BOOKS4BIO

The immune system in mammals is capable of producing a seemingly unlimited number of antibodies that can react with the millions of antigens we potentially encounter in our lifetimes. This genetic diversity is a key to the effective protection of our bodies against pathogens that are constantly evolving new antigen molecules. Does the cell have million of genes to create all this variability? This was one early theory, but given the small number of genes in the human (about 30,000), it is clear that this cannot be the case. Antibody diversity was difficult to understand until researchers realized that eukaryotic genes are formed by remarkable recombination events. The essence of the current theory of antibody diversity is that the genes responsible for the synthesis of a particular antibody are not contiguous units, but are assembled from clusters of gene fragments present in regions of the DNA. One section of these gene fragments codes for the constant region of the antibody,

Immunogenicity is determined by – 1. Foreignness – An antigen must be a foreign substance to the animal to elicit an immune response. 2. Molecular Size – The most active immunogens tend to have a molecular mass of 14,000 to 600,000 Da. Examples: tetanus toxoid, egg albumin, thyroglobulin are highly antigenic. Insulin (5700) is either non-antigenic or weekly antigenic. 3. Chemical Nature and Composition – In general, the more complex the substance is chemically the more immunogenic it will be. Antigens are mainly proteins and some are polysaccharides. It is presumed that presence of an aromatic radical is essential for rigidity and antigenicity of a substance. 4. Physical Form – In general particulate antigens are more immunogenic than soluble ones. Denatured antigens are more immunogenic than the native form. 5. Antigen Specificity – Antigen specificity depends on the specific actives sites on the antigenic molecules (Antigenic determinants). Antigenic determinants o

Antigen is a substances usually protein in nature and sometimes polysaccharide, that generates a specific immune response and induces the formation of a specific antibody or specially sensitized T cells or both. Although all antigens are recognized by specific lymphocytes or by antibodies, only some antigens are capable of activating lymphocytes. Molecules that stimulate immune responses are called Immunogens. Epitope is immunologically active regions of an immunogen (or antigen) that binds to antigen-specific membrane receptors on lymphocytes or to secreted antibodies. It is also called antigenic determinants. Auto-antigens, for example, are a person’s own self antigens. Examples: Thymoglobulin, DNA, Corneal tissue, etc. Alloantigens are antigens found in different members of the same species (the red blood cell antigens A and B are examples). Heterophile antigens are identical antigens found in the cells of different species. Examples: Forssmann antigen, Cross-re

The first human vaccines against viruses were based using weaker or attenuated viruses to generate immunity. The smallpox vaccine used cowpox, a poxvirus that was similar enough to smallpox to protect against it but usually didn’t cause serious illness. Rabies was the first virus attenuated in a lab to create a vaccine for humans. Vaccines are made using several different processes. They may contain live viruses that have been attenuated (weakened or altered so as not to cause illness); inactivated or killed organisms or viruses; inactivated toxins (for bacterial diseases where toxins generated by the bacteria, and not the bacteria themselves, cause illness); or merely segments of the pathogen (this includes both subunit and conjugate vaccines). S. No. Vaccine Vaccines of this type on U.S. Recommended childhood (ages 0-6) Immunization schedule 1 Live, attenuated Measles, mumps, rubella (MMR combined vaccine) Varicella