Frequency of Immunoglobulin E Class Switching Is Autonomously Determined and Independent of Prior Switching to Other Classes (1)
IgE switches recombina- tions, and the fact that in vitro, the appearance of IgE+ cells in LPS/IL-4 culturescanbe largely suppressed by anti-IgG1 antibodies.
Spleen cells were cultured in 3 ml medium at a concentration of 5 x 10^5/ml in 6-well plates, and in 50 ml at 10^6/ml in 250-ml bottles with RPMI 1640 containing 40 ug/ml bacterial LPS.
The titers of total serum IgE of homozygous neo^5’Sg1 mice on day 13 after infection were similar to those in wild-type mice, whereas their titers of serum IgG1 were at least 60-fold reduced. Titers of NP-specific IgE reached identical levels. Thus, expression of IgE in vivo is not impaired in mice that cannot perform class switching to IgG1.
Virtually no IgGl-expressing (<0.1%), but 4.6% (+ 1.1%) IgE-expressing homozygous ^5’Sg1 cells were induced. The frequency of IgE + cells was even higher than in cultures of wild-type cells (2.0 -+ 0.5%), suggesting that sequential switching to IgE via IgG1. After 5 d of culture with LPS and IL-4, cells from ^5’Sg1 and control mice, stained for IgM and IgE in the cytoplasm, were isolated by fluorescence-activated cell sorting to a purity of 98% for IgM + cells and 95 and 99% for IgE + ^5’Sg1 and control cells, respectively.
The extent of rearrangement and deletion could be inferred from the relative numbers of switch (SH) and constant region gene segments (CH), respectively, retained in germline configuration.
The lack of switch recombination on inactive IgH alleles of IgE + cells shows that class switching to IgE is independent of prior switch recombination to any other class.