The Mechanisms Of Primary And Secondary Antibody

Published Date: 02 Nov 2017

Razieh Rezaei

Name: ______________________________________________

Master of Immunobiology

Program:_____________________________________________

GS34384Matriculation Number:________________________________________

2013

Humoral and cellular are the immune events that occur when an immunocompetent host encounters an antigen for the first time are the primary immune response. In addition to measurable immune products, the primary immune response generates memory cells. These memory cells contribute to the immune events, either humoral or cellular, that occur on second or subsequent exposure to an antigen the anamnestic (secondary) immune response. Antibody production occurs in four phases following antigen challenge: (1) a lag phase when no antibody is detectable: (2) a log phase in which the antibody titer rise logarithmically: (3) a plateau phase during which the antibody titer remains steady: and (4) a decline phase during which antibody levels gradually decline as a result of catabolism and decreased production.

Kinetics of antibody responses to T-dependent Antigen

Primary Antibody response: Figure 1 is demonstrated the kinetics of a primary antibody response to an antigen.

Inductive, latent or lag phase: In lag phase, the antigen is identified as foreign agent and the cells start to proliferate and differentiate in response to the antigen. The duration of this phase will depend on the antigen and it is usually 5 to 7 days.

Log or Exponential Phase: In log phase, the concentration of antibody exponentially increases since the B cells were stimulated by the antigen differentiate into plasma cells that secrete antibody.

Plateau or steady-state phase: In plateau phase, antibody decay is balanced antibody synthesis therefore there is no net raising antibody concentration.

Decline or decay phase: In decline phase, the antibody degradation rate exceeds which of antibody synthesis and the level of antibody decreases. Finally, the level of antibody may reach base line levels.

Fig. 1 Fig.2

Secondary, memory response (Figure 2)

Lag phase: there is a lag phase in a secondary respond and it is generally shorter than that declared in a primary response.

Log phase: The log phase is faster and higher antibody levels are obtained in a secondary response.

Plateau phase: The plateau levels of antibody are much greater in the secondary immune response.

Decline phase: The decline phase is not as a fast phase but antibody may insist for months, years or even during a lifetime.

Specificity of primary and secondary responses

The same antigen in the primary response is only elicited Secondary responses. Nevertheless, in some cases a closely related antigen may produce a secondary response, but this is an unusual exception.

Qualitative changes in antibody during primary and secondary responses

Immunoglobulin class variation: IgM is the major class of antibody produced in the primary response whereas IgG (IgA or IgE) is in the secondary response. The IgG antibodies are persisted in the secondary response.

Antibody affinity and avidity: in the primary immune response, the antibodies formed early normally have a low affinity for their respective antigens. In the secondary immune response the affinity of antibody for antigen is increased greatly. The IgG antibody produced affinity increases progressively during the response, especially after low doses of antigen. This is referred to as affinity maturation. Affinity maturation is most declared after secondary challenge with antigen. As a result of enhanced affinity, the avidity of the antibodies raises during the response.

Cross-reactivity: The higher affinity later in the response, there is also a growth in detectible cross reactivity. If a minimum affinity of 10-6 is needed to discover a reaction, early in an immune response the reflex of a cross reacting antigen in an affinity of 10-3 will not be discovered.

.

Cellular events during primary and secondary responses to T-dependent antigen

Primary response

Lag phase: Clones of T and B cells with the proper antigen receptors bind antigen, become activated and start to proliferate. The widened clones of B cells differentiate into plasma cells that start to secrete antibody.

Log phase: In the first, the plasma cells secrete IgM antibody since the Cμ heavy chain gene is near to the reorganized VDJ gene. Finally some B cells switch from producing IgM to IgG, IgA or IgE. Since most of the B cells proliferate and differentiate into antibody secreting cells the antibody density enhances exponentially.

Stationary phase: Since antigen is exhausted, T and B cells are no longer activated. Furthermore, the mechanisms which down regulate the immune response come into play. Moreover, plasma cells start to die. When the antibody synthesis rate equals the antibody decay rate the stationary phase is achieved.

Decline phase: Whereas there is no new antibody is produced due to the antigen is no longer present to activate T and B cells and also the residual antibody slowly is decreased, the decay phase is achieved.

Secondary response: Not all of the T and B cells that are aroused by antigen during primary encounter with antigen die. Some of T and B cells are long lived cells and constitute what is mention to as the memory cell pool. Both memory T cells and memory B cells are constructed and memory T cells survive more than memory B cells. Upon secondary challenge against antigen not only are new T and B cells stimulated, the memory cells are also stimulated and therefore there is a shorter lag phase in the secondary response. Since there is a widened clone of cells being aroused the rate of antibody production is also enhanced during the log phase of antibody production and more levels are achieved. Since plenty if not all of the memory B cells will have changed to IgG (IgA or IgE) production, IgG is constructed earlier in a secondary response. Moreover since there is a widened clone of memory T cells that can help B cells to switch to IgG (IgA or IgE) production, the predominant class of Ig constructed after secondary challenge is IgG (IgA or IgE).

Ab response to T-independent antigen: Reactions to T-independent antigen are determined by the production of approximately exclusively IgM antibody and no secondary response.

Class switching: During an antibody respond to a T-dependent antigen a switch happen in the class of Ig constructed from IgM to some other class (except IgD). Our comprehending of the structure of the immunoglobulin genes helps describe how class switching occurs.

Membrane and secreted immunoglobulin: The membrane immunoglobulin has identical specificity on a B cell and the Ig secreted by the plasma cell progeny of a B cell.