Positive selection of low affinity autoreactive B cells

Types of tolerance seen in autoreactive phosphocholine-specific B cells are dependent on the idiotype of the receptors expressed

Phosphocholine (PC) is the immunodominant epitope found on the surface of a number of microorganisms, including Streptococcus pneumoniae (SPn), and is thought to play a vital role in the pathogenesis of SPn. B cells expressing M167Hκ24L immunoglobulin receptors specific for PC have been shown to be autoreactive in that they undergo clonal deletion in both X-linked immune-deficient and Rag(-/-) mice. We have now shown that B cells expressing M603Hκ8L PC-specific receptors also delete in Rag(-/-) mice, whereas those expressing T15Hκ22L transgenes do not delete. However, T15Hκ22L B cells are lost in normal heterozygous transgenic mice because they cannot compete with normal B cells. These data indicate that M167Hκ24L and M603Hκ8L PC-specific B cells are recognizing an autoantigen expressed on membranes which causes them to downregulate their receptors and clonally delete, while T15Hκ22L B cells are tolerized by a soluble form of PC-antigen which results in their being trapped in the spleen. Thus, the types of tolerance seen in autoreactive PC-specific B cells are dependent on the idiotype of the receptors expressed.

Global analysis of B cell selection using an immunoglobulin light chain-mediated model of autoreactivity

The nature of the immunoglobulin light chain affects peripheral B cell tolerance and autoreactivity.

The important subtleties of B cell tolerance are best understood in a diverse immunoglobulin (Ig) repertoire context encoding a full spectrum of autoreactivity. To achieve this, we used mice expressing Igκ transgenes that confer varying degrees of autoreactivity within a diverse heavy chain (HC) repertoire. These transgenes, coupled with a biomarker to identify receptor-edited cells and combined with expression cloning of B cell receptors, allowed us to analyze tolerance throughout B cell development. We found that both the nature of the autoantigen and the Ig HC versus light chain (LC) contribution to autoreactivity dictate the developmental stage and mechanism of tolerance. Furthermore, although selection begins in the bone marrow, over one third of primary tolerance occurs in the periphery at the late transitional developmental stage. Notably, we demonstrate that the LC has profound effects on tolerance and can lead to exacerbated autoantibody production.