Since its first publication in 1929, Topley & Wilson’s Microbiology & Microbial Infections has grown from one to eight volumes, a reflection of the ever-increasing breadth and depth of knowledge in each of the areas covered. The tenth edition continues the tradition of providing the most comprehensive available reference on microorganisms and related infectious diseases. The new edition of Topley & Wilson’s Microbiology & Microbial Infections is an essential addition to the bookshelves of medical microbiologists, immunologists, infectious disease specialists and public health professionals, as well as being a standard reference for specialists within the pharmaceutical industry, trainees across the medical sub-specialities, and laboratory technicians.
The 10th edition features:
the latest information on epidemiology, identification, classification, and new and emerging infections, all supported by the basic science that underlies infectious disease
each volume includes the best writing in the fields of Bacteriology, Virology, Medical Mycology, Parasitology, and Immunology
a new Immunology volume – both a complement to the other titles, and an excellent reference work for every immunologist
fully integrated colour for the first time – the text is supported by over 1,400 photographs and 700 line drawings
an international, acclaimed editorial team and a highly respected group of over 400 contributors, drawing on best practice from over 20 countries
a comprehensive cumulative index
The 10th edition of Topley & Wilson’s Microbiology & Microbial Infections is an essential addition to the bookshelves of medical microbiologists, immunologists, infectious disease specialists, pathologists, travel and tropical medicine specialists, and public health scientists; and will also be a standard reference for all those working in the pharmaceutical industry, trainees across the medical subspecialties, and laboratory technicians. The breadth of information available in the tenth edition is astonishing, and will support academic and clinical practice for many years to come.
Topley and Wilson’s Microbiology and Microbial Infections, 8 Volume Set, 10th Edition
Roitt’s Essential Immunology has established itself as the book of choice for students of immunology worldwide. This excellent textbook is commonly regarded as ‘the best of the immunology primers’ and the eleventh edition remains at the cutting edge of this fascinating area of science. The trademark of Roitt’s Essential Immunology is its highly readable content, emphasis on core knowledge and excellent four-colour artwork; thoroughly revised and redrawn for this new edition. The text covers key information needed by students of medicine and immunology, including:
* The basis of immunology
* The recognition of antigen
* Technology
* The acquired immune response
* Immunity to infection
* Clinical immunology
Roitt’s Essential Immunology is also supported by a website at www.roitt.com which includes interactive MCQs for each chapter with feedback on all answers selected, animations showing key concepts and database of figures, further reading and useful links.
The only textbook written for undergraduates by teachers of the course, this bestseller presents the most current concepts in an experimental context, conveying the excitement of scientific discovery, and highlighting important advances while providing unsurpassed pedagogical support for the first-time learner. The new edition is thoroughly updated, including most notably a new chapter on innate immunity, a capstone chapter on immune responses in time and space, and many new focus boxes drawing attention to exciting clinical, evolutionary, or experimental connections that help bring the material to life. Table of Contents
Part I Introduction
1. Overview of the Immune System
2. Cells, Organs, and Microenvironments of the Immune System
3. Receptors and Signaling: B and T Receptors
4. Receptors and Signaling: Cytokine and Chemokine
Part II Innate Immunity
5. Innate Immunity
6. The Complement System
Part III Adaptive Immunity: Antigen receptors and MHC
7. Organization and Expression of Lymphocyte Receptor Genes
8. The Major Histocompatibility Complex and Antigen Presentation
Part IV Adaptive Immunity: Development
9. T-Cell Development
10. B-Cell Development
Part V Adaptive Immunity: Effector Responses
11. T-cell Activation, Differentiation, and Memory
12. B-cell Activation, Differentiation, and Memory
13. Effector Responses: Cell and Antibody-Mediated Immunity
14. Immune Responses in Time and Space
Part VI The Immune System in Health and Disease
15. Inflammation: Allergy and Hypersensitivities
16. Tolerance, Autoimmunity, and Transplantation
17. Infectious Diseases and Vaccines
18. Immunodeficiency Disorders
19. Cancer and the Immune System
Part VII Experimental Methods
20. Experimental Methods
Review of Medical Microbiology and Immunology, Warren Levinson
Review of Medical Microbiology and Immunology, Warren Levinson
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Review of Medical Microbiology and Immunology, Warren Levinson
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To put your preparation for USMLE Step 1 and course exams on the fast track, only one resource will do: Review of Medical Microbiology and Immuniology. Completely updated throughout, the Eleventh Edition presents a high-yield review of the basic and clinical aspects of bacteriology, virology, mycology, parasitology, and immunology. Importantly, the book also emphasizes the real-world clinical application of microbiology and immunology to infectious diseases. One look, and you’ll see why it’s the defnitive microbiology course and exam quick review!
Everything you need to thoroughly and rapidly prepare for the exam!
More than 600 sample questions to test your knowledge
A complete USMLE-style exam with case-based questions
Review questions and case studies
Summaries of important microorganisms
Summary tables that emphasize the need-to-know aspects of infectious diseases
Basic science pearls that summarize fundamental concepts
Information-packed tables and figures
Pearls for the USMLE provide concise, valuable information for exams
70 color images, including Gram stains, bacteriological lab tests, viral electron micrographs and inclusion bodies, fungal stains, as well as protozoan and worm micrographs
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Here’s why this is THE definitive microbiology course and exam quick review (Condensed Table of Contents):
Basic Bacteriology, Clinical Bacteriology, Basic Virology, Clinical Virology, Mycology, Immunology, Ectoparasites, Brief Summaries of Medically Important Organisms, Clinical Cases, Pearls for the USMLE, USMLE (National Board) Practice Questions, USMLE (National Board) Practice Examination.
Review of Medical Microbiology and Immunology, Warren Levinson
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Kaplan USMLE Step 1 Lecture Notes 2009-2010: Anatomy, Behavioral Science, Biochemistry and Medical Genetics, Microbiology and Immunology, Pathology, Physiology, Pharmacology…
These books by Kaplan Medical reflect the new format of the test which is testing more clinically relevant concepts for Step 1 exam.
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Peptide hormones are proteins that have an effect on the endocrine system of animals.
Like other proteins, peptide hormones are synthesized in cells from amino acids according to mRNA transcripts, which are synthesized from DNA templates inside the cell nucleus. Preprohormones, peptide hormone precursors, are then processed in several stages, typically in the endoplasmic reticulum, including removal of the N-terminal signal sequence and sometimes glycosylation, resulting in prohormones. The prohormones are then packaged into membrane-bound secretory vesicles, which can be secreted from the cell by exocytosis in response to specific stimuli (e.g. --an increase in Ca2+ and cAMP concentration in cytoplasm).
These prohormones often contain superfluous amino acid residues that were needed to direct folding of the hormone molecule into its active configuration but have no function once the hormone folds. Specific endopeptidases in the cell cleave the prohormone just before it is released into the bloodstream, generating the mature hormone form of the molecule. Mature peptide hormones then travel through the blood to all of the cells of the body, where they interact with specific receptors on the surfaces of their target cells. Some peptide/protein hormones (angiotensin II, basic fibroblast growth factor-2, parathyroid hormone-related protein) also interact with intracellular receptors located in the cytoplasm or nucleus by an intracrine mechanism.
Notable peptide hormones
Several important peptide hormones are secreted from the pituitary gland. The anterior pituitary secretes three: prolactin, which acts on the mammary gland; adrenocorticotropic hormone (ACTH), which acts on the adrenal cortex to regulate the secretion of glucocorticoids; and growth hormone, which acts on bone, muscle, and the liver. The posterior pituitary gland secretes antidiuretic hormone, also called vasopressin, and oxytocin. Peptide hormones are produced by many different organs and tissues, however, including the heart (atrial-natriuretic peptide (ANP) or atrial natriuretic factor (ANF)) and pancreas (glucagon, insulin and somatostatin), the gastrointestinal tract (cholecystokinin, gastrin), and adipose tissue stores (leptin).
Some neurotransmitters are secreted and released in a similar fashion to peptide hormones, and some 'neuropeptides' may be used as neurotransmitters in the nervous system in addition to acting as hormones when released into the blood. When a peptide hormone binds to receptors on the surface of the cell, a second messenger appears in the cytoplasm, which triggers intracellular responses
Phagocytes are cells that protect the body by ingesting (phagocytosing) harmful foreign particles, bacteria, and dead or dying cells. Their name comes from the Greek phagein, "to eat" or "devour", and "-cyte", the suffix in biology denoting "cell", from the Greek kutos, "hollow vessel". They are essential for fighting infections and for subsequent immunity. Phagocytes are important throughout the animal kingdom and are highly developed within vertebrates. One litre of human blood contains about six billion phagocytes. They were first discovered in 1882 by Ilya Ilyich Mechnikov while he was studying starfish larvae.Mechnikov was awarded the 1908 Nobel Prize in Physiology or Medicine for his discovery. Phagocytes occur in many species; some amoebae behave like macrophage phagocytes, which suggests that phagocytes appeared early in the evolution of life.
Phagocytes of humans and other animals are called "professional" or "non-professional" depending on how effective they are at phagocytosis.The professional phagocytes include many types of white blood cells (such as neutrophils, monocytes, macrophages, mast cells, and dendritic cells).The main difference between professional and non-professional phagocytes is that the professional phagocytes have molecules called receptors on their surfaces that can detect harmful objects, such as bacteria, that are not normally found in the body. Phagocytes are crucial in fighting infections, as well as in maintaining healthy tissues by removing dead and dying cells that have reached the end of their lifespan.
During an infection, chemical signals attract phagocytes to places where the pathogen has invaded the body. These chemicals may come from bacteria or from other phagocytes already present. The phagocytes move by a method called chemotaxis. When phagocytes come into contact with bacteria, the receptors on the phagocyte's surface will bind to them. This binding will lead to the engulfing of the bacteria by the phagocyte. Some phagocytes kill the ingested pathogen with oxidants and nitric oxide. After phagocytosis, macrophages and dendritic cells can also participate in antigen presentation, a process in which a phagocyte moves parts of the ingested material back to its surface. This material is then displayed to other cells of the immune system. Some phagocytes then travel to the body's lymph nodes and display the material to white blood cells called lymphocytes. This process is important in building immunity. However, many pathogens have evolved methods to evade attacks by phagocytes.
A Southern blot is a method used in molecular biology for detection of a specific DNA sequence in DNA samples. Southern blotting combines transfer of electrophoresis-separated DNA fragments to a filter membrane and subsequent fragment detection by probe hybridization.
The method is named after its inventor, the British biologist Edwin Southern. Other blotting methods (i.e., western blot, northern blot, eastern blot, southwestern blot) that employ similar principles, but using RNA or protein, have later been named in reference to Edwin Southern's name. As the technique was eponymously named, Southern blot is capitalized as is conventional for proper nouns. The names for other blotting methods may follow this convention, by analogy
Method
Restriction endonucleases are used to cut high-molecular-weight DNA strands into smaller fragments.
The DNA fragments are then electrophoresed on an agarose gel to separate them by size.
If some of the DNA fragments are larger than 15 kb, then prior to blotting, the gel may be treated with an acid, such as dilute HCl. This depurinates the DNA fragments, breaking the DNA into smaller pieces, thus allowing more efficient transfer from the gel to membrane.
If alkaline transfer methods are used, the DNA gel is placed into an alkaline solution (typically containing sodium hydroxide) to denature the double-stranded DNA. The denaturation in an alkaline environment may improve binding of the negatively charged thymine residues of DNA to a positively charged amino groups of membrane, separating it into single DNA strands for later hybridization to the probe (see below), and destroys any residual RNA that may still be present in the DNA. The choice of alkaline over neutral transfer methods, however, is often empirical and may result in equivalent results.
A sheet of nitrocellulose (or, alternatively, nylon) membrane is placed on top of (or below, depending on the direction of the transfer) the gel. Pressure is applied evenly to the gel (either using suction, or by placing a stack of paper towels and a weight on top of the membrane and gel), to ensure good and even contact between gel and membrane. If transferring by suction 20X SSC buffer is used to ensure a seal and prevent drying of the gel. Buffer transfer by capillary action from a region of high water potential to a region of low water potential (usually filter paper and paper tissues) is then used to move the DNA from the gel on to the membrane; ion exchange interactions bind the DNA to the membrane due to the negative charge of the DNA and positive charge of the membrane.
The membrane is then baked in a vacuum or regular oven at 80 °C for 2 hours (standard conditions; nitrocellulose or nylon membrane) or exposed to ultraviolet radiation (nylon membrane) to permanently attach the transferred DNA to the membrane.
The membrane is then exposed to a hybridization probe—a single DNA fragment with a specific sequence whose presence in the target DNA is to be determined. The probe DNA is labelled so that it can be detected, usually by incorporating radioactivity or tagging the molecule with a fluorescent or chromogenic dye. In some cases, the hybridization probe may be made from RNA, rather than DNA. To ensure the specificity of the binding of the probe to the sample DNA, most common hybridization methods use salmon or herring sperm DNA for blocking of the membrane surface and target DNA, deionized formamide, and detergents such as SDS to reduce non-specific binding of the probe.
After hybridization, excess probe is washed from the membrane (typically using SSC buffer), and the pattern of hybridization is visualized on X-ray film by autoradiography in the case of a radioactive or fluorescent probe, or by development of color on the membrane if a chromogenic detection method is used.
Result
Hybridization of the probe to a specific DNA fragment on the filter membrane indicates that this fragment contains DNA sequence that is complementary to the probe. The transfer step of the DNA from the electrophoresis gel to a membrane permits easy binding of the labeled hybridization probe to the size-fractionated DNA. It also allows for the fixation of the target-probe hybrids, required for analysis by autoradiography or other detection methods. Southern blots performed with restriction enzyme-digested genomic DNA may be used to determine the number of sequences (e.g., gene copies) in a genome. A probe that hybridizes only to a single DNA segment that has not been cut by the restriction enzyme will produce a single band on a Southern blot, whereas multiple bands will likely be observed when the probe hybridizes to several highly similar sequences (e.g., those that may be the result of sequence duplication). Modification of the hybridization conditions (for example, increasing the hybridization temperature or decreasing salt concentration) may be used to increase specificity and decrease hybridization of the probe to sequences that are less than 100% similar.
Applications
Southern transfer may be used for homology-based cloning on the basis of amino acid sequence of the protein product of the target gene. Oligonucleotides are designed that are similar to the target sequence. The oligonucleotides are chemically synthesised, radiolabeled, and used to screen a DNA library, or other collections of cloned DNA fragments. Sequences that hybridise with the hybridisation probe are further analysed, for example, to obtain the full length sequence of the targeted gene. Second, Southern blotting can also be used to identify methylated sites in particular genes. Particularly useful are the restriction nucleases MspI and HpaII, both of which recognize and cleave within the same sequence. However, HpaII requires that a C within that site be methylated, whereas MspI cleaves only DNA unmethylated at that site. Therefore, any methylated sites within a sequence analyzed with a particular probe will be cleaved by the former, but not the latter, enzyme.
This mechanism allows killer T-cells to hunt down and destroy cells that are infected with germs or that have become cancerous. The other main type of T-cells are called helper T-cells. Helper T-cells orchestrate an immune response and play important roles in all arms of immunity.
In cell biology, phagocytosis (from Ancient Greek φαγεῖν (phagein) , meaning "to devour", κύτος, (kytos) , meaning "cell", and -osis, meaning "process") is the process by which a cell—often a phagocyte or a protist—engulfs a solid particle to form an internal vesicle known as a phagosome. Phagocytosis was revealed by Canadian physician William Osler[1] and later studed by Élie Metchnikoff.
Phagocytosis is a specific form of endocytosis involving the vesicular internalization of solids such as bacteria, and is therefore distinct from other forms of endocytosis such as the vesicular internalization of various liquids (pinocytosis). Phagocytosis is involved in the acquisition of nutrients for some cells. The process is homologous to eating at the level of single-celled organisms; in multicellular animals, the process has been adapted to eliminate debris and pathogens, as opposed to taking in fuel for cellular processes, except in the case of the animal Trichoplax.
In the immune system, phagocytosis is a major mechanism used to remove pathogens and cell debris. For example, when a macrophage ingests a pathogenic microorganism, the pathogen becomes trapped in a phagosome which then fuses with a lysosome to form a phagolysosome. Within the phagolysosome, enzymes and toxic peroxides digest the pathogen. Bacteria, dead tissue cells, and small mineral particles are all examples of objects that may be phagocytized.
Humoral immunity, also called the antibody-mediated beta cellularis immune system, is the aspect of immunity that is mediated by macromolecules (as opposed to cell-mediated immunity) found in extracellular fluids such as secreted antibodies, complement proteins and certain antimicrobial peptides. Humoral immunity is so named because it involves substances found in the humours, or body fluids.
The study of the molecular and cellular components that form the immune system, including their function and interaction, is the central science of immunology. The immune system is divided into a more primitive innate immune system, and acquired or adaptive immune system of vertebrates, each of which contains humoral and cellular components.
Humoral immunity refers to antibody production and the accessory processes that accompany it, including: Th2 activation and cytokine production, germinal center formation and isotype switching, affinity maturation and memory cell generation. It also refers to the effector functions of antibodies, which include pathogen and toxin neutralization, classical complement activation, and opsonin promotion of phagocytosis and pathogen elimination
Cell-mediated immunity is an immune response that does not involve antibodies, but rather involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen. Historically, the immune system was separated into two branches: humoral immunity, for which the protective function of immunization could be found in the humor (cell-free bodily fluid or serum) and cellular immunity, for which the protective function of immunization was associated with cells. CD4 cells or helper T cells provide protection against different pathogens. Cytotoxic T cells cause death by apoptosis without using cytokines, therefore in cell mediated immunity cytokines are not always present.
The innate immune system and the adaptive immune system each comprise both humoral and cell-mediated components.
Cellular immunity protects the body by:
activating antigen-specific cytotoxic T-lymphocytes that are able to induce apoptosis in body cells displaying epitopes of foreign antigen on their surface, such as virus-infected cells, cells with intracellular bacteria, and cancer cells displaying tumor antigens;
activating macrophages and natural killer cells, enabling them to destroy pathogens; and
stimulating cells to secrete a variety of cytokines that influence the function of other cells involved in adaptive immune responses and innate immune responses.
Cell-mediated immunity is directed primarily at microbes that survive in phagocytes and microbes that infect non-phagocytic cells. It is most effective in removing virus-infected cells, but also participates in defending against fungi, protozoans, cancers, and intracellular bacteria. It also plays a major role in transplant rejection.
The complement system is a part of the immune system that helps or complements the ability of antibodies and phagocytic cells to clear pathogens from an organism. It is part of the innate immune system,which is not adaptable and does not change over the course of an individual's lifetime. However, it can be recruited and brought into action by the adaptive immune system.
The complement system consists of a number of small proteins found in the blood, in general synthesized by the liver, and normally circulating as inactive precursors (pro-proteins). When stimulated by one of several triggers, proteases in the system cleave specific proteins to release cytokines and initiate an amplifying cascade of further cleavages. The end-result of this activation cascade is massive amplification of the response and activation of the cell-killing membrane attack complex. Over 30 proteins and protein fragments make up the complement system, including serum proteins, serosal proteins, and cell membrane receptors. They account for about 5% of the globulin fraction of blood serum and can serve as opsonins.
Three biochemical pathways activate the complement system: the classical complement pathway, the alternative complement pathway, and the lectin pathway.
Antigen processing is an immunological process that prepares antigens for presentation to special cells of the immune system called T lymphocytes. It is considered to be a stage of antigen presentation pathways. This process involves two distinct pathways for processing of antigens from an organism's own (self) proteins or intracellular pathogens (e.g. viruses), or from phagocytosed pathogens (e.g. bacteria); subsequent presentation of these antigens on class I or class II MHC molecules is dependent on which pathway is used. Both MHC class I and II are required to bind antigen before they are stably expressed on a cell surface. MHC I antigen presentation typically (considering cross-presentation) involves the endogenous pathway of antigen processing, and MHC II antigen presentation involves the exogenous pathway of antigen processing. Cross-presentation involves parts of the exogenous and the endogenous pathways but ultimately involves the latter portion of the endogenous pathway (e.g. proteolysis of antigens for binding to MHC I molecules).
While the conventional distinction between the two pathways is useful, there are instances where extracellular-derived peptides are presented in the context of MHC class I and cytosolic peptides are presented in the context of MHC class II (this often happens in dendritic cells).
An epitope, also known as antigenic determinant, is the part of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells. For example, the epitope is the specific piece of the antigen that an antibody binds to. The part of an antibody that binds to the epitope is called a paratope. Although epitopes are usually non-self proteins, sequences derived from the host that can be recognized (as in the case of autoimmune diseases) are also epitopes.
The epitopes of protein antigens are divided into two categories, conformational epitopes and linear epitopes, based on their structure and interaction with the paratope. A conformational epitope is composed of discontinuous sections of the antigen's amino acid sequence. These epitopes interact with the paratope based on the 3-D surface features and shape or tertiary structure of the antigen. The proportion of epitopes that are conformational is unknown.[citation needed]
By contrast, linear epitopes interact with the paratope based on their primary structure. A linear epitope is formed by a continuous sequence of amino acids from the antigen.
Human homeostasis (homeostasis is from Greek: ὅμοιος homoios, "similar" and στάσις stasis, "standing still") is the property of homeostasis within the human body.
The human body manages a multitude of highly complex interactions to maintain balance or return systems to functioning within a normal range. These interactions within the body facilitate compensatory changes supportive of physical and psychological functioning. This process is essential to the survival of the person and to our species. The liver, the kidneys, and the brain (hypothalamus, the autonomic nervous system and the endocrine system help maintain homeostasis. The liver is responsible for metabolizing toxic substances and maintaining carbohydrate metabolism. The kidneys are responsible for regulating blood water levels, re-absorption of substances into the blood, maintenance of salt and iron levels in the blood, regulation of blood pH, and excretion of urea and other wastes.
An inability to maintain homeostasis may lead to death or a disease, a condition known as homeostatic imbalance. For instance, heart failure may occur when negative feedback mechanisms become overwhelmed and destructive positive feedback mechanisms take over. Other diseases which result from a homeostatic imbalance include diabetes, dehydration, hypoglycemia, hyperglycemia, gout and any disease caused by the presence of a toxin in the bloodstream. Medical intervention can help restore homeostasis and possibly prevent permanent damage to the organs.
Type I hypersensitivity (or immediate hypersensitivity) is an allergic reaction provoked by reexposure to a specific type of antigen referred to as an allergen. Type I is not to be confused with Type II, Type III, or Type IV hypersensitivities.
Exposure may be by ingestion, inhalation, injection, or direct contact.
In type II hypersensitivity (or cytotoxic hypersensitivity) the antibodies produced by the immune response bind to antigens on the patient's own cell surfaces. The antigens recognized in this way may either be intrinsic ("self" antigen, innately part of the patient's cells) or extrinsic (adsorbed onto the cells during exposure to some foreign antigen, possibly as part of infection with a pathogen). These cells are recognized by macrophages or dendritic cells, which act as antigen-presenting cells. This causes a B cell response, wherein antibodies are produced against the foreign antigen.
An example of type II hypersensitivity is the reaction to penicillin wherein the drug can bind to red blood cells, causing them to be recognized as different; B cell proliferation will take place and antibodies to the drug are produced. IgG and IgM antibodies bind to these antigens to form complexes that activate the classical pathway of complement activation to eliminate cells presenting foreign antigens (which are usually, but not in this case, pathogens). That is, mediators of acute inflammation are generated at the site and membrane attack complexes cause cell lysis and death. The reaction takes hours to a day.
Type II reactions can affect healthy cells. Examples include Red blood cells in Haemolytic Anaemia, Acetylcholine receptors in Myasthenia Gravis, and TSH receptors in Grave's Disease.
Another example of type II hypersensitivity reaction is Goodpasture's syndrome where the basement membrane(containing collagen type IV) in the lung and kidney is attacked by one's own antibodies.
Another form of type II hypersensitivity is called antibody-dependent cell-mediated cytotoxicity (ADCC). Here, cells exhibiting the foreign antigen are tagged with antibodies (IgG or IgM). These tagged cells are then recognised by natural killer cells (NK) and macrophages (recognised via IgG bound (via the Fc region) to the effector cell surface receptor, CD16 (FcγRIII)), which in turn kill these tagged cells.
Type III hypersensitivity occurs when antigen-antibody complexes that are not adequately cleared by innate immune cells accumulate, giving rise to an inflammatory response and attraction of leukocytes.
Type 4 hypersensitivity is often called delayed type hypersensitivity as the reaction takes two to three days to develop. Unlike the other types, it is not antibody mediated but rather is a type of cell-mediated response.
CD4+ helper T cells recognize antigen in a complex with Class 2 major histocompatibility complex. The antigen-presenting cells in this case are macrophages that secrete IL-12, which stimulates the proliferation of further CD4+ Th1 cells. CD4+ T cells secrete IL-2 and interferon gamma, further inducing the release of other Th1 cytokines, thus mediating the immune response. Activated CD8+ T cells destroy target cells on contact, whereas activated macrophages produce hydrolytic enzymes and, on presentation with certain intracellular pathogens, transform into multinucleated giant cells.
