (cells with one nucleus, e.g. lymphocytes, as opposed to polymorphonuclear cells, e.g. neutrophils) cells and release of various cytokines.

Inflammation can continue after it is needed if the pathogen or antigen persists. Hence, a practitioner can see this lingering for weeks, months or years. Chronic inflammation is the result of the type IV cell-mediated immune response and chronic autoimmune diseases are therefore thought to be due to the reaction initially set off by a pathogen.

Inappropriate T-cell activity underlies all types of hypersensitivity.

Components Involved in Inflammation

• Eicosanoids

The name implies molecules derived from 20-carbon essential fatty acids. These are usually omega 3 and omega 6 essential fatty acids. The main source of eicosanoids is arachidonic acid. There are four types of eicosanoid (Figure 30.4):

image

Figure 30.4 Various eicosanoids.

• prostaglandins PG)
• prostacyclins
• thromboxanes

image Prostanoids.
• leukotrienes: found in inflammatory exudates. Present in rheumatoid athritis, psoriasis and ulcerative colitis. Potent spasmogens causing contraction of the bronchioles.

Prostaglandins

• Prostaglandins (PG) are active in very low hormone level concentrations.
• Can regulate blood pressure, smooth muscle contraction, gastric secretions and platelet aggregation.
• Generated from phospholipids. Very important in the anti-inflammatory system.
• Are produced by cyclo-oxygenase (COX) enzymes. There are two pathways: COX- 1 and COX-2.

Prostaglandin PGE1

• Causes vasodilatation.
• Prevents platelet aggregation.
• Anti-inflammatory effect.
• Increased synthesis useful.
• Formed from a precursor of arachidonic acid.

Prostaglandin PGE2

• Biphasic action: although largely thought of as a vasoconstrictor, PGE2 is also a powerful vasodilator, therefore encouraging a greater blood supply to that area and more histamines and inflammatory components. The histamines then increase the inflammatory problem.
• Proinflammatory.
• Formed from arachidonic acid.

Prostaglandin PGE3

• Prevents platelet aggregation.
• Anti-inflammatory effect.
• Formed from eicosapentoic acid (EPA).

Prostacyclins

• Inhibit platelet aggregation.
• Inhibit vasoconstriction.

Thromboxanes

• Vasoconstrictors, therefore hypertensive agents (see Chapter 26 ‘Cardiovascular disorders’, p. 195).
• Facilitate aggregation of platelets: aspirin works by inhibiting the COX enzyme responsible for producing thromboxanes (see Figure 30.5), thus preventing platelet aggregation.
image

Figure 30.5 The prostaglandin and leukotriene production pathway, demonstrating points of intervention.

Leukotrienes

• Leukotrienes are synthesized from arachidonic acid, by a lipoxygenase found in leucocytes and macrophages.
• Leukotrienes act on G protein receptors (see Figure 19.5, p. 141).
• Involved in asthmatic and allergic reactions.
• Sustain inflammatory reactions.
• Increase vascular permeability.
• Encourage leucocyte chemotaxis (i.e. the movement of leucocytes towards an area of inflammation).

Proteins Involved in the Inflammatory and Immune Systems

Cytokines

• Regulate inflammatory and immune reactions.
• Interleukins are a form of cytokine.
• Interferons are a form of cytokine that has antiviral activity.

• Tumour Necrosis Factor Alpha (TNF-Alpha)

• TNF-alpha is a cytokine that is important in the inflammatory response.
• Induces the synthesis of interleukins.
• Macrophages, mast cells and activated T cells secrete TNF-alpha.
• Stimulates macrophages to produce cytotoxic metabolites thus increasing the activity of phagocytes.
• TNF-alpha been implicated in rheumatoid arthritis and Crohn’s disease.

Anti-Inflammatory Medication

• Glucocorticoids.
• Non-steroidal anti-inflammatories.

Glucocorticoids (Corticosteroids)

• Steroids are normally produced by the adrenal glands and are made and released as required.
• Cholesterol is the framework from which steroids are made. Steroids produced by the body will have an anti-inflammatory action and immunosuppressive effects.
• Used in serious cases of inflammation, e.g. rheumatoid arthritis, ulcerative colitis or chronic active hepatitis.

Prednisolone is a commonly used oral steroid.

• Adverse Effects

The adverse effects of corticosteroids are tied up with the hormonal system, which in its natural state is a delicate balance of hormonal interactions with the various glands in the body.

• Metabolic effects: rounded, ‘moon face’; deposits of fat creating a buffalo hump; obesity of the trunk leaving thin arms and legs; a tendency to bruising; possible diabetes; muscular weakness.
• Fluid retention and possible hypertension.
• Osteoporosis (see Chapter 37 ‘Metabolic disorders’, p. 290).
• Might get a sense of euphoria, but might also get mood swings; the steroids can also precipitate a depressive illness.
• Cataracts: rare.
• Dyspepsia.
• Suppression of immune system leading to repeated infections.

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)

The anti-inflammatory effect of non-steroidal anti-inflammatories (NSAIDs) is due to inhibition of the COX enzyme (Figure 30.5). These drugs have three major effects:

• anti-inflammatory
• analgesic
• antipyretic.

• Anti-Inflammatory Effect

Different NSAIDs work on different COX enzymes (Figure 30.6):

• Indometacin, aspirin: COX-1.
• Diclofenac, naproxen: equal effect on COX-1 and COX-2.
• Piroxicam, ibuprofen, mefenamic acid: less selective.
image

Figure 30.6 The structure of various anti-inflammatories, including the natural anti-inflammatory agent gingerol (note the similarity in structure to ibuprofen and aspirin). NSAI = non-steroidal anti-inflammatories.

Although the NSAIDs reduce inflammation, the mechanism is still not well understood.

• Analgesic Effect

PGE1 and PGE2 sensitize pain fibres to bradykinin or 5-hydroxytryptamine. Blocking their production will reduce this effect.

• Antipyretic Effect

NSAIs reset the internal thermostat when there is a fever. This is thought to be the result of prostaglandin production by the hypothalamus.

• Adverse Effects

• Gastrointestinal effects (diarrhoea, nausea, vomiting, dyspepsia): due to direct mucosal irritation or because of inhibition of the synthesis of the prostaglandins that normally inhibit acid secretion, as well as protecting the gut layer. This problem was thought to have been overcome with the development of COX-2 inhibitors, which, because they were more specific for the COX-2 pathway, allowed the COX-1 pathway to function, thus reducing the incidence of mucosal irritation. However, widespread usage found a link with increased myocardial infarction when COX-2 inhibitors were taken continuously for 18 months. This is thought to be the result of an imbalance in the thromboxane and prostacyclin levels, which might lead to an increase in platelet aggregation, one of the factors involved in blood haemodynamics.
• Skin: mild rashes, urticaria and photosensitivity.
• Lungs: can cause difficulties in breathing with asthmatics.
• Kidneys: can cause renal insufficiency. PGE2 involved in renin–angiotensin system.

• Aspirin

Aspirin is a derivation of salicylates, which are found naturally occurring in willow bark, meadowsweet, etc. Salicylic acid and acetyl salicylic acid (aspirin) were among the earliest drugs synthesized.

Adverse Effects

• Aspirin can irritate the lining of the gut and cause bleeding (Note: willow bark, meadowsweet and other salicylate-containing herbs are used by Western herbalists to help heal stomach ulcers).
• Some patients are allergic to salicylates.
• Can bring on or make asthma worse.
• Can cause serious imbalance in warfarin levels as aspirin is more favourably bound to plasma proteins than warfarin (see Chapter 16 ‘How do drugs get into cells?’, p. 126), thus releasing more free warfarin into the blood.

Immunosuppressants

• Prevent tissue rejection in organ transplants.
• Used in autoimmune diseases, e.g. rheumatoid arthritis, systemic lupus erythematosus.
• Used in certain types of cancer.

In a normal person, the T cells are largely responsible for killing the cells of an organ transplant or graft (e.g. following bone marrow transplantation), so their suppression – far more than the plasma antibodies – is a priority in treatment.

There is an overlap between pure immunosuppressant drugs and chemotherapy (see Chapter 39 ‘Chemotherapy’, p. 309). Immunosuppressant drugs are used at much lower doses than for chemotherapy. They require lifelong use.

Approaches to Suppression of the Immune System

• Suppression of growth of lymphatic tissue due to inhibition of gene expression: glucocorticoids.
• Use of cytotoxic agents to deplete expanding lymphocyte populations: antimetabolites (azathioprine), methotrexate (see Figure 39.2, p. 311) and alkylating agents (cyclophosphamide) to suppress the formation of antibodies and T cells.
• Inhibition of lymphocyte signalling to block activation and production of lymphocytes: ciclosporin (specific for T cells and does not affect other parts of the immune system).
• Inhibition of cytokines (interleukins and TNF) essential for mediating the immune response: TNF-alpha inhibitor.
• Use of antibodies to deplete the immune system of specific cells: used for prevention and treatment of organ transplant rejection.

• Glucocorticoids

• Suppress the growth of lymphoid tissue and, as a result, decrease the formation of both antibodies and T cells.
• Inhibit the production of inflammatory mediators, including platelet-activating factor, leukotrienes, prostaglandins, histamine and bradykinin.
• Work both as immunosuppressives and anti-inflammatories, therefore useful for conditions such as rheumatoid arthritis.

Adverse Effects

See p. 230.

• Cytotoxic Agents

• Alkylating agents: used to treat some types of glomerulonephritis caused by a systemic inflammatory condition, e.g. systemic lupus erythematosus.
• Antimetabolics (antiproliferative): azathioprine suppresses the formation of antibodies and T cells by mimicking a purine.

• Inhibition of Lymphocyte Signalling

Ciclosporin

• Fat-soluble antibiotic of fungal origin.
• Impairs production and release of interleukins, which activate T-cell growth, and so prevents T-cell activation. Specificity to T cells means that other parts of the immune system are left intact.

Adverse Effects

• Nephrotoxicity.
• Hypertension: might require medication to lower blood pressure.
• Possible convulsions.
• Tremor.
• Possible nausea, vomiting or anorexia.
• Hyperglycaemia.
• Hyperlipidaemia.
• Liver dysfunction.
• Hirsutism.
• Potential for serious drug, herb and supplement interactions.

• Inhibition of cytokines

TNF-Alpha Inhibitors

• Bind to TNF-alpha blocking its action.
• Have been used in the treatment of rheumatoid arthritis.

Adverse Effects

• Possibility of increased infection and malignancy.
• Injection-site reactions.

• Interleukin Inhibitors

• Have been used in rheumatoid anthritis.
• Possibility of increased infection and malignancy.
• Injection-site reactions.

As TNF-alpha and interleukins are very close in action, therapy using the combination of the two is being investigated.

• Use of Antibodies to Deplete the Immune System of Specific Cells

• Used for prevention and treatment of organ transplant rejection.
• Batches vary in efficacy and toxicity.

Adverse Effects

• Fevers and chills.
• Possible hypotension.
• Glomerulonephritis.

A combination of immunosuppressant drugs might be used.

Immunostimulants

Used in immunodeficiency and some cancers.

Interferons

• Immune-enhancing properties.
• Increase antigen presentation.
• Macrophage, natural killer cell and cytotoxic T lymphocyte activation.
• Used mainly as therapeutic agents with melanoma, renal cell carcinoma and chronic myelogenous leukaemia.

Adverse Effects

• Fever, chills and general malaise.
• Myalgias.
• Myelosuppression.
• Headache.
• Depression.

Related posts:

Default ThumbnailToxicology Respiratory diseases Analgesia and relief of pain Isomers Terpenes Phenols