B-cell development
鄰家的妹妹，天真少女（IgM,IgD）
男人薰陶，則成----？
阿姨或雞。（IgA,,IgE, IgG）
故初戀不可不慎也。
且看：
B-cell maturation consists of early(antigen-independent) and late (antigen-dependent) stages. 鄰家的妹妹，天真少女（IgM,IgD）
Early development is initiated by therearrangement of genes for the heavy and light chains of antibodies, a processreferred to as V/(D)/J recombination.
The earliest B-precursor cell showsrearrangement of the immunoglobulin heavy chain, which is then followed bylight chain rearrangement.
The kappa light chain genes rearrange first, if neither kappa locus is productively rearranged, then the lambda geneloci undergo rearrangement.
Once a successful light chainrearrangement occurs, the cell will express the complete immunoglobulinmolecule on its surface, which identifies it as a mature B cell.
Mature B cells will typically expresseither immunoglobulin M (IgM) or immunoglobulin D (IgD) on their surface, 鄰家的IgD妹妹IgM，天真少女（IgM,IgD）andthis surface expression is critical to cell survival. Further, the combinationof the VDJ gene sequences is unique for each immunoglobulin molecule variableregion and, hence, each B cell and is referred to as the idiotype.
CD 10, CD 19, TdT. and CD20.
Cell surface markers are also used to define the early stages of B-celldevelopment.
CD10 (CALLA, the common acute lymphoblastic leukemia antigen) and CD19 areexpressed on immature B cells (pro-B and B precursor) that have begun heavychain rearrangement.
Terminal deoxynucleotidyl transferase(TdT), a DNA polymerase important for nucleotide chain elongation during generearrangement, is also expressed at this stage.
CD20 is then expressed as cells rearrangelight chains and express surface immunoglobulin, and the expression of CD10 andTdT is lost. 少女初長成也
The mature but antigen-naive B cell leavesthe bone marrow to circulate and populate lymphoid organs such as lymph nodes,spleen, and mucosa-associated lymphoid tissue (MALT).走出家門，初入社會。
The late, or antigen-dependent, stages ofB-lymphocyte development begin when a naive B cell recognizes an antigen( 男人) with its membrane-bound antibody.
(少女遇某男也）
These B cells collect in germinal centersof the various lymphoid organs and begin to divide and undergo several types ofgenetic modification.
Somatic hypermutation is a process bywhich cells introduce mutations into the variable region (V) genes. Thesemutations result in antibodies that may have a higher or lower affinity for theantigen. Those that produce a higher affinity antibody (一見鍾情，情竇初開) will persist and become either plasma cells ormemory B cells, whereas those that fail to produce functional antibody at thisstage will undergo apoptosis.(抑鬱寡歡而終如林妹妹)
Class switching involves changing the heavy chain that is expressed toproduce other antibody classes: immunoglobulin G (IgG), immunoglobulin A (IgA),or immunoglobulin E (IgE). 阿姨或雞.
Although this switch does not alterantibody affinity, the change in class of antibody will alter its effectorfunction and thereby affect the immune response.
故曰：
鄰家妹妹，天真少女，（IgM,IgD）, CD10, CD 19, TdT. and CD20.
男人薰陶，阿姨或雞。（IgA,,IgE, IgG）
故初戀不可不慎也。
古人云：男人怕入錯行，女人怕嫁錯郎，誠如是也。