Le CDR3 sequence but also somatic mutations in CDR1 and CDR2 of the V gene contribute substantially to the overall BCR repertoire diversity, which was estimated to be at least 3.5 ?1010 different clonotypes [96]. More recently, the frequency of shared CDR3 sequences in memory B cells from different individuals was observed to occur at a frequency of approximately one in 4000 clonotypes [74]. Most of these recurrent instances of clones were likely the result of rare recurrent recombinationand not selection as they were mostly un-switched, un-mutated and had short CDR3s [74]. These estimates appear to indicate that occurrences of independently generated overlapping CDR3 sequences are quite rare, although if we consider multiple samples from multiple experiments, the number will increase. However, it is important to note two caveats to this low estimate: (i) these calculations assume full knowledge of the source of the CDR3 positions. In reality, owing to sequencing errors and the difficulty in identifying D gene associations [49], we must be satisfied with identifying all sequences that have a CDR3 that is `close Isorhamnetin biological activity enough’. (ii) To make our calculation, we assume that all combinations are equally likely to occur (that they are uniformly distributed), but this is not true. For example, some VH genes (such as the 30 VHs in fetal life, [97]) rearrange more frequently than others. Moreover, repertoires from mature or memory B cells have undergone additional rounds of selection; IgH rearrangements that are positively selected will be more numerous owing to clonal expansion. The erroneous classification of two independent clones as a single clone can also occur. The generation of clonally distinct yet highly similar antibodies may be more likely under certain circumstances. B1 B cells tend to harbour shorter CDR3 sequences, exhibit skewed VH gene usage and at least a subset of B1 cells can have low levels of SHM [98,99]. All of these properties make it easier for B1 B cells to harbour highly similar antibodies than B2 B cells. A second circumstance could arise if different L chains rearrange in different clones that actually share the same antibody H chain. This hypothetical scenario is possible because pre-B1 cells undergo multiple rounds of cell division prior to the initiation of L chain rearrangement [5]. In a clone with a favourable H chain, there could be as many as seven rounds of rearrangement, generating up to 128 pre-B cells with the same H chain. If L chain rearrangements in B cells with the same H chain gene rearrangement occur independently, then the same H chain could be found in combination with many different L chains. Consistent with this idea, studies with the E12 cell line, which can differentiate from the pro-B stage all the way to B cells in culture, demonstrate that subclones with the same VH rearrangement can have different L chain rearrangements [100]. An interesting prediction of this theory is that, independent of the H chain specificity, the number of rounds of pre-B cell division could dictate how many different L chain partners a given H chain can have. A third setting in which similar or identical H chains could be independently created occurs when there is positive selection for independent B cell clones with shared amino acid sequence motifs that bind to one or more Miransertib web particular antigens. Such sharing has been given a variety of names including `public CDR3s’ and `stereotyped receptors’ and has been documented in man.Le CDR3 sequence but also somatic mutations in CDR1 and CDR2 of the V gene contribute substantially to the overall BCR repertoire diversity, which was estimated to be at least 3.5 ?1010 different clonotypes [96]. More recently, the frequency of shared CDR3 sequences in memory B cells from different individuals was observed to occur at a frequency of approximately one in 4000 clonotypes [74]. Most of these recurrent instances of clones were likely the result of rare recurrent recombinationand not selection as they were mostly un-switched, un-mutated and had short CDR3s [74]. These estimates appear to indicate that occurrences of independently generated overlapping CDR3 sequences are quite rare, although if we consider multiple samples from multiple experiments, the number will increase. However, it is important to note two caveats to this low estimate: (i) these calculations assume full knowledge of the source of the CDR3 positions. In reality, owing to sequencing errors and the difficulty in identifying D gene associations [49], we must be satisfied with identifying all sequences that have a CDR3 that is `close enough’. (ii) To make our calculation, we assume that all combinations are equally likely to occur (that they are uniformly distributed), but this is not true. For example, some VH genes (such as the 30 VHs in fetal life, [97]) rearrange more frequently than others. Moreover, repertoires from mature or memory B cells have undergone additional rounds of selection; IgH rearrangements that are positively selected will be more numerous owing to clonal expansion. The erroneous classification of two independent clones as a single clone can also occur. The generation of clonally distinct yet highly similar antibodies may be more likely under certain circumstances. B1 B cells tend to harbour shorter CDR3 sequences, exhibit skewed VH gene usage and at least a subset of B1 cells can have low levels of SHM [98,99]. All of these properties make it easier for B1 B cells to harbour highly similar antibodies than B2 B cells. A second circumstance could arise if different L chains rearrange in different clones that actually share the same antibody H chain. This hypothetical scenario is possible because pre-B1 cells undergo multiple rounds of cell division prior to the initiation of L chain rearrangement [5]. In a clone with a favourable H chain, there could be as many as seven rounds of rearrangement, generating up to 128 pre-B cells with the same H chain. If L chain rearrangements in B cells with the same H chain gene rearrangement occur independently, then the same H chain could be found in combination with many different L chains. Consistent with this idea, studies with the E12 cell line, which can differentiate from the pro-B stage all the way to B cells in culture, demonstrate that subclones with the same VH rearrangement can have different L chain rearrangements [100]. An interesting prediction of this theory is that, independent of the H chain specificity, the number of rounds of pre-B cell division could dictate how many different L chain partners a given H chain can have. A third setting in which similar or identical H chains could be independently created occurs when there is positive selection for independent B cell clones with shared amino acid sequence motifs that bind to one or more particular antigens. Such sharing has been given a variety of names including `public CDR3s’ and `stereotyped receptors’ and has been documented in man.
http://calcium-channel.com
Calcium Channel
