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The Human Immune System Seen from a Biomedical Engineering Viewpoint
Published in Robert B. Northrop, Endogenous and Exogenous Regulation and Control of Physiological Systems, 2020
Antigens (Ag) are by definition molecules that elicit an immune response in the body. They are generally proteins and polysaccharides. Nonprotein molecules called haptens can cause an immune response as well. This response is generally thought to be due to the hapten reacting chemically with certain tissue molecules; the product of the reaction is the antigen. Antigens can be of exogenous or endogenous origin. Exogenous antigens can be inhaled proteins from animal dander, pollen, or mold spores. Exogenous antigens can also be eaten; nuts and shellfish are common foods to which people are allergic. Another route for internalization of antigens is through the skin and mucus membranes. These can include injected antigens such as used in allergy desensitization, pollen injected by a thorn stick, bacteria entering through a cut or abrasion, parasites that are injected by insects or that burrow into the skin, and poison ivy oil. Proteins from the cell walls of internalized bacteria, viruses, spirochetes, parasitic worms, etc. can activate immune responses.
Bioaerosol-Induced Hypersensitivity Diseases
Published in Harriet A. Burge, Bioaerosols, 2020
Cory E. Cookingham, William R. Solomon
The nature of antigen. An antigen is a substance that is specifically recognized by the immune system, with development of specific antibody, specifically reactive cells, or both. Antigenic agents are principally proteins, but polysaccharides, nucleic acids, and lipids may elicit immune responses. Highly reactive small molecules (called haptens) can also induce an immune response after attachment to a larger (protein) molecule. The dinitrophenol (DNP) group is a good example of a hapten. Biogenic antigens are usually complex molecules such as glycoproteins with molecular weights 10,000 to greater than 100,000 Da (Goodman, 1991). The size of an antigen may affect the type of immune response elicited. Stupp et al. (1971) demonstrated this by immunizing guinea pigs with DNP attached to varying numbers of lysine molecules. When only two lysine residues were attached, humoral (circulating antibody) immunity alone was stimulated, while the production of humoral and cellular immunity required at least eight lysine residues conjugated to DNP.
Basic Chemical Hazards to Human Health and Safety — II
Published in Jack Daugherty, Assessment of Chemical Exposures, 2020
Antigens are substances that activate specific defenses. Antigens are large molecules of protein, or a protein component called glycoprotein or lipoprotein, whole cells, or viruses containing proteins. One of these proteins produced by a specific immune response is called an antibody for that response, and antibodies may or may not stimulate production of additional antibodies. Antigens called haptens are incomplete antibodies that have only one antigenic determinant site and cannot stimulate a complete immune response, unless they bind with molecules that have second antigenic determinant sites. Activated lymphocytes mount a direct attack on the antigens. Lymphocyte-produced antibodies then attack the antigens. These attacks are called cellular immunity and humoral immunity respectively.
A β-galactosidase-expressing E. coli culture as an alternative test to identify skin sensitizers and non-sensitizers
Published in Journal of Toxicology and Environmental Health, Part A, 2018
Mahesh Raj Nepal, Youra Kang, Mi Jeong Kang, Doo Hyun Nam, Tae Cheon Jeong
Cells, either primitive or mammalian, exhibit a complex nature (Kroy 2017). In the process of chemical-mediated skin sensitization, the antigenic adducts of a hapten along with an endogenous carrier are presented by skin dendritic cells to induce hapten-specific proliferation of T cells (Agüero et al., 2012). Haptens are non-immunogenic, low-molecular-weight chemicals that bind via their electrophilic residues to the nucleophilic part of carrier molecules, predominantly epidermal peptides and proteins (Kimber et al. 2002). Therefore, the reactivity of skin-sensitizing haptens with certain proteins may be incorporated into a bacterial system. Consequently, reactive sensitizers are able to interact with certain proteins resulting in altered expression of specific genes, including β-galactosidase. The cell surface and inside of bacteria are complex and consist of a variety of macromolecules including proteins and polysaccharides (Facey and Kuhn 2004). These macromolecules exhibit numerous types of molecular interactions with environmental toxins and chemicals producing alterations in biological and cellular functions, as evidenced by interaction between sensitizers and carrier proteins during skin sensitization (Papanastasiou et al. 2013; Watson 2015). In an E. coli culture expressing β-galactosidase mediated by LacZ gene, one of the consequences of molecular interaction of E. coli with chemically reactive skin sensitizers is inhibition or suppression of β-galactosidase enzyme activity attributed to altered functional aspect of LacZ gene (Bitton and Koopman 1992). When the expression of β-galactosidase is turned on by IPTG treatment, the rapid production of proteins including β-galactosidase might be more vulnerable to the toxic insult initiated by sensitizers. Therefore, it was of interest to try the possible applicability of E. coli system in detecting skin sensitizers, similar to the well-known Ames test for assessing mutagenicity of test chemicals employed in classifying chemicals with carcinogenic potential. The aim of this study was to utilize a β-galactosidase-expressing E. coli culture to identify and classify chemicals based upon skin sensitizing and non-sensitizing potential.