Changes

[[Image:B-cell immunity.jpg|thumb|right|250pxl|B-cell differentiation - B. Catchpole, RVC 2008]]

[[Image:B-cell immunity.jpg|thumb|right|250pxl|B-cell differentiation - B. Catchpole, RVC 2008]]

==Introduction==

==Introduction==

<p>Mature [[B cells]] that undergo stimulation by an antigen undergo class switching, and differentiate into either '''plasma''' or '''memory''' cells. </p>

<p>Mature [[B cells]] that undergo stimulation by an antigen undergo class switching, and differentiate into either '''plasma''' or '''memory''' cells. </p>

<p>In the paracortex region of the [[Lymph Nodes - Anatomy & Physiology|lymph node]] binding to [[Major_Histocompatability_Complexes#MHC_II|MHC II]] in the presence of Il-4 produced by the [[Lymphocytes#Helper CD4+|CD4⁺ T cells]] (Th2 type) causes the B cells to differentiate; most will become plasma cells, however small number become memory cells.</p>

<p>In the paracortex region of the [[Lymph Nodes - Anatomy & Physiology|lymph node]] binding to [[Major_Histocompatability_Complexes#MHC_II|MHC II]] in the presence of IL-4 produced by the [[Lymphocytes#Helper CD4+|CD4⁺ T cells]] (T_H2 type) causes the B cells to differentiate; most will become plasma cells, however a small number will become memory cells.</p>

Follicular dendritic cells present in the germinal centers of peripheral lymphoid organs can absorb intact antigen onto their surface to present to B cells to stimulate differentiation.

Follicular dendritic cells present in the germinal centers of peripheral lymphoid organs can absorb intact antigen onto their surface to present to B cells to stimulate differentiation.

==Plasma cells==

==Plasma cells==

===Appearance===

===Appearance===

<p>Plasma cells are oval, around 9µm and have a round prominent nucleus. The cytoplasm is extensive and strongly basophilic when stained. It contains large amounts of rough endoplasmic reticulum and the Golgi apparatus is large and appears as a clear crescent-shaped structure near the nucleus. Some plasma cells accumulate considerable quantities of, perhaps abnormal, antibody and this appears as a large eosinophilic blob filling the cytoplasm and displacing the nucleus to one side. These blobs are called "Russell Bodies".</p>

<p>Plasma cells are oval, around 9µm and have a round prominent nucleus. The cytoplasm is extensive and strongly basophilic when stained. It contains large amounts of rough endoplasmic reticulum and the Golgi apparatus is large and appears as a clear crescent-shaped structure near the nucleus. Some plasma cells, known as '''"Mott cells"''', accumulate considerable quantities of, perhaps abnormal, antibody and this appears as a large eosinophilic blob filling the cytoplasm and displacing the nucleus to one side. These blobs are called '''"Russell Bodies"'''.</p>

===Function===

===Function===

===Class switching===

===Class switching===

<p>Initially plasma cell produce [[Immunoglobulin M|Immunoglobulin M (IgM)]] however this is not always the most appropriate Ig to be produced and therefore stimulation by [[Lymphocytes#Helper CD4+|T cells]] and interleukins causes the plasma cells to undergo class switching to produce different classes of Immunoglobulins.

<p>Initially plasma cell produce [[Immunoglobulin M|Immunoglobulin M (IgM)]] however this is not always the most appropriate Ig to be produced and therefore stimulation by [[Lymphocytes#Helper CD4+|T cells]] and interleukins causes the plasma cells to undergo class switching to produce different classes of Immunoglobulins.

*In mucosal B cells plasma cells CD40 interaction (with Th2 CD40L) and Il-10 stimulates class switching to [[Immunoglobulin A|IgA]]

*In mucosal B cells plasma cells CD40 interaction (with T_H2 CD40L) and Il-10 stimulates class switching to [[Immunoglobulin A|IgA]]

*[[Eosinophils|Eosinophils]] produce Il-13 which promotes class switching to [[Immunoglobulin E|IgE]]</p>

*[[Eosinophils|Eosinophils]] produce Il-13 which promotes class switching to [[Immunoglobulin E|IgE]]</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|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|IgG]] class.</p>

====Primary T Cell Dependent Response====

====Primary T Cell Dependent Response====

* The first exposure of an individual to a particular antigen is referred to as '''priming'''

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'''. The delay of 5-7 days before antibody is produced is called the '''Lag Phase''' during which time the B cells undergo clonal 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 measurable antibody response is called the '''primary immune response'''

 

*Delay of 5-7 days before antibody is produced which is called the '''Lag Phase'''

The log phase will peak after about 10-14 days and the '''Plateau Phase''' will then occur.

*B cells undergo cloanal expansion and form plasma cells

Class switching occurs replacing decreasing levels of [[Immunoglobulin M|IgM]] with [[Immunoglobulin G|IgG]]. Antibody levels then begin to decline as plasma cells undergo apoptosis.

*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

*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 '''Plateau Phase''' will then occur

During the primary response, [[Immunoglobulin G|IgG]] production  lags about a week behind that of [[Immunoglobulin M|IgM]].

*[[Immunoglobulins#Immunoglobulin Class Switching|Class switching]] occurs replacing decresing levels of [[Immunoglobulin M|IgM]] with [[Immunoglobulin G|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

** This is because the gene that codes the constant domain of [[Immunoglobulin M|IgM]] (Cμ) is directly downstream to the genes that code the variable antibody domain

* During primary response, [[Immunoglobulin G|IgG]] production  lags about a week behind that of [[Immunoglobulin M|IgM]]

====Secondary T Cell Dependent Response====

====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

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 which occurs after the primary response - it is seen on the second and subsequent exposures to the same antigen. In effect, there is an expanded pool of memory B and T cells from the first exposure to the particular antigen which permits a shorter lag phase and a longer plateau phase as antibody persists for an extended time. There is a higher antibody titre overall due to cloanal expansion and '''Long-lived memory cells''' which are qualitatively distinct are produced.  Antigen is retained within the immune system on the surface of follicular dendritic cells and this can stimulate the immune system for years.

* 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

The level of [[Immunoglobulin M|IgM]] antibody production in the secondary response is similar to the primary response; the increase in antibody production occurs with [[Immunoglobulin G|IgG]].

*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|IgM]] antibody production is similar to the primary response

* The increase in antibody production occurs with [[Immunoglobulin G|IgG]]

===Plasma Cell Pathology===

===Plasma Cell Pathology===

==Memory cells==

==Memory cells==

<p>The differentiated cells that remain in the cortex become memory cells and these proliferate and form germinal centres in the [[Lymph Nodes - Anatomy & Physiology|lymph node]].</p>

<p>The differentiated B cells that remain in the cortex become memory cells and these proliferate and form germinal centres in the [[Lymph Nodes - Anatomy & Physiology|lymph node]].</p>

<p>Memory cells are long lived and responsible for long term immunity providing the immune system with a memory of previously encountered antigens. When they experience an antigen again they proliferate and differentiate into plasma cells. This response produces up to ten times more plasma cells than the original exposure to the antigen and is why the second immune response to an antigen is both more rapid and much stronger than the first response.</p>

<p>Memory cells are long lived and responsible for long term immunity providing the immune system with a memory of previously encountered antigens. When they experience an antigen again they proliferate and differentiate into plasma cells. This response produces up to ten times more plasma cells than the original exposure to the antigen and is why the second immune response to an antigen is both more rapid and much stronger than the first response.</p>

[[Category:Lymphocytes|C]]

[[Category:Lymphocytes|C]]

[[Category:Adaptive Immune System]]

[[Category:Adaptive Immune System]]