Atopyis defined as the tendency of an individual to produce IgE antibodies in response to various environmental antigens and thus develop strong immediate hypersensitivity (allergic) responses. Individuals with allergies to environmental antigens (e.g., pollen, house dust) are atopic.
Localized anaphylaxis involves reactions limited to a specific target tissue or organ and often involves epithelial surfaces at the site of allergen entry. Atopy is thus defined as the tendency to manifest localized anaphylactic reactions, and this tendency is inherited.
Atopic allergies include a wide range of IgE-mediated disorders, including allergic rhinitis (hay fever), asthma, atopic dermatitis (eczema), and food allergies.
Allergic Rhinitis:
This is commonly known as “hay fever” and results from the reaction of airborne allergens with the sensitized mast cells in the conjunctivae and nasal mucosa, which induces the release of pharmacologically active mediators from mast cells. The mediators thus cause localized vasodilation and increased capillary permeability. The symptoms of allergic rhinitis usually include watery exudation of the conjunctivae, upper respiratory tract and nasal mucosa, and sneezing and coughing.
Asthma:
Asthma, a common manifestation of localized anaphylaxis, is triggered by degranulation of mast cells with the release of mediators, but instead of occurring in the nasal mucosa, the reaction develops in the lower respiratory tract. This results in the contraction of the bronchial smooth muscles and thus eventually leads to broncho-constriction.
Food Allergies:
A variety of foods can induce localized anaphylaxis in allergic individuals. In addition, localized smooth-muscle contraction and vasodilation can be induced by allergen cross-linking of IgE on mast cells along the upper or lower gastrointestinal tract resulting in symptoms such as vomiting or diarrhea.
Atopic Dermatitis:
Atopic dermatitis (allergic eczema) is an inflammatory disease of the skin frequently associated with a family history of atopy. This disease is observed most commonly among young children, often developing during infancy. Serum IgE levels are often elevated, and the allergic individual develops erythematous skin eruptions filled with pus.
Article by- SAMPRATI PAREKH (MSIWM049)
References:
Cellular and Molecular Immunology by Abul K. Abbas – 7thEdition
A brief overview of the infections of the respiratory tract and its pathogens:
The respiratory tract along with the gastrointestinal tracts is one of the major connections between the interiors of the body and the outside environment.
The respiratory tract is the pathway is that pathway of the body through which fresh oxygen enters the body and removes the excess carbon dioxide which is not needed by the body.
Anatomy of the respiratory system:
Broadly, the respiratory system of humans can broadly be divided into two distinct areas; the upper and the lower respiratory tracts.
The parts that consist the lower respiratory tract are:
Trachea
Bronchi, and
Bronchioles
The respiratory pathway begins with the nasal and the oral passages. These passages serve to humidify the air that is inspired. These pathways extend past the nasopharynx and the oropharynx to the trachea and then to the lungs.
The trachea is the organ that divides into the bronchi, which then further subdivides into the bronchioles. The bronchioles are the smallest branches of the trachea which finally terminate into the alveoli.
Approximately 300 million alveoli are said to present in the lungs. These mainly serve as the primary, microscopic, gas exchange structures of the respiratory tract.
The lungs (along with the respiratory system) and the heart lie in the thoracic cavity.
The thoracic cavity has three partitions that are separated from one other by the pleura (the pleura majorly cushions the lungs and reduce the friction which may develop between the lungs, rib cage and the chest cavity. It is a two layered membrane covering the lungs.)
The lungs occupy the right and the left pleural cavity while the mediastinum (the space between the right and the left lungs) is occupied by the esophagus, trachea, large blood vessels along with the heart.
Pathogenesis of the respiratory tract:
The success of an organism to cause disease is mainly dependent on the organism’s ability to cause disease (pathogenesis), and
The human hosts ability to prevent the infection (strength of the host’s immune system)
The host factors that help in non-specifically protect the respiratory tract from infection are:
Nasal hair
Convoluted passages and the mucous lining of the nasal turbinate
Secretory IgA and non-specific antibacterial substances (like lysozyme) in respiratory secretions
The cilia and the mucous lining of the trachea and reflexes such as coughing and sneezing.
In addition to the non-specific hosts defenses, normal flora of the nasopharynx and the oropharynx help in the prevention of colonization of the upper respiratory tract.
Microorganism factors:
Organisms possess certain traits that promote colonization leading to infection in the host. The factors that influence the respiratory tract infections are –
Adherence:
The potential of a microorganism depends, in one way or the other, on its ability to establish a stable contact/foothold on the surface of the host by the process of adherence.
The ability of microorganisms to adhere to the host surface is dependent on two factors:
Presence of normal flora, and
Overall state of the host.
Surviving or growing on host tissue without causing harmful effects is called colonization.
Most etiologic agents must first adhere to the mucosa of the respiratory tract to some extent before they can cause harm.
Example: Streptococcus pyogenes possess specific adherence factors and its gram-positive cell wall contains lipoteichoic acids and M proteins. Many gram-negative bacteria like Enterobacteriaceae, Pseudomonas spp., Bordetella pertussis, adhere by the means of proteinaceous fingerlike projections called fimbriae.
Viruses possess either a hemagglutinin or other proteins that mediate that epithelial attachment.
Toxins:
Certain microorganisms are considered to be etiologic agents of disease because they possess virulence factors that are expressed in every host.
Example: Corynebacterium diphtheriae.
Some strains of Pseudomonas aeruginosa also produce toxins which are similar to the toxins of Diphtheria.
Bordetella pertussis which is the causative agent of whooping cough produces toxins that play a role in inhibiting the activity of phagocytic cells and damaging the cells of the respiratory tract.
Microorganism growth:
Pathogens cause disease by merely growing in the host tissue, interfering with normal tissue function and attracting host immune effectors, such as neutrophils and macrophages.
Example: S. pyogenes, M. tuberculosis, Mycoplasma pneumoniae, etc.
Avoiding the Host Response:
Certain respiratory tract pathogens possess the ability to evade host defense mechanisms.
S. pneumoniae, H. influenza, K. pneumoniae and others possess polysaccharide capsules that serve both to prevent engulfment by phagocytic host cells and to protect somatic antigens from being exposed to host immunoglobulins.
Organisms of the respiratory tract and agents that cause diseases:
Pathogens may or may not cause the respiratory infection but can be present as a part of normal flora.
Some of the pathogens that exist and results in the respiratory infection are referred to as true pathogens.
Some of the pathogens that are present in the body but never cause an infection until and unless they are met with the favorable conditions are called
as opportunistic pathogens.
Possible pathogen: they are the pathogens that are likely to cause respiratory
infections.
Example: Actinomyces spp., Haemophilus influenzae, Enterobacteriaceae, etc.
Rare pathogen: pathogens that may cause a respiratory infection are rare
pathogens. Example: Coxiella burnetti, Brucella spp., Salmonella spp, etc.
Definite respiratory pathogen: pathogens that always cause respiratory infections are called as definite respiratory pathogens.
Example: Bordetella pertussis, Blastomyces dermatitidis, Legionella spp., etc.
Different types of agents that cause respiratory diseases are bacteria, fungi or
viruses.
Bacterial agents: the bacterial agents that cause respiratory infections are
Mycoplasma spp., Streptococcus pneumoniae and Neisseria meningitides.
Fungal agents: the fungal agents that cause respiratory infections are Candida
albicans, Cryptococcus neoformans and Histoplasma capsulatum.
Viral agents: the viral agents that cause respiratory infections are human
metapneumovirus, adenovirus, enteroviruses, and herpes simplex virus.
Major respiratory diseases are caused by M. tuberculosis, S. pyogenes and
K.pneumonia.
Sources:
Foundations in Microbiology, Author: Kathleen Park Talaro, Barry Chess
Immunology is the branch of science dealing with the study of immunity. Louis Pasteur is considered as the Father of Immunology.
HISTORY OF IMMUNOLGY
Immunology started from the observation of people who recovered from certain infectious diseases and who never got infected with the same.
The earliest written evidence on immunology is by Thucydides during 430 BC .He was describing about a plague in Athens where he mentioned that people who recovered from plague could only nurse the sick because they won’t get the disease again.
The first recorded attempt was by Chinese and turks in the 15 century. Dried crusts of from smallpox pustules was inhaled through nostrils or inserted into cuts in the skin. They used in this technique called variolation to prevent the deadly and fatal smallpox.
Variolation technique was later improved by Edward Jenner in 1718.
Next major advancement was that success of Louis Pasteur in growing bacterium responsible for fowl cholera in chicken. After completing, he concluded that ageing weekend the virulence of pathogen. He called the attenuated strain as vaccine .he named it so in honor of Jenner’s technique of cowpox inoculation.
Next decade various researchers demonstrated that an active component from the serum of immune animals are capable neutralizing toxins, precipitating toxins and occlude rich bacteria. They were termed as angio toxin precipitating and agglutinating respectively. Gamma –globulin present in serum is responsible for this activities. This active molecule is called as antibody.
DIFFERENT TYPES OF IMMUNE RESPONSE
Inherent Immunity
It’s a first line of defense mechanism and non-specific. Inherent immunity include physical barriers (e.g., skin, saliva etc.)and cells (e.g. Macrophages, neutrophils, basophils, mast cells etc.).It is active for first few days during infection period.
Adaptive Immunity
It is the second line of defense. It responds to anything that is foreign and also remembers it.It involves antibodies and lymphocytes. Active and passive immunity comes under Acquired immunity
ANTIGEN
It can be any substance that can be recognized by immunoglobulin receptor of B-cells or by the T-cell receptor when complexes with MHC. Antigens include toxins, bacteria, foreign blood and the cells of transplanted organs.
TYPES OF ANTIGENS
Exogenous Antigen: Antigens that have entered the body from outside either by inhalation, ingestion or injection .Immune response to these antigens is often sub-clinical. Some Exogenous Antigen later become endogenous Antigens.
Endogenous Antigens: They are generated within an individual normal cells as a result of cell metabolism. Endogenous antigens include xenogenic, autologous and idiotypic antigens.
Tumour Antigens: They are present on the surface of tumor cells. They can sometimes be presented only by tumour cells and never by the normal ones due to some tumour specific mutations, such antigens are called Tumour specific Antigens (TSAs).Commonly these antigens are presented by both tumour cells and normal cells, and they are called Tumour Associated Antigens.
ANTIBODIES (IMMUNOGLOBULINS)
They are group of glycoproteins which are present in the serum and tissue fluids of all mammals. They are produced by the immunocompetent B-cells called as plasma cells .Some of these antigen-binding proteins are carried on the surface of B-cells, where they act as receptors for specific antigens and thus, confers antigenic specificity on B-cells.
Structure of Antibodies: It is Y-shaped in appearance whose arms can swing at an angle of 180 degree. It consist of two identical light chains and heavy chains which are linked by disulphide bonds and non-covalent interactions such as hydrogen bonds, salt bridges and hydrophobic bonds in the form of heterodimer.
TYPES OF ANTIBODIES
Immunoglobulin G (IgG): It is a major immunoglobulin present in serum. It is the major Ig produced during the secondary response. It is the only Ig which can cross placenta. It also helps in the activation of classical compliment pathway.
Immunoglobulin A (IgM): It accounts for approximately 5%-10% of the total serum immunoglobulin with an average serum concentration of 1.5 mg/mL is the first immunoglobulin to be synthesized by the newborn. It is confined to the intravascular pool only. IgM are capable of agglutinating the antigen as well as it can neutralize the viral particles.IgM is also more efficient activator of the classical complement pathway.
Immunoglobulin a (IgA): It constitutes only 10%-15% of the total immunoglobulin in serum. It served as a first line of defense against the microbial invasion at the mucosal surfaces. Secretory IgA present in breast milk protect the newborn against infection during the first month of life.
Immunoglobulin E (IgE): It’s present in extremely low in serum. It mediate the immediate hypersensitivity reactions or allergic reactions. On the exposure of allergen, IgE will be produced which binds to Fc receptors present on the membranes of blood basophils and tissue mast cells. It also plays a major role in parasitic infections
Immunoglobulin D (IgD): It constitutes only 0.2% of the total immunoglobulin in serum. It is expressed by mature B-cells on its surface together with IgM.
SCOPE OF IMMUNOLOGY
Immunology is a diverse and growing discipline. It plays an important role in the development vaccines. Immunology is associated with the treatment of allergy and asthma. It plays a major role in the disciplines of medicine especially for organ transplantation, oncology, virology, bacteriology. Immunoinformatics is special stream which link immunology and bioinformatics.Majorily for vaccine design.
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