* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Specificity of primary and secondary responses
Lymphopoiesis wikipedia , lookup
Vaccination wikipedia , lookup
Gluten immunochemistry wikipedia , lookup
Sociality and disease transmission wikipedia , lookup
Social immunity wikipedia , lookup
Complement system wikipedia , lookup
Multiple sclerosis research wikipedia , lookup
Autoimmunity wikipedia , lookup
Hepatitis B wikipedia , lookup
Anti-nuclear antibody wikipedia , lookup
Sjögren syndrome wikipedia , lookup
Adoptive cell transfer wikipedia , lookup
Innate immune system wikipedia , lookup
Duffy antigen system wikipedia , lookup
Immune system wikipedia , lookup
Molecular mimicry wikipedia , lookup
Immunocontraception wikipedia , lookup
Hygiene hypothesis wikipedia , lookup
Adaptive immune system wikipedia , lookup
DNA vaccination wikipedia , lookup
Cancer immunotherapy wikipedia , lookup
Immunosuppressive drug wikipedia , lookup
Monoclonal antibody wikipedia , lookup
Lec ( 5 ) Immunology Immune response Difference between Primary and Secondary Immune Response! Imagine a person is never exposed to a particular immunogen. For the first time in his life one antigen enters into his body (this event is called Priming). This leads to a relatively week, short-lived immune responses called Primary immune responses. The primary immune responses can be divisible into four phases (lag phase, exponential phase, steady state phase, and declining phase) (Fig. 7.1). a. The lag (latent) phase is the period from the initial exposure of immunogen to the time of detection of antibodies (In humans the average time of lag phase is about one week). During this lag phase specific T cells and B cells are activated by their contact with immunogen. b. The exponential phase is the period during which there is a rapid increase in antibody levels due to secretion of antibodies by many plasma cells. c. After the exponential phase the antibody level remains relatively at a constant level because the secretion and degradation of antibodies occur almost at equal rates. This phase is called steady state phase (plateau phase). d. Afterwards the antibody level gradually declines (declining phase) because new plasma cells are no longer produced and the existing plasma cells are dying. This generally indicates Lec ( 5 ) Immunology that the immunogen has been eliminated from the body and consequently there is no stimulus for continued antibody production. When a similar antigen enters the host for the second and subsequent times, the immune responses induced are called secondary immune responses. During secondary immune responses the lag period is shortened and antibody level reaches a very high steady state level within few days. Since the secondary immune responses are induced rapidly (within a short time after the entry of the antigen) to greater levels, the antigen is eliminated before it can cause damage or disease. More over the antibodies remain in circulation for a longer period. The secondary immune responses are also called anamnestic immune responses. (Amnesia = forget; anamnesis = don’t forget, remember). Since specific memory T and B cells for the immunogen have already been produced during the primary response, the lag phase is shorter when compared to the primary immune response. Comparison between Primary and Secondary Immune Response Primary Immune Response Secondary Immune Response After initial exposure to a foreign antigen, there is a lag phase where B cells are differentiating into plasma cells, but not yet producing antibodies. Antibody generation can take anything from 2 days to several months. If a previously encountered antigen enters the body again, a few days up to several years later, a secondary immune response develops. This time, the lag phase is greatly reduced, to about 3-4 days. Low quantities of antibodies are normally secreted. High levels of antibodies are produced. After a while, the amount of antibody decreases to minimal levels. Antibody levels remain elevated for longer. Antibodies are mostly IgM, but some IgG antibodies are produced. IgGs are the main antibody secreted, with some small amounts of IgM sometimes. Lec ( 5 ) Immunology GENERAL CHARACTERISTICS OF THE ANTIBODY RESPONSE Self / non-self-discrimination One characteristic feature of the specific immune system is that it normally distinguishes between self and non-self and only reacts against non-self. Memory A second feature of the specific immune response is that it demonstrates memory. The immune system "remembers" if it has seen an antigen before and it reacts to secondary exposures to an antigen in a manner different than after a primary exposure. Generally only an exposure to the same antigen will illicit this memory response. Lec ( 5 ) Immunology Specificity A third characteristic feature of the specific immune system is that there is a high degree of specificity in its reactions. A response to a particular antigen is specific for that antigen or a few closely related antigens. Fate of the immunogen 1-Clearance after primary injection. The kinetics of antigen clearance from the body after a primary administration is depicted in Figure 1. Equilibrium phase The first phase is called the equilibrium or equilibration phase. During this time the antigen equilibrates between the vascular and extravascular compartments by diffusion. This is normally a rapid process. Since particulate antigens don't diffuse, they do not show this phase. Catabolic decay phase In this phase the host's cells and enzymes metabolize the antigen. Most of the antigen is taken up by macrophages and other phagocytic cells. The duration will depend upon the immunogen and the host. Immune elimination phase In this phase, newly synthesized antibody combines with the antigen producing antigen/antibody complexes which are phagocytosed and degraded. Antibody appears in the serum only after the immune elimination phase is over. Lec ( 5 ) Immunology 2- Clearance after secondary injection If there is circulating antibody in the serum, injection of the antigen for a second time results in a rapid immune elimination. If the is no circulating antibody then injection of the antigen for a second time results in all three phases but the onset of the immune elimination phase is accelerated. Specificity of primary and secondary responses Antibody elicited in response to an antigen is specific for that antigen, although it may also cross react with other antigens which are structurally similar to the eliciting antigen. In general secondary responses are only elicited by the same antigen used in the primary response. However, in some instances a closely related antigen may produce a secondary response, but this is a rare exception.