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<p>Plasma cells produced in the first immune response to an antigen are mainly of the class IgM whereas those produced from memory cells in the second immune response are mainly of the [[Immunoglobulin G - WikiBlood|IgG]] class.</p>
<p>Plasma cells produced in the first immune response to an antigen are mainly of the class IgM whereas those produced from memory cells in the second immune response are mainly of the [[Immunoglobulin G - WikiBlood|IgG]] class.</p>
<p>For more information on class switching click [[Immunoglobulins - WikiBlood#Immunoglobulin Class Switching|here]]</p>
<p>For more information on class switching click [[Immunoglobulins - WikiBlood#Immunoglobulin Class Switching|here]]</p>
==T-Cell Dependent and Independent Responses==
There are two types of B cell response to antigen. The T cell independent response does not require T cell help and the T cell dependent response does require T cell help.
===T-Cell Independent Response===
[[Image:T Cell Independent Diagram.jpg|right|thumb|150px|Diagram of the T Cell Independent Repsonse - Copyright nabrown RVC]]
*Does not require T cell help
*Activation of B cells by '''non-protinaceous antigens'''
**E.g. Activation by lipopolysaccharides only lead to [[Immunoglobulin M - WikiBlood|IgM]] production
**Act as mitogens for the B cells by stimulating cell division
*Antigens only stimulate '''primary''' immune responses (production of [[Immunoglobulin M - WikiBlood|IgM]])
*Do '''not''' stimulate memory cells
*There is no diference between the antibody response of the first exposure compared to sunsequent eposures of antigen
===T-Cell Dependent Response===
[[Image:T cell Dependent Response Diagram.jpg|thumb|right|150px|Diagram showing the T cell dependent response (primary and secondary phases) - Copyright nabrown RVC]]
*Response to '''protinaceous antigens'''
*Needs T cell help to respond appropriately
*Response occurs in germinal centres of follicles in secondary lymphoid tissues
*B cells act as antigen presenting cells on [[MHC - WikiBlood#Structure and Function Of MHC Class II|MHC II]]
*T cells interact via cell surface receptors with B cells
**CD40L on the T cell
**CD40 on the B cell
*T cells produce [[Cytokines - WikiBlood|'''cytokines''']]
**E.g. IL-4
*[[Immunoglobulins - WikiBlood#Immunoglobulin Class Switching|Class switching]] occurs from IgM
*Memory B cells are formed
====Primary T Cell Dependent Response====
* The first exposure of an individual to a particular antigen is referred to as '''priming'''
* The measurable antibody response is called the '''primary immune response'''
*Delay of 5-7 days before antibody is produced which is called the '''Lag Phase'''
*B cells undergo cloanal expansion and form plasma cells
*IgM antibody is produced first and will begin to appear in the blood. This stage is called the '''Log Phase'''
*The log phase will peak after about 10-14 days
*The '''Plateau Phase''' will then occur
*[[Immunoglobulins - WikiBlood#Immunoglobulin Class Switching|Class switching]] occurs replacing decresing levels of [[Immunoglobulin M - WikiBlood|IgM]] with [[Immunoglobulin G - WikiBlood|IgG]]
*Antibody levels will then begin to decline as plasma cells undergo apoptosis
*After primary immunisation, it usually takes around 7-10 days for a measurable antibody response to become detectable
*This latent period is the time necessary for the antigen to contact specific cells, for the cells involved to interact and expand, and for plasma cells to secrete antibody
* The first antibody to be produced in any immune response is [[Immunoglobulin M - WikiBlood|IgM]]
** This is because the gene that codes the constant domain of [[Immunoglobulin M - WikiBlood|IgM]] (Cμ) is directly downstream to the genes that code the variable antibody domain
* During primary response, [[Immunoglobulin G - WikiBlood|IgG]] production lags about a week behind that of [[Immunoglobulin M - WikiBlood|IgM]]
====Secondary T Cell Dependent Response====
*The production of antibody to any antigen ceases within a few weeks of immunisation as the antigen disappears from the body
* However, the animal retains '''immunological memory''' of the antigen
*Occurs after the primary response, i.e. the second and subsequent exposures to the specific antigen
*There is an expanded pool of memory B and T cells from the first exposure to the particular antigen
*Shorter lag phase
*Longer plateau phase as antibody persists
*There is a higher antibody titre overall due to cloanal expansion
*'''Long-lived memory cells''' which are qualitatively distinct are produced
* Retention of antigen within the immune system
** On the surface of follicular dendritic cells
** Can stimulate the immune system for years
* The level of [[Immunoglobulin M - WikiBlood|IgM]] antibody production is similar to the primary response
* The increase in antibody production occurs with [[Immunoglobulin G - WikiBlood|IgG]]
===In pathology===
===In pathology===