Types of acquired/adaptive/specific immunity
(A) Passive Humoral (antibodies) o (1) Natural Transfer of antibodies across the placenta or in the colostrum
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Cells of the immune system
Illustration of hematopoiesis
Source: Immunology, Goldsby et al., 5th edition (2002), WH Freeman
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Cells of the immune response
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Antigens/immunogens (contd..)
Antigen-binding site o The part of an antibody that binds antigen Antigenic determinant o A site on an antigen that stimulates an immune response o Also known as an epitope Antigen presenting cell (APC) o A cell that processes antigens and presents the peptides to T-cell receptor Antigen processing o The series of events that happen following antigen injection and antibody formation Antigenic shift o Changes over time in the surface antigens of some viruses
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Mode of action of adjuvants
1. By prolonging the retention of the antigen. 2. By promoting accumulation of immuno-reactive cells at the site of injection and in the draining lymph node. 3. By modifying the activities of cells that are concerned with generating, promoting and maintaining the immune response. 4. By modification of the presentation of the antigen to the immune system.
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Essential features of an antigen
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Factors affecting immunogenicity
Genetic composition of the animal o Species: man or mouse versus guinea pig for polysaccharide
Method of administration
o Dose o Mode: time and number of inoculation
o Route of administration
Adjuvants o A substance that, when administered with an antigen, enhances the immune response of that antigen
Polymorphonuclear leucocytes (granulocytes) o Neutrophils o Eosiniphils o Basophils Monocytes, macrophages and dendritic cells Lymphocytes and natural-killer (N-K) cells
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Tቤተ መጻሕፍቲ ባይዱings to consider when selecting an adjuvant
Routinely used adjuvants have side effects o Granulomas (lumps) at injection site
o Fever
o Arthritis (inflammation of joints) o Anterior uveitis (inflammation of eye structures – iris, ciliary body, etc.) Type of immune response required o Some adjuvants induce antibody responses, while some induce cell-mediated responses
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Ability to differentiate ‘self’ from ‘non-self’
T and B lymphocytes that are able to recognise ‘self’ antigens are usually removed during development Lymphocytes that react with ‘self’ antigens can be supressed by other cells Lymphocytes become unresponsive to activating stimuli – clonal anergy MHC plays a key role in differentiating ‘non self’ from ‘self’ Non response to self antigens is called self tolerance
Once there is a response, the hapten can bind to its antibody
Carrier o An immunogenic macromolecule to which a happen can bound, thus making the hapten immunogenic e.g. albumin Penicillin-albumin complex is responsible for allergy to penicillin in some individuals
Contain two types of enzyme rich granules
o Primary granules – myeloperoxidase, lysosome, elastase, hydrolase, cathepsin o Secondary granules – lysozyme, collagenase, lactoferrin
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Epitope or antigenic determinant
An epitope is a site on an antigen that stimulates an immune response There may be several epitomes in a complex antigen, but immune response to a particular epitope may be predominant – immunodominant epitope Conformational epitopes o Epitopes whose specificity is determined by shape of the antigen molecules Sequential epitopes o Epitopes whose specificity is determined by sequence of amino acids within the epitope
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Antigens/immunogens
Antigen o A molecule that can generate an immune response in an animal o A molecule that can react with pre-formed antibodies or primed Tcells Immunogen
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Some common adjuvants
1. Calmette and Guerin, the French scientists who developed the original BCG vaccine from an isolate of M. bovis in 1906.
o A substance that stimulates a strong immune response when introduced in an animal
The terms antigen or immunogen are often used interchangeably Antigenicity o The ability of a molecule to be recognised by a product of an immune response Immunogenicity o The ability of a substance to induce a detectable immune response